Hello.

Looks nice. Out of curiosity what are the dimensions of your room?
Regards,
John(W)25' X (L)27' ceiling is about 7'2".

The foam behinfd the TV is to kill any hum/buzzing from amps/TV and it works quite well if there are any noises...also looks awesome when watching a movie. I can't get a 242 back there or I would.

I am working with a small 13' long by 14' wide room with 6'9" walls that slope up to a 9' ceiling. The front wall (where the projector screen and towers will be) has inverted corners. So instead of the walls meeting at a point facing away from the center of the room, there is a painted drywall "column" in the corner with a point facing the center of the room.

The room is carpeted and all walls are textured and painted drywall with no existing acoustical treatments. The back of the room is mostly open but will eventually be covered with thick velvet-like drapery.

How will these inverted corners affect the room acoustics? Am I more or less in need of acoustical treatment for these corners?

If you've not yet read the fine, comprehensive Ethan Winer tutorial on many of these issues, you may find it of interst. It's here (http://www.ethanwiner.com/acoustics.html), and quite good.

Very informing, indeed.

That basically answered my questions. As with many here--I have "constraints" that I must work within as this is not a dedicated theater room. I can see myself buying some OC705 this week, and getting busy with at least some corner traps, and surrounding my mains and surrounds (tower speakers in corners) with panels on both corner sides. NOT ideal--but most definately an improvement I hope.

...Doesn't help that my living room has:
1. wood floors (larger area rug)
2. 18 foot ceilings
3. Opens into kitchen and front foyer.
4. Acoustic nightmare!!!:eek:

I can see myself buying some OC705 this week, and getting busy with at least some corner traps,

what thickness (or size of facing if doing corner super chunks) are you going with? if of sufficient size, you'll want to use a material with lower flow-resistivity like pink, fluffy attic insulation (uncompressed/loosely filled).

Has anyone heard of this stuff?

http://www.armacell.com/www/armacell/armacell.nsf/ansHTMLSeitenLookUp/INT-Sound_Frame?OpenDocument

The fella at SPI told me about it. It's a little more expensive than 703, but no fiberglass.

How does this stuff's abilities compare to OC and/or mineral wool?

...Not sure how to interpret the provided table:confused:

Has anyone heard of this stuff?

http://www.armacell.com/www/armacell/armacell.nsf/ansHTMLSeitenLookUp/INT-Sound_Frame?OpenDocument

The fella at SPI told me about it. It's a little more expensive than 703, but no fiberglass.

How does this stuff's abilities compare to OC and/or mineral wool?

...Not sure how to interpret the provided table:confused:

I use it almost daily in the A/C industry for thermal pipe wrap or insulation. What I can tell you is this product will come in a roll. It will probably not work all that great for our wall treatments. If you were to stand it on end... It will flop over, cause its not rigid. If you were to make a frame for it, I'd say you would need to install 1/8" door skin or "luan" to the back of the frame. Then glue the armacell to the backing within the frame. If you were to simply set it inside a frame and stand on end.... It would "in time" compress and start to buckle. The other option would be to glue it directly to your wall like you would with the other "foam" style products.

I personally haven't seen anybody mention the use of this product for acoustic panels yet. Probably would be better to stuck with rigid 703 and or 705 panels as that seems to be what most people are using. The roxul brand is mineral wool not fiberglass as previously stated a few pages back, but that is also not as rigid as 703-705 and may need additional support as well. There are some other (green) products out there but they are still a bit more pricey and less rigid as well. Food for thought :)

For some reason, the URL I pasted goes to the wrong part of the website. There is a selection on that link under products for the "sheet and roll" type product. You are certainly correct, as it can be bought in rolls, but it also shows a panel type piece.

I may head back to SPI today to see if they have some i can compare to the 703 and/or mineral wool.

Once again--Is 705 better than 703 at the same thickness because it is denser???

Once again--Is 705 better than 703 at the same thickness because it is denser???

better at *what*?

density isn't the key value regarding a porous insulation's absorption characteristics, but gas-flow-resistivity (along with thickness, angle of incidence). density and flow-resistivity are generally linear, but two materials with identical densities can have differing flow-resistivity values.

if you read Ethan's paper of which FOH linked to above, you'll know porous insulation is a velocity-based absorber (converts kinetic energy into heat via friction of the waveform passing through the porous material). hence, to be effective, the insulation must be placed in areas of high particle velocity. velocity is zero directly at the boundary (and pressure is max; as pressure and velocity are inversely proportional), hence we generally need thick absorption (or utilize an air-gap to space the insulation away from the boundary) such that the insulation is in areas of high particle velocity for the relevant frequencies.

the problem with higher GFR (denser) materials, is they will begin to reflect at higher frequencies (and grazing angles).

for broadband panels for reflections:
normally, one would measure (via the ETC) to identify whether any high-gain early specular reflections are impeding the listening position. some speakers do not throw off-axis energy to the sidewalls, thus there may be no reason to apply broadband absorption in the first place. however, for most speakers, that is not the case.

4" thickness OC703 (3pcf) or Mineral Wool (4pcf) with 2-4" air-gap should be sufficient for the broadband panels to attenuate specular reflections. the lower specular region will extend down to 250-300hz (depending on room dimensions), and typical speakers will increase the amount of off-axis energy dispersed to the side-walls as frequency lowers --- thus, your panels need to be sufficiently thick and effective to attenuate the lower specular region (which also contains inherently more energy content). many use thin absorption which merely attenuates the mid-HF band and allows the lower specular region to persist - coloring, filtering, "EQ'ing" the reflection. i would stay away from OC705 for sidewall panels - they are more expensive than OC703 and can possibly reflect higher freq content.

most batts/panels come in 2" thickness - so you can stack 2 panels together to form a 4" absorber. you can use a dab of 3M spray glue in the corners to bond the two 2" panels together, but DO NOT apply the spray glue to the whole face of the panel - as the glue will block the porous holes and create unexpected results (can become reflective). use just a quick dab in each corner. building a frame out of 1.5"-2" wood will allow you to create an air-gap (spacing the insulation from the boundary, increasing it's effectiveness) as well as make it easy to hang the panel like a picture frame.

also note that as angle of incidence increases (away from 0* normal incidence (perpendicular to the panel), the wave essentially "sees" a thicker panel because when ingress from an angle, it is traveling through more insulation - so the absorption coefficient goes up. HOWEVER, as you approach grazing angles, the panel will begin to REFLECT, just like a stone skipping off water.

in this example, a 4" thick panel is placed flat on the wall/boundary. notice how the blue wave entering at normal incidence (0*, perpendicular from the panel) "sees" a 4" thick porous absorber. the red wave traveling at, say ~50*, comes in diagally at essentially "sees" a thicker panel! however, at high grazing angles (approaching 90* which is parallel to the panel/boundary), the energy grazes off the panel. (very simplified diagram, ignoring many other factors):

http://img829.imageshack.us/img829/9605/testmsg.png

here are some examples of how absorption coefficient INCREASES as angle of incidence moves away from normal (thus, the wave "sees" a thicker absorber), and then DECREASES as angle of incidence approaches grazing angle.

http://img408.imageshack.us/img408/3219/50017455.gif

http://img402.imageshack.us/img402/5795/38868855.gif

http://img855.imageshack.us/img855/5592/49526441.gif

http://img221.imageshack.us/img221/9955/42422579v.gif

http://img100.imageshack.us/img100/2383/19592584.gif

http://img696.imageshack.us/img696/4430/64908024.gif

http://img812.imageshack.us/img812/8114/86803612.gif


now, for the modal region (bass/LF), the energy has wave properties and can no longer be modeled like specular energy (geometry). the waves are huge thus we place the absorber in the corner where the boundaries force the energy through the insulation (vs the large wavelengths simply diffracting around the panels). 3D corners will attack all 3 axial modes in the room, and 2D corners will attack the 2 axial modes relevant to those 2 boundaries.

for the corner porous bass traps (LF absorbers), if you are using a relatively thin panel then the denser is better. but since porous insulation is a velocity-based absorber, there is really no point in using thin absorption here (regardless of density/GFR). the LF modal wavelengths are large and contain the most energy content - thus the LF porous corner absorbers need to be as thick as possible. when building thicker and thicker corner traps, you need to use a material with lower gas-flow-resistivity. pink fluffy attic insulation (loosely filled/uncompressed) will perform best for LF absorber if you can build 34" faced traps or thicker. it will be a cheaper and more effective solution.

pink fluffy is 5000rayls/s gas-flow-resistivity
OC703 is 16,700rayls/s (but NASA tested somewhere around 37,000 IIRC (document is at home). OC705 is even higher GFR.

200mm
http://img265.imageshack.us/img265/4896/200mmpaneldifferentflow.gif

300mm w/ 300mm air-gap:
http://i.imgur.com/buwNv.gif

a very common misconception is that denser is better! as you make the corner trap thicker and thicker (with denser material), the energy can no longer penetrate through all of the small, porous holes, and essentially the corner "absorber" begins to reflect! it is still not very well accepted that thick traps made from low GFR material perform better, but what can you do...

another issue is, you really cannot have too much LF porous absorption within a room ... but the LF porous absorber will also inadvertantly absorb specular energy within the room as well! with lots of surface area and thick corner traps (required for effective LF absorption), you will create a very dead/damped room. thus, we generally apply a reflective membrane to the corner bass traps such that some mid-HF specular energy is reflective to preserve energy within the room. you can use 6mil plastic to wrap your corner bass traps in ... as bass traps do not need acoustically transparent fabric like the broadband panels do.

^^^

Killer post local:)

Good lookin' out wrt grazing angles/angle of incidence in general.

What's the definition of 2% perforated panel? Also, the final graphic "300mm w/ 300mm air-gap", seems a combo of the two would offer the ideal characteristics. Not acoustically in series, but perhaps half and half,...ever seen such a thing around GS or elsewhere?

Also, ever seen these (http://webapps.easy2.com/cm2/flash/generic_index.asp?page_id=36044183) plastic wrapped batts? Not sure how the plastic thickness affects things, however at least they'd be a pleasure to handle. They seem ideal:cool:

:eek:

That post was amazing and interesting as can be. Thank's for that. I believe that I have made a decision regarding what combinations I will be using.

I will likely go with 3" mineral wool behind the front and rear speakers which are in corners. (I will basically "line" the corners with the 2X4' panels,as my tower speakers are 39" tall).

Then, I will likely use OC703 panels covered in fabric in a few places on the walls themselves.

I have to believe ( and REALLY hope) that I will hear an improvement, as my living room has ZERO treatment thus far, and with 18' celings/wallls and wood floors--I've got an acoustic mess!

Very informative post Local...nice job.

better at *what*?

density isn't the key value regarding a porous insulation's absorption characteristics, but gas-flow-resistivity (along with thickness, angle of incidence). density and flow-resistivity are generally linear, but two materials with identical densities can have differing flow-resistivity values.

if you read Ethan's paper of which FOH linked to above, you'll know porous insulation is a velocity-based absorber (converts kinetic energy into heat via friction of the waveform passing through the porous material). hence, to be effective, the insulation must be placed in areas of high particle velocity. velocity is zero directly at the boundary (and pressure is max; as pressure and velocity are inversely proportional), hence we generally need thick absorption (or utilize an air-gap to space the insulation away from the boundary) such that the insulation is in areas of high particle velocity for the relevant frequencies.

the problem with higher GFR (denser) materials, is they will begin to reflect at higher frequencies (and grazing angles).

for broadband panels for reflections:
normally, one would measure (via the ETC) to identify whether any high-gain early specular reflections are impeding the listening position. some speakers do not throw off-axis energy to the sidewalls, thus there may be no reason to apply broadband absorption in the first place. however, for most speakers, that is not the case.

4" thickness OC703 (3pcf) or Mineral Wool (4pcf) with 2-4" air-gap should be sufficient for the broadband panels to attenuate specular reflections. the lower specular region will extend down to 250-300hz (depending on room dimensions), and typical speakers will increase the amount of off-axis energy dispersed to the side-walls as frequency lowers --- thus, your panels need to be sufficiently thick and effective to attenuate the lower specular region (which also contains inherently more energy content). many use thin absorption which merely attenuates the mid-HF band and allows the lower specular region to persist - coloring, filtering, "EQ'ing" the reflection. i would stay away from OC705 for sidewall panels - they are more expensive than OC703 and can possibly reflect higher freq content.

most batts/panels come in 2" thickness - so you can stack 2 panels together to form a 4" absorber. you can use a dab of 3M spray glue in the corners to bond the two 2" panels together, but DO NOT apply the spray glue to the whole face of the panel - as the glue will block the porous holes and create unexpected results (can become reflective). use just a quick dab in each corner. building a frame out of 1.5"-2" wood will allow you to create an air-gap (spacing the insulation from the boundary, increasing it's effectiveness) as well as make it easy to hang the panel like a picture frame.

also note that as angle of incidence increases (away from 0* normal incidence (perpendicular to the panel), the wave essentially "sees" a thicker panel because when ingress from an angle, it is traveling through more insulation - so the absorption coefficient goes up. HOWEVER, as you approach grazing angles, the panel will begin to REFLECT, just like a stone skipping off water.

in this example, a 4" thick panel is placed flat on the wall/boundary. notice how the blue wave entering at normal incidence (0*, perpendicular from the panel) "sees" a 4" thick porous absorber. the red wave traveling at, say ~50*, comes in diagally at essentially "sees" a thicker panel! however, at high grazing angles (approaching 90* which is parallel to the panel/boundary), the energy grazes off the panel. (very simplified diagram, ignoring many other factors):

here are some examples of how absorption coefficient INCREASES as angle of incidence moves away from normal (thus, the wave "sees" a thicker absorber), and then DECREASES as angle of incidence approaches grazing angle.

now, for the modal region (bass/LF), the energy has wave properties and can no longer be modeled like specular energy (geometry). the waves are huge thus we place the absorber in the corner where the boundaries force the energy through the insulation (vs the large wavelengths simply diffracting around the panels). 3D corners will attack all 3 axial modes in the room, and 2D corners will attack the 2 axial modes relevant to those 2 boundaries.

for the corner porous bass traps (LF absorbers), if you are using a relatively thin panel then the denser is better. but since porous insulation is a velocity-based absorber, there is really no point in using thin absorption here (regardless of density/GFR). the LF modal wavelengths are large and contain the most energy content - thus the LF porous corner absorbers need to be as thick as possible. when building thicker and thicker corner traps, you need to use a material with lower gas-flow-resistivity. pink fluffy attic insulation (loosely filled/uncompressed) will perform best for LF absorber if you can build 34" faced traps or thicker. it will be a cheaper and more effective solution.

pink fluffy is 5000rayls/s gas-flow-resistivity
OC703 is 16,700rayls/s (but NASA tested somewhere around 37,000 IIRC (document is at home). OC705 is even higher GFR.

200mm

300mm w/ 300mm air-gap:

a very common misconception is that denser is better! as you make the corner trap thicker and thicker (with denser material), the energy can no longer penetrate through all of the small, porous holes, and essentially the corner "absorber" begins to reflect! it is still not very well accepted that thick traps made from low GFR material perform better, but what can you do...

another issue is, you really cannot have too much LF porous absorption within a room ... but the LF porous absorber will also inadvertantly absorb specular energy within the room as well! with lots of surface area and thick corner traps (required for effective LF absorption), you will create a very dead/damped room. thus, we generally apply a reflective membrane to the corner bass traps such that some mid-HF specular energy is reflective to preserve energy within the room. you can use 6mil plastic to wrap your corner bass traps in ... as bass traps do not need acoustically transparent fabric like the broadband panels do.

LH,

Why is pink fluffy a better solution for corner traps if it has 3x lower gfr than OC703? It should be calculable to determine at what density and thickness of different materials certain frequencies begin to be reflected. Why not a table then? I can see where this is possible but at what thickness does this affect the frequencies we're targeting for corner traps?

Why is it not commonly accepted that pink fluffy is better? I have seen you are quite the activist for this position, do experts in acoustics generally agree or disagree with this statement?

Why is it not commonly accepted that pink fluffy is better? I have seen you are quite the activist for this position, do experts in acoustics generally agree or disagree with this statement?

I posed a similar question a few months ago in this massive thread, and it started a pi$$ing match between some folks. I wasn't convinced that the pink fluffy was any better, but I would really like for some simple, no-nonsense proof that it is since it is definitely a lot cheaper. Unfortunately, it would probably take one of us "average" users to measure a room, then put up a pink fluffy trap and measure, and lastly, take down the pink fluffy trap and make a super chunk or straddling trap out of the OC703 or 705 stuff and measure again. Post the results, and see what happens.

My theater is still in the construction phase and will be for a while since I am finishing my entire basement at the same time, plus I will have so much other stuff to fix, that I won't have the time to dedicate to the testing, building, testing, building, and testing. If I had to do all of that, I would skip the pink fluffy and just go with the 703/705 stuff since I would need to buy/build it anyway for the test.

LH127:

Now that lengthy post is impressive!!! ;) 2 thumbs up and a handshake. Thanks for the great info.... Now I need to cut and paste to my desk top for quick reference.

LH,

Why is pink fluffy a better solution for corner traps if it has 3x lower gfr than OC703?

porous insulation is a velocity-based absorber - and must be placed throughout areas of high particle velocity in order to be effective. the modal-region wavelengths are very long, which requires thick porous absorbers. as you make thicker and thicker traps, you are making it more difficult for sound to penetrate through the series of interconnected pores of the material. with too high a GFR, the impedance mismatch between the air and the absorbent will causes the sound to reflect from the outer-face.

think of it this way - the acoustically transparent (porous) fabric you use for your broadband panels...has low flow resistivity and allows sound to pass through it freely (close surface impedance to air). you can freely blow through it (and that is the test we tell people to use when procuring). now, double up the layer and try blowing through it again. continue adding layers (increasing thickness), and eventually air will not be able to freely pass through the porous holes of the fabric and it will instead reflect off (very high GFR).

thus, as the thickness of the absorber is increased, it will become more effective to use a material with lower gas-flow-resistivity such that the sound can still penetrate through the material.

http://img851.imageshack.us/img851/2448/aborptioncharacteristic.png

http://img14.imageshack.us/img14/9132/flowresistivitydefiniti.png

via: http://www.amazon.com/Acoustic-Absorbers-Diffusers-Theory-Application/dp/0415471745

It should be calculable to determine at what density and thickness of different materials certain frequencies begin to be reflected. Why not a table then? I can see where this is possible but at what thickness does this affect the frequencies we're targeting for corner traps?

http://www.whealy.com/acoustics/Porous.html

note: "The transfer matrix calculations in this spreadsheet are reimplementations of the MATLAB scripts printed in Appendix B of the first edition of Trevor Cox and Peter D'Antonio's book Acoustic Absorbers and Diffusors. Theory, Design and Application ."

AMFG SoundFlow:
http://soundflow.afmg.eu/index.php/sf-features-en.html

(and this is without going into details of particular methods of obtaining absorption coefficients, and which are necessarily relevant - for simplicity).


Why is it not commonly accepted that pink fluffy is better? I have seen you are quite the activist for this position, do experts in acoustics generally agree or disagree with this statement?

anywhere professional is likely going to be using a combination, but primarily resonator/tuned traps (pressure-based absorbers, thus not limited to the thickness requirements of porous, velocity-based absorbers). thick, broadband porous traps are more likely found in diy environments (relatively cheap to construct, materials easy to procure, little design work, works without trial-and-error as with tuned traps).

the diy community is generally constricted to very small rooms, which is not ideal due to having little real estate for such thick, porous LF absorbers. the issues are compounded because the modal issues become more detrimental as the room becomes smaller, yet simultaneously, as the room becomes smaller you have less room for effective porous LF absorption. resonator (pressure-based traps) are more difficult to construct, but are more efficient when placed in areas of high particle pressure (which, conveniently, is against the boundary).

and actually, it is commonly accepted re: pink fluffy (low GFR), just not in such areas as this and many other forums within the DIY audio crowd. the "oc703 superchunks ©" have been shown to be effective, thus they are copied and utilized within the diy community without little questioning as to the details. the strange thing is that people automatically misassume that denser is better, and always seem to ask questions regarding "the next denser product", and whether that will perform any better? but it's funny to think about how many dont even consider to ask questions in the other direction regarding less dense (lower GFR) material. it's always towards the denser spectrum that questions are presented.

there seems to be little discussion of porous material characteristics and details for optimal LF absorption except in a few areas. such continued assumptions and general lack of understanding of the components are probably why there is a general stigma regarding porous absorption that many seem to chime in with, regarding that "it is useless because it cannot absorb below 125, 100hz, etc".


edit:

Why is it not commonly accepted that pink fluffy is better?

because of responses like this that ignore any of the data and continue to believe that their intuition regarding acoustics is never wrong?

If I had to do all of that, I would skip the pink fluffy and just go with the 703/705 stuff since I would need to buy/build it anyway for the test.

the bulk of my intuitions have been proven wrong over and over - welcome to acoustics

here is the NASA document - they put oc703 at 27,000 (not 16,000rayls as commonly asserted):
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19880003624_1988003624.pdf

http://img545.imageshack.us/img545/8621/nasaoc3350vs703.jpg

the lighter (3350 @ 4100rayl/s) vs OC703

So given the above (And thank you localhost127!) it seems that it should be relatively easy to determine the maximum effective size of a corner bass trap made out of OC703 vs. "Pink Fluffy", since we know the shape (triangular) and the GFR values for this material.

That might make it easier to recommend one material over the other when people have questions about building these types of bass traps. (For example: Under 12" face = no impact, 12" to 24" face = OC703, Over 24" = Pink Fluffy)

I don't understand the formulas myself, or I'd make the attempt.

hannes offers some nice commentary and diagrams:
http://www.gearslutz.com/board/6328646-post88.html

http://www.gearslutz.com/board/6281432-post46.html

http://www.gearslutz.com/board/1913176-post29.html
http://www.frischat.com/compose/Reflection_and_trans02.jpg

and as he noted, if denser is better, then why does oc701 outperform oc703, oc705 in this example - and notice how the lightest material performs best at 125hz (relative to other materials).
http://img513.imageshack.us/img513/8610/bobgold.jpg


As Andre states, you are dealing with the acoustical Impedance of the boundary material.

Please note this and be careful as so many are want to reduce absorption to resistance - which is only one part of the complex impedance.

And this issue becomes very important if one stops for a moment and examines that the the reactance has both capacitive and inductive components which function not only as frequency selective resistance with a time aspect, but which also impact the energy aspects of the system behavior, as the real domain which corresponds to resistance also correlates to the potential energy in the system, while the imaginary realm corresponds to the reactance component and the kinetic energy of the system, which relate directly with pressure and velocity aspects (and more) of the overall system.

One makes a significant mistake to reduce the absorption model to simply a function of 'resistance'.


more if interested:

http://www.gearslutz.com/board/studio-building-acoustics/514620-q-4-avare.html

http://downloads.bbc.co.uk/rd/pubs/reports/1992-11.pdf
(note fig9 pg4 - covering porous bass traps with reflective plastic membrane to reflect mid-hf specular content back into the room):
http://img220.imageshack.us/img220/4433/bbcplasticcoveringforpo.png


http://www.rockwool.it/files/RW-IT/file/Gamma%20Prodotti/Prodotti%20marina/Acoustic_Manual_vers3_web.pdf (section 2)

http://www.rockwool.it/download/software

oh, and on the subject of this (flow-resistivity along with oc703/superchunks), it may be wise to note that the flow-resistivity of oc703 when mounted as a panel on a boundary will be different than a oc703 superchunk --- in the superchunk, the "edge" of the individual oc703 panel (before cutting) is functioning as the outer-face of the absorber.

What's the definition of 2% perforated panel? Also, the final graphic "300mm w/ 300mm air-gap", seems a combo of the two would offer the ideal characteristics. Not acoustically in series, but perhaps half and half,...ever seen such a thing around GS or elsewhere?

in that model, ...only if you had a very specific issue at ~24hz ... and if so, you wouldn't be able to implement both within the same corner. efforts would be better spent with resonator trap for the specific, low octave issue (and porous absorption for broadband). any mixing of the two in the same corner would yield impedance issues (could likely be modeled via SoundFlow) - but not entirely predictable (eg, depends on how wave is incident to corner).

Also, ever seen these (http://webapps.easy2.com/cm2/flash/generic_index.asp?page_id=36044183) plastic wrapped batts? Not sure how the plastic thickness affects things, however at least they'd be a pleasure to handle. They seem ideal:cool:

you would have many instances of impedance changes throughout the trap.

Acoustic Performance

Acoustic Performance

Random incidence
absorption coefficient
acc. to EN ISO 354 125 250 500 1 000 2 000 4 000

at 10 mm 0.02 0.04 0.08 0.19 0.53 0.44

at 32 mm 0.08 0.17 0.51 0.56 0.25 0.24
This is the absorbtion table (i think) from the armaflex website that my local SPI insulation warehouse manager recommended. It's supposedly nice and rigid, requiring no frame, and is fairly cost competitive with other options. Can anyone evaluate this table an comment on the effectiveness of this product???

Sorry that the table is out of alignment, at 125, the 0.02 and 0.08 should be directly underneath

Acoustic Performance

Acoustic Performance

Random incidence
absorption coefficient
acc. to EN ISO 354 125 250 500 1 000 2 000 4 000

at 10 mm 0.02 0.04 0.08 0.19 0.53 0.44

at 32 mm 0.08 0.17 0.51 0.56 0.25 0.24
This is the absorbtion table (i think) from the armaflex website that my local SPI insulation warehouse manager recommended. It's supposedly nice and rigid, requiring no frame, and is fairly cost competitive with other options. Can anyone evaluate this table an comment on the effectiveness of this product???

Sorry that the table is out of alignment, at 125, the 0.02 and 0.08 should be directly underneath

You are going to want to make those no less then 100mm thick and straddle corners if you want to use them as broad band bass traps. Honestly I would recommend thicker then that if you can. ;)

Figured I would update with some pics, I have 4 QRD's to be ordered and placed or rear side walls to complete the room.

http://img39.imageshack.us/img39/3228/img0989ss.jpg


Right MLP:

http://img252.imageshack.us/img252/1374/glenrightmlp.jpg


Left MLP:

http://img854.imageshack.us/img854/1341/glenleftmlp.jpg


Rear wall:

http://img195.imageshack.us/img195/7237/glenbackwall.jpg


QRD diffusor:

http://img713.imageshack.us/img713/6926/qrdw.jpg

Wow I need to get these up on our face book page (and our website on the next update). If you are on face book would you mind posting them over on our page?

You are going to want to make those no less then 100mm thick and straddle corners if you want to use them as broad band bass traps. Honestly I would recommend thicker then that if you can. ;)

Given that Reply, I surmise that these are NOT as effective as OC703/705 at the same 1" thickness.:confused:

No, not as good - does that material have a paper facing? Not sure why else the absorption would be so bad at the top end.

703 1" (25mm) on wall 0.11 0.28 0.68 0.90 0.93 0.96
Armaflex 32 mm (1.26") 0.08 0.17 0.51 0.56 0.25 0.24

I think myfipie's comment applies regardless of the material - 4"+ and air space behind at a minimum for bass trapping.

No, not as good - does that material have a paper facing? Not sure why else the absorption would be so bad at the top end.

703 1" (25mm) on wall 0.11 0.28 0.68 0.90 0.93 0.96
Armaflex 32 mm (1.26") 0.08 0.17 0.51 0.56 0.25 0.24

I think myfipie's comment applies regardless of the material - 4"+ and air space behind at a minimum for bass trapping.

Got it. I don't think there is a paper facing. The website is Armacell.com, and under products, you will find the Armaflex rolls and sheets. There is full description there.

looks like it's going to be Plan A--combination of mineral wool to line the corners where the tower speakers are as I can simply stand them up and use the speakers themselves to hold them in place, and OC703 panels (for rigidity) hung in various wall locations.

Should be better than nothing, which is what I have now...:o

Mineral wool works well for bass trapping, and is usually cheaper then rigid fiberglas - but of course, it takes a different approach to mount.

More volume, too, right?

More volume, too, right?

Do you mean you'd need more volume of mineral wool? My understanding is that that's more impacted by density than the material type - i.e. ~3 pcf mineral wool performs similarly inch for inch compared to ~3 pcf rigid fiberglas. Maybe you meant lighter density, like pink fluffy?

Do you mean you'd need more volume of mineral wool? My understanding is that that's more impacted by density than the material type - i.e. ~3 pcf mineral wool performs similarly inch for inch compared to ~3 pcf rigid fiberglas. Maybe you meant lighter density, like pink fluffy?
Yeah, that's it. :o

Docj,
do you have any photos of your space you're willing to share? would assist with recommendations on placement and approach -

Docj,
do you have any photos of your space you're willing to share? would assist with recommendations on placement and approach -

Actually, I will likely snap some digital pics this weekend to post here. The only reason that I haven't done so already is because I am having a carpenter come and lower the mantle shelf above my fireplace (gas, and NEVER even turned on) so that I can mount my Sharp 70" LED above it.
This will, of course, change my speaker layout and therefore my acoustic treatment placement as well.

I will likely go today to buy a bundle of mineral wool panels to have ready, and then get whatever else I need once the room is rearranged.

Well, I got a 6-pack of 2'x4x1.5"', and a roll of burlap to cover it...

HATE the mineral wool. $30 for the panels,and $60 for the burlap = lessoned learned about the mineral wool.Too floppy and easily torn/damaged.

I'll end up keeping the mineral wool for odds and ends, and getting some 703 instead.

Well, I got a 6-pack of 2'x4x1.5"', and a roll of burlap to cover it...

HATE the mineral wool. $30 for the panels,and $60 for the burlap = lessoned learned about the mineral wool.Too floppy and easily torn/damaged.

I'll end up keeping the mineral wool for odds and ends, and getting some 703 instead.

Yes with mineral wool you really do need to use a frame when making panels, but can be nice when cut into triangles and stacked in the corners.

A couple of my corners can only be 24" face corner traps, due to space limitations. Using the Whealy calculator, I tried a few different depths. A 24" face corner trap has a maximum depth of 24 inches (if sound were to enter at a very oblique angle almost parallel to the large 24" face). But that's only at one point. At two other points it has has 17", 8", and 6" of depth, etc. [EDIT: Removed mean and average calculated depth stuff]

So I decided to graph the absorption curves for several low bass frequencies, by inputting into the Porous Absorber Calculator the depth in mm of each half inch slide: 24", 12", 11", 6", etc. for each of seven frequencies.

http://www.ebigpicture.com/images/absorb-chart-5k_rayls-pretty.png

http://www.ebigpicture.com/images/absorb-data-5k_rayls.jpg

They may be a stupid question but I used this DIY method to make some cheap acoustic panelling:

http://www.amateurhometheater.com/diy/acoustic_panels.html

I used pretty much the same duct board. Obviously, fiberglass isn't good for you and every time I handled it, there is usually a slight irritation if it comes in contact with skin.

Now that the project is done and the panels are up, I'm beginning to worry that this may not be good to breathe in and if there are any asbestos type concerns. I know it would be a huge waste of time and money if I take these down and throw them out but health is first. I'm assuming that because they are covered in speaker cloth, they should be fine.

Any re-assurance or warning bells?

They may be a stupid question but I used this DIY method to make some cheap acoustic panelling:

http://www.amateurhometheater.com/diy/acoustic_panels.html

I used pretty much the same duct board. Obviously, fiberglass isn't good for you and every time I handled it, there is usually a slight irritation if it comes in contact with skin.

Now that the project is done and the panels are up, I'm beginning to worry that this may not be good to breathe in and if there are any asbestos type concerns. I know it would be a huge waste of time and money if I take these down and throw them out but health is first. I'm assuming that because they are covered in speaker cloth, they should be fine.

Any re-assurance or warning bells?

I didnt use fiberglass for this reason.

I didnt use fiberglass for this reason.

http://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/347314-comparative-safety-rockwool-fiberglass-organic-fibers-review.html

So....get rid of it???

That double sided tape is going to mean some re-painting as well.

http://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/347314-comparative-safety-rockwool-fiberglass-organic-fibers-review.html

So blue jeans and newspaper shouldn't be in our homes but metal slag and glass fibers are ok because they will break down.

Is the fact that the the surface of the fiberglass has been spray-glued (to fix to the speaker cloth) and is fully covered by speaker cloth make any difference?

Using the Whealy calculator, I tried a few different depths. A 24" face corner trap has a maximum depth of 24 inches (if sound were to enter at a very oblique angle almost parallel to the large 24" face).

Good stuff but
When you straddle the corner it is much more effective then what you posted. I did a quick test of our lab/test room with 8 Monster traps. 3 corners floor to ceiling and 2 on the back wall. Pretty much follows the results we got from Riverband Lab when we tested there. Which shows a great deal of absorption below 100 hz. Note I would want to put in even more treatment but it is pretty close to a 10 db window which is pretty impressive with a great deal of improvement at 67hz.

http://i227.photobucket.com/albums/dd269/glennkuras/freqresponse.jpg

Is the fact that the the surface of the fiberglass has been spray-glued (to fix to the speaker cloth) and is fully covered by speaker cloth make any difference?

fiberglass is a porous material - it works by converting kinetic energy of the soundwave traversing through the series of porous ducts within the insulation into heat (friction). by coating the face of the insulation with a spray or glue, you are blocking the porous holes, restricting flow through the absorber - yielding unexpected results (reflection due to impedance change). you do not want to use spray or glue to coat the face of the insulation to bond fabric. maybe a small dab of 3M spray in the corners...

Good stuff but
When you straddle the corner it is much more effective then what you posted. I did a quick test of our lab/test room with 8 Monster traps. 3 corners floor to ceiling and 2 on the back wall. Pretty much follows the results we got from Riverband Lab when we tested there. Which shows a great deal of absorption below 100 hz. Note I would want to put in even more treatment but it is pretty close to a 10 db window which is pretty impressive with a great deal of improvement at 67hz.

http://i227.photobucket.com/albums/dd269/glennkuras/freqresponse.jpg

I'm not sure what you're saying/showing. That 8 Monster traps with better performance in a room, versus one theoretical slice of 24" fluffy at 60 Hz?

I don't know if it matters, but using the same calculator, with a 4" thick material of 16,000 rayls (is this approximately the gas flow resistivity of a Monster trap?), with a 15" gap (the longest dimension air gap to the wall corner using a 2 foot-wide trap that isn't tapered to fit snug to the edges of the corner), I get .53 absorption coefficient at 60 Hz.

If the trap was had tapered edges to fit snug into a corner, then the longest dimension of air gap would be 17". Switching to 10,000 rayls yields .69 absorbtion.

So blue jeans and newspaper shouldn't be in our homes but metal slag and glass fibers are ok because they will break down.

:confused:

fiberglass is a porous material - it works by converting kinetic energy of the soundwave traversing through the series of porous ducts within the insulation into heat (friction). by coating the face of the insulation with a spray or glue, you are blocking the porous holes, restricting flow through the absorber - yielding unexpected results (reflection due to impedance change). you do not want to use spray or glue to coat the face of the insulation to bond fabric. maybe a small dab of 3M spray in the corners...

Unless there is air gap on the back, does it make difference if sound waves hit glue or wall to reflect back? Also, if it is just meant for high frequency absorber instead of basstrap, the material should absorb all of it by the time it reaches back right?

I just want to clarify if the reason is not valid.

Is rockwool same as pink stuff? I read from localhost127 posts that it is best to absorb/pass waves.

Is rockwool same as pink stuff? I read from localhost127 posts that it is best to absorb/pass waves.

No, its not the same - pink stuff is made of fiberglas, rock wool (a.k.a. mineral wool) is made from stone fibers. Pink fluffy is lower density than most mineral wool (although I'm sure there are different densities available of both, just speaking of the most common stuff).

Unless there is air gap on the back, does it make difference if sound waves hit glue or wall to reflect back? Also, if it is just meant for high frequency absorber instead of basstrap, the material should absorb all of it by the time it reaches back right?

I just want to clarify if the reason is not valid.

if no air gap and the panel is flat against rigid boundary, then it will not make a difference. but by not utilizing an air-gap, you are eliminating your "free lunch".

what is your definition of a "high frequency absorber"? in the specular region, the lower frequencies have longer wavelengths with inherently more energy content. thus, attention for broadband panel absorbers generally needs to be with regards to the lower end of the specular region.

if no air gap and the panel is flat against rigid boundary, then it will not make a difference. but by not utilizing an air-gap, you are eliminating your "free lunch".



With air gap it makes sense. Regarding air gap, I have question. If super chunk bass trap is made with oc 703, does it make difference if 24 inch deep oc 703 vs 12 inch oc 703 and 12 inch airgap? Since oc 703 is cheaper, it is easy to make 24 inch bass traps to stand stable.

Also if volume remaining constant, does filling pink stuff for the same volume more effective than oc 703?


what is your definition of a "high frequency absorber"? in the specular region, the lower frequencies have longer wavelengths with inherently more energy content. thus, attention for broadband panel absorbers generally needs to be with regards to the lower end of the specular region.


I meant panels for first reflections need to be high frequency absorber. I remember absorption coefficient for 4 inch panels for high frequencies is close to or equal to 1. In this case, by the time sound reaches to the back, I thought they would have been absorbed.

I meant panels for first reflections need to be high frequency absorber. I remember absorption coefficient for 4 inch panels for high frequencies is close to or equal to 1. In this case, by the time sound reaches to the back, I thought they would have been absorbed.

so, you're referring to specular reflection absorbers, NOT merely high frequency absorber. the specular region extends down to ~250hz (ignoring room dimensions for simplicity) ... why are you so concerned with HF frequencies of which have little energy content to begin with? that's the entire point behind using appropriate thickness - with focus on the lower specular region of which has longer wavelengths with inherently more energy content! ... of which also are generally more "off-axis" than the higher (more directional) frequencies.

For non-specular bass, like 120 hz, should we consider it to always be "normal" to the surface of an absorber (and likewise every surface of the room),
or is it considered to still have propagated from the location of the loudspeaker and thus has an angle?

And for higher frequencies of diffuse sound fields (which I hear you need a larger room for), does one consider those to always be normal, or do you consider them to be hitting absorbers / diffusers from every angle normal and oblique, because to be diffuse they must be bouncing around from hundreds of different angles?

For non-specular bass, like 120 hz, should we consider it to always be "normal" to the surface of an absorber (and likewise every surface of the room),
or is it considered to still have propagated from the location of the loudspeaker and thus has an angle?

And for higher frequencies of diffuse sound fields (which I hear you need a larger room for), does one consider those to always be normal, or do you consider them to be hitting absorbers / diffusers from every angle normal and oblique, because to be diffuse they must be bouncing around from hundreds of different angles?

there is no reverberant (diffuse) sound-field in small acoustical spaces. hence why absorption coefficients via reverberant chamber are not directly relate-able (but give good indication between performance of materials measured within the same setup). this is why normal incidence (impedance tube) is preferred.

the PAC most certainly has limitations.

Does anyone in here have real world experience with fiberglass vs. roxul? I know most people around these parts are of the opinion that roxul is just not worth it....and the stats back it up. However, the people that I do know that used it (contractors and friends) say that it is worth it and there is a noticeable difference between the two. Any thoughts?

Of course I'll be using the other sound isolation methods as well, but people seem to love this roxul safe n sound stuff (and the cotton stuff) for sound barrier applications.

Does anyone in here have real world experience with fiberglass vs. roxul? I know most people around these parts are of the opinion that roxul is just not worth it....and the stats back it up. However, the people that I do know that used it (contractors and friends) say that it is worth it and there is a noticeable difference between the two. Any thoughts?

Of course I'll be using the other sound isolation methods as well, but people seem to love this roxul safe n sound stuff (and the cotton stuff) for sound barrier applications.

Ditto, on the Roxul, I was wondering the same thing...

I see the term "small" and "large" acoustical spaces/rooms frequently used. Is there a ballpark ft/3 range when talking about small vs large?

John

Does anyone in here have real world experience with fiberglass vs. roxul? I know most people around these parts are of the opinion that roxul is just not worth it....and the stats back it up. However, the people that I do know that used it (contractors and friends) say that it is worth it and there is a noticeable difference between the two. Any thoughts?

Of course I'll be using the other sound isolation methods as well, but people seem to love this roxul safe n sound stuff (and the cotton stuff) for sound barrier applications.

Besides other material, i use the roxul for some bass traps and like it. The traps seem to do the job, at least for my ears. I don't have any room caliberation device such as omni mic or rew just plain 60 year old ears. I really should get one.

I see the term "small" and "large" acoustical spaces/rooms frequently used. Is there a ballpark ft/3 range when talking about small vs large?

John

Concert Hall = large
Anything in a home = small

The one paper I have seen that defines it said a small acoustic space is anything under 3,800 square feet and oddly didn't define the ceiling height. (Assuming 8 foot ceilings that's almost 30k cubic feet -- of course that would be a strange feeling room -- ie, any room of 3800 square feet is almost sure to have a ceiling higher than 8 feet -- which means the cubic volume is even larger.)

Thanks. I'm about 3600 ft/3 with 8.5 ceilings.

Does anyone in here have real world experience with fiberglass vs. roxul? I know most people around these parts are of the opinion that roxul is just not worth it....and the stats back it up. However, the people that I do know that used it (contractors and friends) say that it is worth it and there is a noticeable difference between the two. Any thoughts?

Of course I'll be using the other sound isolation methods as well, but people seem to love this roxul safe n sound stuff (and the cotton stuff) for sound barrier applications.

This thread is focused on acoustic treatments (in the case of absorption, fiberglas or other porous materials mounted in the room, not inside the walls behind drywall), whereas I believe your question is about soundproofing (fiberglas or mineral wool inside the walls behind drywall). You might have better luck posting a separate question, where you can get replies from experts on soundproofing / theater construction (Ted White, Dennis Erskine).

This thread is focused on acoustic treatments (in the case of absorption, fiberglas or other porous materials mounted in the room, not inside the walls behind drywall), whereas I believe your question is about soundproofing (fiberglas or mineral wool inside the walls behind drywall). You might have better luck posting a separate question, where you can get replies from experts on soundproofing / theater construction (Ted White, Dennis Erskine).

whoops, thanks

Thanks. I'm about 3600 ft/3 with 8.5 ceilings.

Yes, anything in a domestic setting is gonna be a "small room" in terms of acoustics. In your case, make your room ten times as big and you are getting our of the small room space. But that'd be one room that is larger than even a McMansion :D

The distinction between a Large Acoustic Space (LAS) and a Small Acoustical Space (SAS) is not arbitrary.

In fact it has a mathematical definition developed by Dr. Manfred Schroeder with important ramifications as it defines limits whereby large acoustical space acoustical principles - as it sets limitations on those generalizations that most encounter in standard textbooks. The understanding of this important distinction was also pioneered by the principles of Bolt, Beranek and Newman.

The common generalizations that most are familiar have significant limits in a small acoustical space - in many cases not having any validity and requiring the use of a significantly modified subset of acoustical rules.

Relating this concept to the environment that folks are concerned with here - namely the Small Acoustical Space (SAS), , one can re-write what was originally presented in terms of the "large room frequency", F sub L, to solve for the volume that delineates a SAS. Note that F sub L is not a fixed rigid value, but rather it denotes the transition region, much like the Schroeder critical frequency, Fc, that delineates the distinction between modal and specular behavior regions.

Fundamental to the distinction is the ability of a Large Acoustical Space, unlike the SAS to support a statistically diffuse reverberant sound field. This ability is frequency dependent, with increasingly larger volumes required to support reverberant sound fields at lower frequencies.

Thus, using the critical frequencies for the various uses, one can determine the minimum volume required for LAS acoustical principles to apply, and conversely, the limits at which SAS acoustical rules apply.

The frequency extent required for speech support, 80 Hz, requires a volume of ~35, 313 ft^3 to transition into a LAS.

For music extending to 30 Hz, the required volume becomes ~251,116 ft^3, and
for music extending to 20 Hz, the required volume becomes ~565,000 ft^3.

Put another way, think that for a room simply supporting speech at 80 Hz, with 8 foot ceiling, the room itself must be larger than ~4375 ft^2! ...Larger than most large houses! And for music to 20 Hz, a room with 8 foot ceiling must be a minimum of ~70,625 ft^2 or almost 18 - 4,000 ft^2 houses!!!!

As should be rather obvious, NO one here is coming close to dealing with a LAS. And it is important to note the distinction and the very critical limitations and necessary differences when one attempts to translate what they see at a LAS theater to their SAS home listening room!

And thus, no one should be employing statistical math models and reverberant sound field calculations in their SAS. Rather than homogeneous reverberant soundfields, one is dealing with a regionally variant mix of localized modal behavior as well as locally variable specular behavior requiring localized measurements and analysis with such tools as the waterfall/cumulative spectral decay (CSD) for modal behavior and the Envelope Time Curve (ETC) response for specular behavior.

Acknowledging the distinction between the two models is critical to the application of the proper acoustical rules that govern such spaces. And the acknowledgment of this distinction is one of the critical developments that define the quantum leap in acoustical understanding that has been ushered in by the introduction of time domain measurements over the past ~40 years.

Thanks! That is the Wikipedia quality summary. Awesome.

thanks dragonfyr.

I need an advice on what I should do.
I currently have a 2" X 2 x 4 panel (JM814) straddled in the back corners of the room on the floor for bass traps.

I just acquired 2 4" x 2 x 4 mineral wool panels that I want to use for bass traps.

Should I

1. Add these 4" in front or behind the 2" panels I already have to make them 6"?

or

2. Should I put them on top or below the 2" panels so that the area covered will be floor to ceiling?

BTW, I plan to fill the space behind the panels that are on the floor with fluffy insulation put inside a plastic bag.

Thanks for the help.

thanks dragonfyr.

+1. Thanks.

1. Add these 4" in front or behind the 2" panels I already have to make them 6"?



or

2. Should I put them on top or below the 2" panels so that the area covered will be floor to ceiling?

BTW, I plan to fill the space behind the panels that are on the floor with fluffy insulation put inside a plastic bag.

If you plan on filling behind the 2" panels then I would not put the 4" panels in front them. Instead straddle other areas of the room. FYI 2" alone straddling the corner is not enough and make sure the 4" panels (and the 2" panels) do not have any kind of solid backing on them. If they do then they will not work.

Thanks for the help.

or




If you plan on filling behind the 2" panels then I would not put the 4" panels in front them. Instead straddle other areas of the room. FYI 2" alone straddling the corner is not enough and make sure the 4" panels (and the 2" panels) do not have any kind of solid backing on them. If they do then they will not work.

Thanks for the help.

Thanks Myfipie. I appreciate that. They don't have any backing. I will do like you said.

I live in kent wa.
I have bass traps, and framed panels. Free to anyone that wants them.
PM me.

I live in kent wa.
I have bass traps, and framed panels. Free to anyone that wants them.
PM me.

PM sent.

:confused:

That's what the article you linked stated. Cellulose or ground up newspaper is bad persay but metal slag or rock wool isn't.

Just curious about the difference and benefit of doing super chunk in a corner vs just hanging a panel.

I am sure it has been discussed before, but I thought to start a fresh discussion on the matter.

Been here (http://forum.studiotips.com/viewtopic.php?f=8&t=536&sid=76dffe152218f775d179ed1bbb728311)?

The conversation was about safety and not everything you just wrote which leaves me baffled why you wrote it.

LOL!

You need to go back and read the thread!

The one where I mentioned I went with greener material other than fiberglass and he linked me to a article about the safety of rock wool, fiberglass and cellulose? Never mind.

What studies are you basing your statement that newspaper or cotton is more dangerous than fiberglass when enclosed of course in a fabric?

What studies are you basing your statement that newspaper or cotton is more dangerous than fiberglass when enclosed of course in a fabric?

There was no such statement made. Please cite.

Maybe you added on the part about being enclosed?

dragonfyr - what is your "day gig?" :)

dragonfyr - what is your "day gig?" :)

With a post like he provided, either a Occupational Health and Safety dude or excellant "Google Researcher" :D

Dragonfyr,

Thanks for the info - very interesting. I did make my acoustical treatments with cotton based material due to the 'non-itchy' nature, but still made them outdoors as they are still dangerous fibers to inhale as you noted (I have a 5yo son, so don't want him to inhale the fibers). Just as a side note, my grandfather died from sever emphysema due to long exposure to cotton fiber inhalation. So I agree, all materials, including natural, have to be handled with care as to reduce any type of fiber inhalation.

I had a very difficult time getting my corner acoustic foam (auralex lenrd) to stick.. the problem I had was that at certain points, the freaking corners weren't "square" , so the things wouldn't sit flush and therefore the glue wouldn't bond.

Ouch.. after spending quite a while and TONS of glue , and making my walls look like crap (I hope I never have to take these down, on one corner I even tore up the drywall enough to see the brown backing), I ended up simply nailing the things down , one nail per corner.. seems to work well, but not sure if there's any detriment to this type of attachment.

What does everyone do? Attach them to backing boards? Glue, glue, and more glue?

Ivan,
I've seen people use really long straight pins on the out side corners. Also, because I'm an Auralex dealer - I'm wondering are you using the tube glue or spray adhesive?

Also - did you try the temp tabs in your setup?

Also, if anyone here needs a recommendation on placement of Auralex product in their space please PM me.

Ivan,
I've seen people use really long straight pins on the out side corners. Also, because I'm an Auralex dealer - I'm wondering are you using the tube glue or spray adhesive?

Also - did you try the temp tabs in your setup?

Also, if anyone here needs a recommendation on placement of Auralex product in their space please PM me.

Essentially, that's what I ended up doing.. the nails are thin and basically function like long pins. I can even reposition them slightly with little force.

Hopefully that will hold and not damage anything :) Who knows, maybe the glue has cured and adhered by now. I won't even try to find out though.

Got them to stay up? Leave them alone..

PS. I was using Loctite power grab caulk. Couldn't get the Auralex glue from Amazon on a reasonable delivery time. (earliest was the 20th) This glue I used says it's safe for foam.. we'll see.

<snip> ... thus, we generally apply a reflective membrane to the corner bass traps such that some mid-HF specular energy is reflective to preserve energy within the room. you can use 6mil plastic to wrap your corner bass traps in ... as bass traps do not need acoustically transparent fabric like the broadband panels do.

I'm relatively new here and have been reading through the most recent pages of this thread - what a great source of information!

I'm in the planning stage creating my corner bass traps for my theater (see signature link) and have a question about the "reflective" warp for corner traps. My wall-hanging panels were covered with a breathable curtain material that I picked up from WalMart and they seem to work quite well. For the corner traps, would it be appropriate to use a "blackout" drape, or similar lined curtain? Or should I track down some 6mil plastic (not sure where I would find it in relatively small quantities)?

Thanks!

Eric,

Welcome! We've interacted over at the Cult,..good to see you've found this treasure trove of info. Where in your room will you be adding the bass trapping? If it's front wall/corner, tricky requirements wrt addressing SBIR/boundary interaction, yet retaining whatever dipole rearward energy characteristics that you want to maintain. I've not experimented much w/dipoles, and their interaction w/the front wall,...however I know it's critical.

Also, I'm not sure of the details above your ceiling, but you've likely got quite the potential for significant LF trapping/damping above the ceiling. You've got bass trap potential across all 12 interior corners.

btw; your room is approx the same as mine, ie mine @ 25'x13'x8'.


Good luck and again,..welcome

Hi Foh,

Thought I recognized your moniker as I was reading back through this thread. The bass traps will go in the back of the room in both of the back corners - floor to ceiling. On my theater page, if you click the picture of my theater it goes to a page where you can see a front and rear panorama of my room.

I was going to build 24x24x36 stackable "superchunk" triangles in each corner. I'll make a ~4ft tall triangle trap and stack a ~3ft triangle trap on top of that and fill them both with triangles of R-19 stacked up. I was wondering about adding 6mil plastic to the front of it (found some at McMaster) or just using a heavy light-blocking drape to wrap the whole thing. I don't know how comparable these two items would be...

I was also thinking about getting some Roxul or fiberglass to put in the space between the ceiling tiles and the bottom of the floor joists across the entire back of the theater. The "dart" tiles in the middle of the room (strange triangle looking relief to them) each have one layer of 1/2 regular drywall just resting on top of them to keep them from rattling around from the huge sub. The perimeter tiles are different because they needed to be cut. The material that the tiles are made from is relatively thin and is very lightweight. It is possible that just filling the 12" or so above them will make a nice bass trap...

I'll have to do some sound measuring for sure.

Eric

Thanks, dragonfyr! I'll pick up some plastic from Walmart, then. Since you indicate that up to 1/8" MDF can be used as well, this makes me think that space in the back of the room above the plastic ceiling tiles will also work well as a bass trap. Overall, then, I'll be able to line both back corners from floor to ceiling AND the entire ceiling/wall edge as well!

One more noob question (sorry if this was addressed earlier - I haven't made it through the entire thread): Does the plastic for the corner bass trap only go on the front exposed edge of the triangle trap? Or, do you wrap all three sides in plastic?

Thanks!

Thanks for the additional details! I'll start with making movable traps in the rear of the room. One of the corners has a door that I need to use from time to time, thus portability is a key factor here. Since I imagine it would be difficult to move a single trap that went floor to ceiling, I figure I'll make two and stack them one on top of the other.

I was going to make a 3D triangle: a wood plate on top and bottom and threaded rod to connect them. After I stack one or two layers of fluffy insulation, I was going to make a "web" of 24ga wire I have laying around to keep the stack from sagging over time (same as the orchard netting). I'll just wrap it around the threaded rod and this will hold up the next layer. I'll attach the front plastic and then wrap the whole thing in fabric (thanks for the tip on flame retardant!). When it's done, all that you will see is a giant "sandwich" with wooden top and bottom boards and the fabric in the middle. Should look pretty clean and neat when its done.

Due to the layout of my room and speaker/lighting positions, I'm not sure how easily I can add traps to the front corners. I'll have to see how much improvement I get from the traps in the rear of the room.

My original REW reading (with no EQ) looked something like this (ignore the scale on the left side- I didn't have things properly set up yet). My current response curve looks much better, but I'd like to improve things without using so many filters and such large dB corrections.

http://www.facstaff.bucknell.edu/esantane/movies/origrew.jpg

Below is my current response curve, but it takes a lot of EQ to get there. The added EQ makes the BFD clip earlier than I would like, makes it necessary to turn down the LFE channel out from my preamp (to something like -13dB), and makes me run my EP4000 amp at full tilt.

http://www.facstaff.bucknell.edu/esantane/movies/IBOutput.jpg

I'm hoping bass traps will allow me to get better response without 1) needing some much EQ, 2) needing to turn the LFE out channel down so far, and 3) needing to run the amp at its max gain.

you should also be generating the waterfall plot to view LF decay times (within the modal region).

I want to throw out a random question. How much resistance bass trapping do you think is required to tame a +10dB peak at 50Hz? By that I mean how thick and how much square footage. Is it even possible? Ignore for the moment that such a trap may (or may not) over damp other frequency regions.

Obviously this is a question based on my own room, but I'm curious what the opinions would be in a general way. I suspect the answer is that no amount of trapping would "solve" a room peak of that magnitude and frequency center.

I'm pretty sure the HT room that I'm in the process of framing is going to have serious dead spots due to low freq standing waves. Dim 15'WX18'LX8'H.
I'm assuming bass traps are the best solution?

This is going to be a very nice theater trimmed in custom wood etc. etc.. I'm wondering if it is possible to have a built-in bass traps in the corners that can be hidden - or at least be inconspicuous. I’m not trying to have an acoustically perfect room, but I want it to be very good – clear dialog, respectable dynamic range yada yada yada…

It is in a basement and the 2X4 (16” o.c.) framing is set away from the concrete walls by 2”. I’m marginally concerned about sound isolation so I plan to fill all cavities with fiberglass or mineral wool and use 2 layers of ½” drywall with green glue between on walls and ceiling.

I’ve attached a sketch of the concept I was considering. Will this work or is it way off base? You can see that I’m basically asking if I can use the last stud cavity in each side of a corner as a bass trap. If I do an insulation/MLV/air gap/OC704/acoustic fabric build-up will it work? The end result would be flush with the finished drywall and the fabric would be the same color as the wall paint so it would be very discreet.

Again, this is just about trying to minimize the low freq. standing waves to a point that is very good, not perfect. Please don’t asking me about what freq range I’m trying to eliminate – if I knew that, I would not post this. Also, if you suggest that I hire a pro, you’re too late; my wife beat you to that one.

237548

With a post like he provided, either a Occupational Health and Safety dude or excellant "Google Researcher" :D
Or a self-admitted "blatant plagiarizer":

http://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/347314-comparative-safety-rockwool-fiberglass-organic-fibers-review.html

He didn't post his source. However, localhost did a few pages back:

http://www.avsforum.com/avs-vb/showthread.php?p=21589699#post21589699

Craig

.....

And below are a few studies of which I am blatantly lifting from another report on the subject.
....

The following is a short (and by no means exhaustive) list of a few blatantly plagiarized sources of studies and their synopsis without proper attribution (as I have a copy of the doc, but I do not have easy access to the source...sorry):
....


Amazing, so the news is that someone FINALLY actually read the post and notices THAT aspect of its content that was explicitly stated no fewer than TWO times??

Congrats!

You can't put anything over on this crowd even when you PLAINLY and REPEATEDLY announce what you are doing!

Now I wonder if anyone will actually bother to read it for the actual point of the post!

The irony is that I do not work for OSHA, but my credentials in acoustical physics far exceed the erroneously posited background in material safety! But that fact is sure to simply cause confusion on this site...

:rolleyes:

Did you miss the words "self-admitted"? BTW, I read it when localhost posted the link. That's why I recognized the SELF-ADMITTED plagierism.

A small elaboration on Dragonfyr's point about high mass boundaries for modal distribution and lower mass interior boundaries for a better specular environment:

1. In non-sound isolated residential basement rooms, it is not unusual to see modal response more indicative of the foundation walls rather than interior room dimensions. That is not necessarily a bad thing; but, does call for acoustic measurements before making gallant attempts at bass trapping.

2. In the typical residential environment where sound isolation is desired, physical constraints and sound isolation requirements can combine to make the high mass/lower mass approach challenging; but not impossible. I've pulled a couple of examples as nothing more than food for thought.

In the end, you will have modal response issues to solve and the combination of approaches selected should be mindful they don't "suck the life" out of the room.

Did you miss the words "self-admitted"? BTW, I read it when localhost posted the link. That's why I recognized the SELF-ADMITTED plagierism.

Again, the irony is that it was NOT actually "plagiarism" at all! That term was used as hyperbole.

As, per plagiarism.org (http://plagiarism.org/plag_article_what_is_plagiarism.html):

"According to the Merriam-Webster Online Dictionary, to "plagiarize" means

* to steal and pass off (the ideas or words of another) as one's own
* to use (another's production) without crediting the source
* to commit literary theft
* to present as new and original an idea or product derived from an existing source."

I did NONE of the above.

The source was dully credited and acknowledged. I simply mentioned that I did not have the URL or author's information for the source at my disposal. I only had an archival copy of the document - which was indeed credited however inspecifically and it was certainly not passed off as my own!

So while I may use the label "plagiarism" self-referentially in a tongue in cheek fashion in the form of hyperbole, others might instead simply mention that I did indeed accurately reference the material as another's contribution.

I liberally use litote, hyperbole and self-deprecating humor. But I am a bit more sensitive when others repeat it out of context and represent my actions as the literal embodiment of that which was originally an exaggeration.

But I am a bit more sensitive when others repeat it out of context and represent my actions as the literal embodiment of that which was originally an exaggeration.

Hmmm, maybe that's what needs work so when your chain is yanked you can ignore the yanker. ;)

Your posts are very interesting and informative even if I don't completely grasp the scientific roots. And even knowing what to cut and paste from other posts requires an understanding of the subject matter. Besides, This is not an academic environment and you are not here to publish your works, so "gathering" from other sources copacetic. IMO. :)

Jeff

Thanks for the reply. There's a lot of information to digest and I want to get to all of it in time. However, if you don't mind let me focus on my original question:

Hmmm.

The problem is MUCH more complex than that.

First, using velocity based porous absorption to damp LF energy is extremely inefficient.

You see, porous absorbers are near useless when placed at low velocity regions near boundaries where the velocity goes to zero. Conversely, porous velocity based absorption is maximally effective at the quarter wavelength where the velocity is maximal.

Just considering that a 50 Hz wavelength is ~22.5 feet long, the quarter wavelength spacing where velocity is greatest is 5.6feet from a boundary! It is there that a porous absorber featuring an optimal acoustical impedance would be ideally placed for maximum effectiveness at 50 Hz. (And remember that here we commonly hear the response that a 2" thick panel is 'prohibitive'!!!)... This should also hammer home the fact that porous 'panels' applied to massive boundaries, however fancily conceived, are NOT significantly effective for LF modal control.

In fact, to put things into perspective, that is why simply for broadband panels, whereby that to which we are actually referring is NOT LF absorption but absorption sufficient simply to control specular behavior ABOVE the modal frequencies from ~300-400 Hz and up, require a minimum of the appropriate 4 inch thick porous material spaced 4 inches from the boundary - effectively moving the absorptive surface 8 inches from the boundary! And those are NOT LF bass traps! But ironically they are generally far more substantial than most imagine being sufficient for more demanding modal control!

I want to focus on velocity trapping for now, simply because I agree with you when you say the design and construction of pressure based trapping is *very* tricky to get right. Indeed, I have attempted it several times in the past with virtually zero success.

So I understand the theory behind the 1/4 wave distance, but I would counter-submit two other pieces of information:

- Just because that is the placement for maximum benefit, does not mean it's the minimum placement required to have some effect, right?

- for example if you look at the absorption coefficients for 2" materials, they are always at least somewhat efficient down to 125Hz (.3-.4) and there are engineered products such as the Quest products that are even better still.

Obviously its also dangerous to look at 125Hz performance and extrapolate to an octave lower! But even if a product was only 5% efficient in this frequency range couldn't you be successful if you had enough of it? And if you put some kind of thin membrane in front to reflect the highs you would not be in danger of overdamping these frequencies.

Further, my question was not meant to restrict 2" thickness - what about 8"? 12"? 16"? This could readily be accomplished behind a screen wall for example.

Thanks

I got a calibrated mic from Dayton, hooked it up via my pre-amp, and ran some REW sweeps.... and realized I don't quite know how to interpret these charts.

Here are the stereo mains, run full range, measured from the listening position.

I know room correction could improve this, but I'm curious to see what I can without that. I have 4inch fiberglass at the first reflection points on walls, ceilings and 6 inch of fiberglass 2 foot tall panels all across one floor/wall "corner".

dragonfyr,

So lets say I were to put 48 square feet (8' wide x 6' high) of 16" thick fiberglass behind my screen, spaced another 16" from the back wall - do you think that alone could do some real damage to a large 50Hz peak?

I have, in the past in another room, attempted some floor-to-ceiling superchunks in all 4 corners similar to what you describe (2' along each wall) and it hardly seemed to make a difference from a measurement point of view.

I got a calibrated mic from Dayton, hooked it up via my pre-amp, and ran some REW sweeps.... and realized I don't quite know how to interpret these charts.

Here are the stereo mains, run full range, measured from the listening position.

I know room correction could improve this, but I'm curious to see what I can without that. I have 4inch fiberglass at the first reflection points on walls, ceilings and 6 inch of fiberglass 2 foot tall panels all across one floor/wall "corner".
I am not an acoustician, nor did I stay at a ...

Other than some stuff very low, your decay time looks very short. Does your room sound dead? My decay times are a little longer than yours, and I am looking at replacing absorption with diffusion.

I got a calibrated mic from Dayton, hooked it up via my pre-amp, and ran some REW sweeps.... and realized I don't quite know how to interpret these charts.

Here are the stereo mains, run full range, measured from the listening position.

I know room correction could improve this, but I'm curious to see what I can without that. I have 4inch fiberglass at the first reflection points on walls, ceilings and 6 inch of fiberglass 2 foot tall panels all across one floor/wall "corner".

- measure 1 source (speaker) at a time
- [modal region] - generate waterfall plot 0-300hz to see LF frequency response + LF decay times ("modal ringing")
- [specular region] - generate Envelope Time Curve response for each speaker to identify early arriving high-gain indirect specular reflections
- RT60 times are irrelevant in small acoustical spaces (no appreciable reverberation exists)

Is there an easy way to tell REW to send a test tone to one speaker at a time? Right now, I have only figured out how to send a stereo signal... meaning I have to swap wires for each speaker...

I am not an acoustician, nor did I stay at a ...

Other than some stuff very low, your decay time looks very short. Does your room sound dead? My decay times are a little longer than yours, and I am looking at replacing absorption with diffusion.

Not dead, but I too have wondered about diffusion and have some panels I will eventually try out.

I just bought 6 24"x24"x7" Skylines and plan on replacing my rear wall absorption. I will try to do some before/after measurements.

Is there an easy way to tell REW to send a test tone to one speaker at a time? Right now, I have only figured out how to send a stereo signal... meaning I have to swap wires for each speaker...

It can be done if your computer has an HDMI output - you can use ASIO4ALL drivers and select which HDMI channel to output to in the Preferences section of REW.

Here is a thread from the HTS forum where I was shown how to do it:

http://www.hometheatershack.com/forums/rew-forum/54840-any-way-generate-sound-center-surrounds.html

In measuring only the two front speakers, I feel that something critical is missing from the analysis: the center channel.

We keep saying the center is so important for home theater, where majority of on-screen voices, music, effects come from. Not knowing how it's doing wth crossover, eq, modal responses, Envelope Time Curve, etc. seems to be missing an important part!

I say center "channel" because for those with a phantom center, they should look at how a mono signal is performing, which is at greatest risk for comb filtering / modal peaks & valleys by virtue of sending the same signal to two speakers.

Thoughts?







Is there an easy way to tell REW to send a test tone to one speaker at a time? Right now, I have only figured out how to send a stereo signal... meaning I have to swap wires for each speaker...

Thanks dragonfyr. I think I'm going to give it a try - its pretty cheap to buy a couple bags of insulation and pretty easy to make up some faced frames.

Regarding pressure treatments, Dennis has actually given me plans for one, but I want to explore whats possible with velocity treatments first because of the relative ease of design and construction.

I want to return to your original reply and this comment:

Combine that with the fact that EQ as a LF tool should NOT be used to attenuate more than ~3 dB of a peak, and you can see the obstacles with which one is faced. (Anything more and I can pretty much guarantees a severely 'out of whack' gain structure that imposes far more issues on the reproduction of sound than does the modal issues they are trying to address! ...Especially given the constraints of consumer level amplification compared to most pro level amplification with its substantially increased duty cycles... )

How does an EQ'd signal look any different to the amplifier? Assuming the source signal of course could already be of some arbitrary frequency response, and already contains all manner of studio processing.

I would say that if you restrict EQ to 3dB there's no point - you can't really hear that little difference.

Thanks!

Regarding pressure treatments,...

http://www.amazon.com/Acoustic-Absorbers-Diffusers-Theory-Application/dp/0415471745/

It can be done if your computer has an HDMI output - you can use ASIO4ALL drivers and select which HDMI channel to output to in the Preferences section of REW.

Here is a thread from the HTS forum where I was shown how to do it:

http://www.hometheatershack.com/forums/rew-forum/54840-any-way-generate-sound-center-surrounds.html

I have HDMI output on the computer and ASIO4ALL available, so I will review that thread and give it a try.

Nathan, we can help you. But help us by posting the REW .mdat file so that we can convolve the frequency response into the various views and window them accordingly.

And as local observed, we want to drive each source individually with the measurement mic remaining in the EXACT same (reproducible) position for all current and future tests.

And with treatment in place, its difficult to say what can be done, or what original actual issues exist that require treatment and thus to suggest what needs to be done, as we do not have the untreated baseline response to judge. Untreated measurements would be a wonderful addition if the concept does not scare you too badly... We can then determine the effectiveness of the treatments and suggest any additional measures...

And seeing as how REW can be used in any number of configured audio topologies it hardly seems work all the effort to attempt to configure it to a specific configuration when it is simply but one possible topology out of many when its easier and quicker to simply manually change the input relative to the device you want to test.

Okay, once I get the measuring of individual speakers working, I'll post the mdat file. I assume the one for the stereo pair isn't as useful, interesting?

Ha, okay I complicated the issue by mentioning a phantom center. Never mind that.... it's just my trying to include the edge cases.

The point was: the center is extremely important in home theater, and I read here about most people just measuring the stereo fronts, ignoring the speaker they'll be using the most.

I did so too: reading the REW guides I just measured the front two, with and without sub, individually, etc.

But recently I've been assessing the center, and since EQ is always a compromise, I've chosen to sacrifice some smoothness in the stereo fronts in favor of center frequency smoothness and better integration with the sub.

But recently I've been assessing the center, and since EQ is always a compromise, I've chosen to sacrifice some smoothness in the stereo fronts in favor of center frequency smoothness and better integration with the sub.
How did you do that?

For the record, I measured the stereo fronts first because

1) it was easiest with the default REW setup
2) I listen to two channel music, and when it comes from the turntable, it's without EQ -- so in addition to the usual "get your room as right as possible with treatment before restoring to EQ" wisdom, I want to get my room as right as possible without EQ since sometimes I listen without EQ (but only in stereo).

By isolating each (front) speaker, they are able to determine if any first reflection point treatment is needed.

How did you do that?

I didn't like some or the decisions my old crappy MCACC was making for the center, so I made some tweaks.

And I chose a higher crossover so I could EQ more in the BFD, weighting the center more. Width modes affected my two front L and R differently from the C, since they're at different distances from the side walls.

I used DPL-ii music mode with a narrower center-width so that REW would go to the center, since the old receiver doesn't have HDMI. :(

Well, I look at the waterfalls, too, which shows the time domain. And as I'm experimenting with bass traps, I'm looking at the center. And the waterfall shows less ringing after EQ and bass traps.

Whether it's frequency-domain (looking at the result of the time domain problems due to modal issues) or anything else, the point is that when I read most people's (for multi-channel, not stereo) description of the channels/speakers they're analysing, they neglect the center. Not to mention the importance in choosing the best locations for listening positions and and subwoofer(s) placement. As you know, a simple modal calculator only goes so far when we're talking about trying to model a real room.

Actually, a cumulative spectral decay is not a time domain response, although it does show a series/sequence of frequency displays.
OK, it involves the added dimension of time, but it's not "time domain." Gotcha.

And may I politely but firmly make one more fundamental suggestion - move beyond the flatland of the frequency response!
...
Unfortunately all it does is reinforce the need to generate individual measurements in the time domain.

So you read that I'm suggesting that not enough attention is paid to measuring the center, you tell me that I should abandon the "flatland of frequency response" and use the time domain. Then...

And in the modal region where the energy is essentially minimum phase, the time domain is not of much use - hence why we use the frequency response and the waterfall display.
Then you say that one should be using the frequency response, aka "flatland."

And to expand, you are unfortunately totally ignoring the specular region that specifically determines imaging, localization, intelligibility, and spaciousness and colorization of the direct signal - the very aspects that your explicitly stated concern regarding the center channel (as well as all he rest) - while instead focusing on the modal behavior!

No, I've started playing with the ETC too. I just didn't mention it.

Unless you're saying, "Stop looking at any frequency response or waterfalls for any of the speakers and the sub," then doing so is still part of the analysis, education, and calibration process that people are going to undertake with something like REW.

I've been learning about the comb filtering, learning about the modal problems in the room, learning about the effects of positioning listeners and sound producers in my room, learning about the effects of bass traps, learning about the ETC and trying the blocking method and string method to isolate where reflections are coming from...and I'm sure I'm still leaving something out that you will jump on eg "you're totally ignoring the important..." etc. All the while missing the point, or choosing to address the extraneous and incomplete parts of my point.

And while modal behavior is important, it is the wrong tool for the job you have specifically identified as the focus of concern.
My focus of concern here is to point out that acoustical analysis and treatment of the center is not given the attention it deserves. Aside from Nathan who was concentrating on stereo music, many home theater enthusiasts read guides and method posts that only include the front-left and front-right and neglect the center. That's all I'm saying. If I left out of this post, "...and I made sure the speakers were facing towards the listeners and not the walls..." it's not because I didn't do that, it's because I just left it out.

And the answer is NOT to artificially raise the crossover frequency in order to employ more EQ!!!! Above ~80 Hz the response is no longer minimum phase and EQ is NOT correct! This is not an error, but a mistake.
So, to be clear, all filters on the LFE/summed bass channel above 80Hz are a mistake?

In raising the crossover frequency, I also allow higher frequencies to be produced from my subs, where I get a smoother response. Lower the crossover from 100Hz to 80Hz, or 50Hz, and the response was way worse.

I expect a lot of things to change as I employ bass traps that at least fix the upper bass frequencies, as I've already seen it do while positioning bags of fiberglass around. I hope to use less EQ, I hope to be able to reposition the speakers with less regard for modal response and more for imaging. And I'll see what I can get away with using porous absorbers. Luckily, my room's walls aren't too rigid.

The tool that is appropriate for your stated concern is the ETC response.
My concern in working with REW and the center is inclusive of modal behavior and specular behavior.

I'm confused - how can the ETC graph be used to identify and correct frequency response issues from 80Hz to, lets say, 300Hz? Surely you are not saying that by treating the identified specular reflections it can correct room response down to these frequencies?

Thanks for the alignment paper. I actually have looked at group delay when adjusting distances and subwoofers phase in the receiver to get the best response. But it was crude trial and error. The paper show using the impulse response to actually see the delay and adjust accordingly... nice!

And the center speaker has little to do with modal behavior, and as a result, neither the frequency domain nor the waterfall is the tool that will do the heavy lifting.


I'm not sure if you're saying none of the five or seven main speakers has little to do with modal behavior, or specifically just the center doesn't?

Per best practice in a comprehensive approach, EQ is the very LAST step done After ALL of the modal and specular room issues are treated via a variety of methods. And it is then used as sparingly as possible...Unlike the various room correction packages that rely almost solely on it as the first (and essentially only) technique.

This is what I''ve always heard WRT improving a room's sound.

1) Speaker position
2) Listener position
3) Acoustical treatments
4) Electronic correction

Except for subs, though, speaker position is difficult to change as they are usually where they are because of other factors. Listeners are usually where they are because of other factors as well. That brings us to treatments, something that many overlook or eschew because of aesthetics. And that leaves electronic room correction.

I'm not trying to rationalize it, this is reality.

I sure wish we would figure out what we want to address!:D

It feels like when we mention specular issues, that the subject shifts to modal issues, and when the topic is modal issues the issue becomes specular.
I believe it is you shifting the topic to something I left out to beat your drum (which I agree is a fantastic drum :) ).

This is what I started with:

In measuring only the two front speakers, I feel that something critical is missing from the analysis: the center channel.

We keep saying the center is so important for home theater, where majority of on-screen voices, music, effects come from. Not knowing how it's doing wth crossover, eq, modal responses, Envelope Time Curve, etc. seems to be missing an important part!

I say center "channel" because for those with a phantom center, they should look at how a mono signal is performing, which is at greatest risk for comb filtering / modal peaks & valleys by virtue of sending the same signal to two speakers.

I mentioned how I feel the center is ignored, you glom on to the phantom center part. I have highlighted the part in red that contributed little to the point, that I never ever should have mentioned.

Next I say:

Ha, okay I complicated the issue by mentioning a phantom center. Never mind that.... it's just my trying to include the edge cases.

The point was: the center is extremely important in home theater, and I read here about most people just measuring the stereo fronts, ignoring the speaker they'll be using the most.

I did so too: reading the REW guides I just measured the front two, with and without sub, individually, etc.

But recently I've been assessing the center, and since EQ is always a compromise, I've chosen to sacrifice some smoothness in the stereo fronts in favor of center frequency smoothness and better integration with the sub.
For convenience, I've colored in green the part where I underscore the point that I was focusing on.

When I say I'm measuring with and without the sub, that suggests I'm looking at modal issues, and not specular issues, right? I certainly didn't intend to imply that ETC is lame and specular issues don't exist.

So then you shift us into ETC, implying that someone's making a mistake in looking at modal.

Simply put, you measure EACH source independently with respect to the time domain.

And may I politely but firmly make one more fundamental suggestion - move beyond the flatland of the frequency response!...
So now you've launched off about how we should move beyond frequency response to time domain.
When I mention waterfalls, then you say that frequency response and waterfall is appropriate for modal work.

The bouncing around is due to your picking on something that I didn't mention or didn't clarify or use the best language to describe. But continually neglecting to address the point.

I think you're concerned with the main platform of your posts, which is to not try to EQ non-minimum phase problems, to treat modal issues with modal solutions that are best tailored to their behavior (pressure traps for lower bass where porous absorbers fail, etc.), and to treat specular issues with specular solutions. Which is fine, but you keep trying to fit those lessons into responses to my thesis which is that the center speaker shouldn't be ignored.

You finally get around to addressing that by saying that the center isn't part of the modal issues. Which I understand to span the lower frequencies near the crossover of ALL the speakers, and the subwoofer's frequencies.

And then I asked for clarification about your statement, and you reply last with...


The center speaker by virtue that it is a full range speaker typically reproducing voice probably has little impact on the modal frequencies - at least compared to the subwoofer!
Yes, the center channel typically produces voice, but it also contains all sorts of music and effects.

And yes, it doesn't contribute as much to the modal frequencies as does the sub. And neither does the front-left. Or the front-right. Because they're probably crossed over at 80Hz.


But in any event, it is what it is and will contribute accordingly based upon whatever energy is produced in its bandpass.


Yep, it'll contribute. So, what were you suggesting when you said that the center doesn't contribute to the modal response? That it doesn't contribute as much as the front left and right because it contains LESS music, and thus we should leave it out?

ALL of the full range speakers will be individually evaluated with an ETC. And from this the various energy wavelets will be evaluated and high gain anomalous returns will be resolved into their vector paths and points of incidence and the appropriate surgical treatment determined depending upon their function in the overall response model.
Good, we're including the center here. We agree about that, and people are doing themselves a disservice if they neglect it in the ETC measurements.

First, the ETC is not used to correct frequency response issues. It is used to address time domain issues with respect to the superposition of high gain interactive specular signals. By addressing these causal issues the destructive results of superposition are negated and the derivative effects upon the frequency response cease to exist.

Well, aren't you simply describing a different means to the same end? If ETF identifies time domain issues, and by correcting them the frequency response issues "cease to exist", then you are correcting frequency response issues in a manner of speaking. So my question is still the same - if I applied room treatments to eliminate all high gain specular reflection signals, can that successfully eliminate the derivative effects on frequency response even down to 80Hz?


You might want to read the section in the REW tutorial regarding minimum phase

Here is my Excess Group Delay graph for one speaker one listening location:

https://lh4.googleusercontent.com/-3XL5rBO5x1E/T0K9yJNR1yI/AAAAAAAADG4/F7yd6Y1U7uo/s800/excess_gd_right.jpg

Does it mean that, with the possible exception of around ~110Hz, this could be considered minimum phase to almost 300Hz? or at least to that blip around 190Hz?

By the way, the tutorial suggests that that response I see around ~110Hz is probably a room null, but in fact what I have centered around that frequency is a large, wide peak (from around 90Hz to around 130Hz). So is EQ a valid tool for me at these frequencies?


But the larger issue is that your priority seems to be the reverse of best practice. Per best practice in a comprehensive approach, EQ is the very LAST step done After ALL of the modal and specular room issues are treated via a variety of methods. And it is then used as sparingly as possible...Unlike the various room correction packages that rely almost solely on it as the first (and essentially only) technique.

Not at all! Obviously EQ is a last resort, but I still keep it as a tool in the toolbox. As pepar said, most people are constrained from a design point of view as to where speakers and seats can be. Most people are also contrained from a monetary point of view :) when it comes to room treatments.

Cheers

First, there was an ongoing discussion before you jumped in with stuff about "phantom center channels" (the only thing i could figure was an allusion to the apparent virtual image created by spaced sources) and something about some proposing the omission of speakers when measuring the ETC response.

People "jump in" here all the time. There are usually at least two parallel discussions going on at any given time.

You've never heard the term "phantom center" before? It's pretty common practice around AVS. I was using it as it's commonly used. Yes, that's what I meant, not using a center speaker, but for multi-channel source that contains center channel content. Again, that was a minor part of what I was talking about. And you addressed that, but not the point. I thought of this when I saw Nathan's post, but later he clarified he was dealing with stereo music.

No, I didn't propose the omission of speakers when measuring ETC. Read what I wrote again. I said that people often do omit the center, and I proposed that they should not.

Best practices for performing comprehensive acoustical measurements for both modal and specular issues haven't changed significantly in over 25 years that I have been actively doing them...
Right, but I wasn't saying that YOU in particular was doing something wrong. Did you think I was saying, "Hey, acoustic experts, scientific journals, and professional theater designers: you forgot something!" ?

A perfect example of what I'm talking about his here: http://www.avsforum.com/avs-vb/showthread.php?p=21562732#post21562732
Okay, so I ran my first couple REW measurements, and have played with positions, sub delay (distance), Large/Small, treatments, crossover points, bass/treble trim, subs only, subs and mains, etc. ... The purple line is my L/R alone fullrange. (Set to large with subs off)

He refers to the front-left and front-right speaker as "Mains," suggesting they're the two important speakers. He doesn't get into ETC, but I wouldn't be surprised if that, too, stuck with the front-left-right speakers.

I could find another 1000 examples at AVS and Home Theater Shack. From what I've seen, the MAJORITY of people omit the center. This seems really strange and wrong to me, at least for multi-channel purposes. I think this is borne out of the same old-school mentality that has newbies buying giant floor-standers and a tiny center for home theater. Does anyone ELSE know what I'm talking about? Or am I completely wrong here, and you see most people using REW with their center?

I thought it was worth mentioning and asking about. Sorry to interrupt your flow.

This is like being in a fun house of mirrors - where everyone each interprets what is said as being directly and individually 'aimed' at them! :D :rolleyes: :D

Welcome to teh internetz :)


While the ETC is the response that shows you where and what all the cars whizzing around the track are doing sufficient for us to determine the actual dynamic status of the situation sufficient to make and access modifications as necessary.

So this is the part where I (and I'm sure many others) are having difficulties making the mental leap. I am certainly familiar with ETC response graphing, but my practical experience is limited is using it to identify early (<20ms) high gain reflections, in order to improve imaging. How exactly can the ETC response be used to identify issues that manifest as gross frequency response issues, and how can it be used as feedback as you are attempting to correct those issues? More detail would be appreciated here, as long as its not a link to a 500pg textbook containing theory from first principles :)

My first suggestion is to STOP running back to the flatland fixation with the frequency response!

The fact is that few of you even know the actual baseline response of the speakers you are using anyway, let alone can distinguish between the FR of the source and the FR of the speaker-room system.

And if you know that the time domain behavior is causal, why then do you need to focus on the derivative perspective?

You can't simply say "ignore frequency response" - that's what we hear! If I listen to my system and its one-note bass, I want that to go away. Full Stop. It may be semantics to say you correct it by solving the time domain issues, but the *symptom* is the frequency response aberration, and I want the symptoms to go away.

Look, I'm buying in to what you are selling - But I still have the same question, what am I supposed to *do* with an ETC graph?

The frequency response is a static snapshot of the derivative pileup caused by many factors of which we have absolutely no insight taken after the accident has occurred - affording us no causal information or means by which to possible modify the behavior to avoid the problem.

While the ETC is the response that shows you where and what all the cars whizzing around the track are doing sufficient for us to determine the actual dynamic status of the situation sufficient to make and access modifications as necessary.

brilliant - i'll be "borrowing" this analogy if you don't mind !

Fine - you are telling me there is no spoon :) I am not sure yet. I will refrain from using the F word here forward in the interests of preventing further conversational roadblocks.

Nevertheless, how many times do I need to ask (and how much more politely!) : How do I use the ETC curve to identify the time domain psycho-acoustic "unpleasantness" in the room, and how to I use that information to even begin to treat it? Is it as simple as finding all high-gain reflections sub-20ms, treating them with broadband treatment, et voila? I suspect not!

Let me use a different analogy ... he wants to know how to fish and you keep telling him, in probably the most elaborate technical terms I've ever seen, that there are fish and the method he's presently using won't catch them.

dragonfyr,

Here's the problem then. You seem to have a lifetime of information locked up inside of you, but to us you are talking Greek (or Latin, or perhaps just Esperanto). If the only answers are "Go read these three texts, the exam is next week closed book" then you will get almost 0% take-up from anyone here. And I suspect that is what is frustrating you.

The reason why someone like Dennis is highly respected around here is that he will spend the day beating you around the head with concepts you don't understand, and then the next day he will come back and explain those same concepts in a way that is of *practical* value to those of us with real world constraints and only one undergraduate degree :D

I continue to read your postings to find the nuggets of information I can actually do something with.

Putting aside all that, could you at least comment on whether or not I interpreted my excess phase graph from REW correctly?

Cheers

Let me use a different analogy ... he wants to know how to fish and you keep telling him, in probably the most elaborate technical terms I've ever seen, that there are fish and the method he's presently using won't catch them.

Yes, precisely. Further, that other people have figured out how to fish, fishing is a known solved problem and has been since the 60's, and you don't really want to catch trout, if you aren't out there catching deep-sea tuna there's really no point :D

Seems like a good time to re-post this - ;)

What measurements do I need to do to determine if I need more SSC corner bass traps? I have this one that I thought was telling me I could use more ...

Single measurement location (at MLP)

http://www.peparsplace.com/storage/Baseline_Aud_On_s.jpg

I meant to comment on that before - it strikes me as unusual that your response is that strong down to 16Hz with no sign of a roll-off. I'd be a little skeptical that that measurement is correct?

No, you want a one size fits all specific answer to an amorphous ill formed question with guarantees that the suggestion will function to spec without any incumbent responsibility to actually learn what is happening. And that it will not only address objective standards, bu that it will also satisfy whatever personal subjective preference you prefer.

I don't think I asked for that at all - if there's one thing that makes it difficult to have a conversation here its that you are continually jumping to (IMO erroneous) conclusions about our motivations for asking questions.

You and localhost are very passionate about using ETC curves to solve room problems. I want to know more in a way that is practical and doesn't require me to delve into acoustics textbooks or bust out my own control theory texts (all this talk of poles and zeros - I barely understood it the first time around in school)

I am simply asking for more information about the process, and how to use the tools we have at our disposal.

I meant to comment on that before - it strikes me as unusual that your response is that strong down to 16Hz with no sign of a roll-off. I'd be a little skeptical that that measurement is correct?
Yes, my REW measurements show it nearly flat to 16Hz and then dropping like a stone below 16Hz. Here is an earlier sweep of the subwoofer with REW, though this is a single pair collocated in the front while the Omnimic graph was with two collocated pair (front/rear) ..

http://www.peparsplace.com/storage/center_aseq1_on.jpg

And here's one with the previously maligned Audyssey room correct OFF ... (note and compare the time domain parts of this and the previous graph)

http://www.peparsplace.com/storage/baseline_Aud_off_s.jpg

And as has happened earlier on this forum, we jump from the simple introduction of a tool to the demand for a fully formed final certified design guaranteed to satisfy all concerns - including the wife who wants no visible treatments or speakers in the room.
I missed those posts; were they deleted? :confused: ;)

So, since you now have a hammer, you now want me to tell you, in very simple terms, exactly how to build "a house'.

Not even! I am asking for things like which side of the hammer should I hold, and should I use it to drive nails or screws :D

We can either talk in generalities or we can talk in specifics. I would be very happy to talk specifics, post REW graphs and mdat files if you like - but I have asked now several times for comment about the excess group delay graph that I posted but you don't seem to want to talk about that.


And then, I can present a slightly simpler modified template that is both suitable and can be reasonably and practically achieved in almost any room. And in doing the aforementioned we will see how the approach can result in an improvement in imaging, localization, intelligibility, lack of coloration, and, depending upon the nature of the specific room, an increase in the sense of spaciousness. But realize that this will also assume the meeting of certain fundamental criteria such as symmetry, properly constructed walls featuring highly resistive walls, and sufficient space to implement the design. I can also explain, on occasion as the opportunities arise, how various compromises can influence the result as well.

That sounds like great information, as long as you realize the sorts of constraints most people have in working with existing residential spaces. But personally I really want to know more about *my* space, and to do that I want to understand how to interpret ETC graphs.



And then I will predict, just as has happened previously on this as well (as another) very forum, that there will again be a few folks who will then take issue with the approach as it does not necessarily address their or yet another particular and undefined subjective preference (in terms of their preferred acoustical response or 'style of house') or another application, be it a critical listening room, studio, home theater, music practice room, board room, lecture hall, or loading platform of the subway - all of which vary in their response and all of which can employ a variety of subjective variance.

Well of course this will happen - like I said, welcome to the internet! Embrace the chaos :)

That sounds like great information, as long as you realize the sorts of constraints most people have in working with existing residential spaces.

physics, psycho-acoustics, acoustics, etc - aren't going to modify themselves based on your "constraints" wrt residential spaces. that is probably your first step into the understanding of acoustics.

What measurements do I need to do to determine if I need more SSC corner bass traps?


why would you assume that "corner" traps are going to cure all of your LF/modal issues? are the other boundaries irrelevant to superposition with the direct signal? why does one assume that LF absorption only takes place in the "corners"? porous absorbers are broadband absorbers. ideally, an absorber should be designed such that it is effective at the trouble (actual MEASURED) frequency. in small spaces, broadband absorption is necessary, but for the more troublesome issues - more fine-tuned 'treatments' will be required (not just in the effectiveness of the treatment itself, but the placement as well!).

physics, psycho-acoustics, acoustics, etc - aren't going to modify themselves based on your "constraints" wrt residential spaces. that is probably your first step into the understanding of acoustics.

This entire paragraph is wholly irrelevant to almost all of us here. To those whom it is not irrelevant, they hire somebody to build the room for them.

Don't let the perfect be the enemy of the good.

No. Local may know which they are...

But the past 2.5 years have been dominated by exactly the same calls we now receive (as well as cries from 'a few' lost souls who decried the ETC response even being made available to "non-professionals" :rolleyes::rolleyes: ), with the results that I would rather not see repeated and am not interested in again partaking. The mechanics are objective. I am not interested in additional debates over the subjective preferences of various flavors of ice cream.
I have to ask - do you have dual degrees in acoustics and drama? ;)

Can you post the mdat file(s)?
I have not previously saved measurement files, only graphs. I see now that I need to save the former as well so that more analysis can be done.

Was the sweep a full range sweep, or a band-limited sweep?
For the record, may I suggest making all sweeps full range. The device itself or post processing widowing can always function to restrict the results if necessary.
The Omnimic graphs are with and without Audyssey (XT 32 w/Pro calibration) room correction. It was mono signal driving L&R analog inputs with bass management, so a 2.1 configuration. I don't recall what the swept frequencies were, but IIRC it was limited to what is displayed.

The REW was subwoofer only swept from 5Hz to 200Hz.

Is there any EQ applied. or is this a purely 'acoustic' response?
If EQ is applied, it would be beneficial to rerun the baseline sweeps with it turned off.
One of the Omnimic measurements was with no EQ/correction. The others had whatever I was using at the time; my Audysey versions have advanced over the years.
Off hand, it looks pretty good. Around 70 Hz there seems hints of a null typical of an 8 foot ceiling, and the null ~140 Hz can be a confluence of both the 2nd harmonic as well as perhaps the coincidence of multiple modal resonances. But unless there is substantial resonance, you look OK
The bouncing around above 150Hz where the mains take over is what I wanted to correct with more traps. Room is nominal 13 x 21 x 8. Here is what's behind my false/screenwall -

http://peparsplace.com/images/studiotips_superchunk_20.jpg

why would you assume that "corner" traps are going to cure all of your LF/modal issues? are the other boundaries irrelevant to superposition with the direct signal? why does one assume that LF absorption only takes place in the "corners"? porous absorbers are broadband absorbers. ideally, an absorber should be designed such that it is effective at the trouble (actual MEASURED) frequency. in small spaces, broadband absorption is necessary, but for the more troublesome issues - more fine-tuned 'treatments' will be required (not just in the effectiveness of the treatment itself, but the placement as well!).
I assume nothing.

Design limitations preclude using any treatments for modal interactions other than corner traps. The range reproduced by my multiple subs seems well-behaved. It is the region above that to Schroeder that gets wooly. I have some 2" OC 703 panels at first reflection points, and ill-conceived wall carpet below ear level. I also have six Skylines that I am going to swap for the rear wall absorber.

Jeff

This entire paragraph is wholly irrelevant to almost all of us here. To those whom it is not irrelevant, they hire somebody to build the room for them.

Don't let the perfect be the enemy of the good.

so what if it is irrelevant to many of us here - it is simply the truth.
if you think we can modify the behavior of physics/acoustics just because the bulk of us are constrained to residential small acoustical spaces, then there is little left to say here.

it is absolutely astounding the difference in communication between some of the studio forums where many users are absolutely thrilled to engage in such a conversation (to learn and explore) - and this forum where is it endless bickering with very little substance (and more cries for "on size fits all" solutions). this is not a personal statement to anyone, just my own personal observation.

I assume nothing.

Design limitations preclude using any treatments for modal interactions other than corner traps. The range reproduced by my multiple subs seems well-behaved. It is the region above that to Schroeder that gets wooly. I have some 2" OC 703 panels at first reflection points, and ill-conceived wall carpet below ear level.
Jeff

your statement was - what measurements are needed to determine if you need "more" corner traps. what happens when you run out of corners?

I also have six Skylines that I am going to swap for the rear wall absorber.

why not utilize the skylines in front of the LF rear wall absorbers? (granted seating distance to diffusers are appropriate)

it is absolutely astounding the difference in communication between some of the studio forums where many users are absolutely thrilled to engage in such a conversation (to learn and explore) - and this forum where is it endless bickering with very little substance (and more cries for "on size fits all" solutions). this is not a personal statement to anyone, just my own personal observation.

Are you really surprised? Really? Consider the audience for once - here we are all concerned with building a great room to entertain guests and enjoy being in. There is a balance of priorities and ideal sound is only one of them. In a studio there is no such compromise - the *only* goal is sound quality.

I really don't understand why you find this so difficult to grasp.

And for what its worth, I think a lot of people here are willing to put in a lot of legwork (contrary to your belief that everyone wants a "one size fits all" solution) but again there are almost always constraints on whats possible. Is it your conclusion that its not worth it to do *anything* in this case?

The classic example are the so called 2" treatments. You basically say its 8" or its crap. Dennis produces designs subject to this constraint - are you saying his rooms sound like crap?

But you and a few others seem determined to generate drama. And very few who are serious to learn about the physics - in fact, specifically and actively stating their desire to avoid having to do exactly that as others demand simple practical 'answers' to overly generalized imagined spaces.

As far as 'are additional treatments necessary', who knows. Measurements made with tools like Audyssey engaged tell us little and obscure what is happening acoustically. And the excessive use of EQ can easily create such behavioral anomalies in other regions of the passband.
Having a head full of knowledge is not anywhere near being able to actually help people with it. I'm sorry that I don't measure up, but I am tired of being lectured to. So I am going to withdraw my ill-formed request for help.

No. You don't get it. It is not my job to "realize the sorts of limitations most people have".

I hope you don't consider participating here a job - you certainly aren't getting paid for it.

If you don't want to consider the audience that's fine - but then all your effort is likely not to be appreciated and I would recommend you don't bother.


But one might quickly realize that porous absorption for LF modal issues is neither the only treatment option, nor is it the most effective. And this is precisely a case where a greater understanding of physics quickly affords one more options that, while a bit more complex, are also more effective.

A good case in point - I think many people here realize that porous absorption for LF modal issues is not the most effective. But pressure traps are very difficult to build and even harder to prove you built them right (fixed the right problems rather than making others worse). So they are often discounted. Don't mistake this for ignorance on our part necessarily.

your statement was - what measurements are needed to determine if you need "more" corner traps. what happens when you run out of corners?
I have plenty of unused corners.

why not utilize the skylines in front of the LF rear wall absorbers? (granted seating distance to diffusers are appropriate)
I would like to tweak (and improve) what I already have without tearing everything out and starting from scratch. For now, anyway, the false wall cavity's treatment is staying as it is.

Are you really surprised? Really? Consider the audience for once - here we are all concerned with building a great room to entertain guests and enjoy being in. There is a balance of priorities and ideal sound is only one of them. In a studio there is no such compromise - the *only* goal is sound quality.

check the thread title - this is "Acoustical Treatments Master Thread" - not a user's self-created thread based on THEIR room based on THEIR design requirements and THEIR end-response goals.

and the concepts and acoustical models of that of a mixing/mastering studio are directly transferable to that of a critical listening space.

...and in studios there are still compromises, as financials are most certainly a factor.


And for what its worth, I think a lot of people here are willing to put in a lot of legwork (contrary to your belief that everyone wants a "one size fits all" solution) but again there are almost always constraints on whats possible. Is it your conclusion that its not worth it to do *anything* in this case?

The classic example are the so called 2" treatments. You basically say its 8" or its crap. Dennis produces designs subject to this constraint - are you saying his rooms sound like crap?

please quote me where i say 8" or "crap". my statements are with regards to attenuating the broadband specular signal down to the lower specular region OF WHICH with typical speaker designs there will be MORE off-axis energy dispersed of which has LONGER wavelengths of which has MORE inherent energy content. and yet so many wish to "treat" for the HF content with their thin absorbers of which has little energy content and is generally more DIRECTIONAL of which there is LESS energy thrown to the reflection points in the first place!

it was only a few weeks ago you were arguing me with the usefulness of the mirror to identify reflection points (and your insistence of treating "all reflection points" - regardless of their incident gain or time-arrival).

im really curious as to what ground you feel you stand on regarding the discussion of acoustics with such commentary.

and your cute little comment that seems to imply i am making ANY subjective statements regarding Dennis' designs is hogwash and a last ditch effort by yourself to stir up absolute nonsense because you lack any sort of effort to adhere to the focus of the subject re: acoustics.

and to think Pepar claimed it was dragonfyr who likes the drama??

I would like to tweak (and improve) what I already have without tearing everything out and starting from scratch. For now, anyway, the false wall cavity's treatment is staying as it is.

depending on what measured issues you are seeing from the rear wall will dictate whether you still need LF absorption there...

will your skylines attenuate the signal to the same lower frequency cut-off as your absorber? do you need further LF absorption of the rear wall phasor? or do you want to combine LF absorption with mid-HF diffusion to provide some energy back into the room?

and why do you wish to use 2D reflection phase grating diffusers vs that of 1D? what was your criteria for making such a decision?

It can be done if your computer has an HDMI output - you can use ASIO4ALL drivers and select which HDMI channel to output to in the Preferences section of REW.

Here is a thread from the HTS forum where I was shown how to do it:

http://www.hometheatershack.com/forums/rew-forum/54840-any-way-generate-sound-center-surrounds.html

Thanks kromkamp and nathan_h for this tip, I downloaded the 5.01 beta REW and ASIO4ALL driver last night, and will see if I can get it to work tonight.

and why do you wish to use 2D reflection phase grating diffusers vs that of 1D? what was your criteria for making such a decision?
A friend didn't need them and sold them to me for $50 each. ;) If I swapped my front wall/ceiling absorbers for diffusors, I would use QRDs.

check the thread title - this is "Acoustical Treatments Master Thread" - not a user's self-created thread based on THEIR room based on THEIR design requirements and THEIR end-response goals.

Check the Forum title - its "Home Entertainment & Theater Builder", not "Studio Builder"


the concepts and acoustical models of that of a mixing/mastering studio are directly transferable to that of a critical listening space.

The *acoustic* goals are the same, but nothing else - how many mixing studios do you know of with a popcorn machine in them?


please quote me where i say 8" or "crap".

If you *really* want me to I'm sure I could. Virtually 100% of your forum posts exclusively recommend using 4" treatments spaced 4" from the wall. You do the math.


it was only a few weeks ago you were arguing me with the usefulness of the mirror to identify reflection points

Yes, as do you here:

http://larchive.avsforum.com/www.avsforum.com/avs-vb/showthread.php?p=21273989#post21273989

I agree with what you say at the bottom of that post - no more no less. I never said using a mirror was the be all and end all.


and your cute little comment that seems to imply i am making ANY subjective statements regarding Dennis' designs is hogwash and a last ditch effort by yourself to stir up absolute nonsense because you lack any sort of effort to adhere to the focus of the subject re: acoustics.

and to think Pepar claimed it was dragonfyr who likes the drama??

I never said I didn't like drama :) but my point is 100% valid - you continually argue that physics does not bend to the will of good aesthetics and practical considerations, and yet Dennis produces designs that do all the time (as I'm sure many other theater designers do). I can't reconcile these two datapoints and I don't think you can either.

Having a head full of knowledge is not anywhere near being able to actually help people with it. I'm sorry that I don't measure up, but I am tired of being lectured to. So I am going to withdraw my ill-formed request for help.

actually, the issue is not with dragonfyr but with you yourself. you are unwilling to put forth the effort and presume acoustics is a simple topic. no one is "forcing" you to learn anything, but if you wish to traverse the rabbit hole that is acoustics, you will need to understand the underlying principles, physics, etc -

yes, you're tired of being "lectured to". just like when dragonfyr went through the multi-page commentary regarding the MISCONCEPTION that diffuse or reverberant sound-field exists our rooms, and so many insisted that they did exist.

and what did you have to say after all of that knowledge was presented on a silver platter?
--> http://www.avsforum.com/avs-vb/showthread.php?p=21284261#post21284261

why would anyone continue to assist you with your questions when you act in such a manner.

I hope you don't consider participating here a job - you certainly aren't getting paid for it.

If you don't want to consider the audience that's fine - but then all your effort is likely not to be appreciated and I would recommend you don't bother.

and to think, dragonfyr has basically given you all of the knowledge on a silver platter - you are just too blind by emotion to absorb it.

dragonfyr,
maybe you should start "charging" - do you think people will think your commentary is more credible if there are dollar signs attached to it?


A good case in point - I think many people here realize that porous absorption for LF modal issues is not the most effective. But pressure traps are very difficult to build and even harder to prove you built them right (fixed the right problems rather than making others worse). So they are often discounted. Don't mistake this for ignorance on our part necessarily.

no - it's just no one wants to put forth the effort because they *think* it is too difficult. i wonder why all of the "home/bedroom studio" forum users are able to take the challenge, but in this forum it is simply a lost-cause and not even worth the attempt.

A friend didn't need them and sold them to me for $50 each. ;) If I swapped my front wall/ceiling absorbers for diffusors, I would use QRDs.

awesome deal on the price.

although i would still prefer PRD over QRD (but my original statement was in reference to 1D vs 2D skyline, not PRD skyline vs QRD)

Check the Forum title - its "Home Entertainment & Theater Builder", not "Studio Builder"

this is the acoustical master treatment thread.

again, you wish to discuss anything but acoustics - and you sure do not have any "authority" on the subject.

The *acoustic* goals are the same, but nothing else - how many mixing studios do you know of with a popcorn machine in them?

please, detail the "acoustic goals". be specific.


If you *really* want me to I'm sure I could. Virtually 100% of your forum posts exclusively recommend using 4" treatments spaced 4" from the wall. You do the math.

yes - i really want you to. please quote me where i say "crap".
and if you actually took the time to understand the lower frequency limits that must be absorbed with regards to specular energy, and how porous insulation "works" or is "most effective", then you too would choose an appropriate GFR/thickness material. but of course, you'll still fail to understand the impact of the speaker response as well as acoustical impedance of boundary - as you have in prior threads. (http://www.avsforum.com/avs-vb/showthread.php?t=1391430)

please quote me?

no - it's just no one wants to put forth the effort because they *think* it is too difficult. i wonder why all of the "home/bedroom studio" forum users are able to take the challenge, but in this forum it is simply a lost-cause and not even worth the attempt.

Well, as dragonfyr said:

Unfortunately their design is more complex and an iterative process, as their inclusion in the system has the effect of modifying the system of which they are a part. Thus while they are not out of the reach of the average person, their design and integration is not a trivial process.

More than a little daunting, to be sure. That being said I'm certainly not diametrically opposed to using them.

actually, the issue is not with dragonfyr but with you yourself. you are unwilling to put forth the effort and presume acoustics is a simple topic. no one is "forcing" you to learn anything, but if you wish to traverse the rabbit hole that is acoustics, you will need to understand the underlying principles, physics, etc -

yes, you're tired of being "lectured to". just like when dragonfyr went through the multi-page commentary regarding the MISCONCEPTION that diffuse or reverberant sound-field exists our rooms, and so many insisted that they did exist.
I would suggest that anytime someone feels the need to post a multi-page commentary regarding any misconception, they should take a pill.

Jeff

again, you wish to discuss anything but acoustics - and you sure do not have any "authority" on the subject.

Not sure you do either - but I wasn't aware that was a prerequisite here.


yes - i really want you to. please quote me where i say "crap".

no problem - I doubt you used that actual word but something similar. Should be a fun project for me to do tonight.


and if you actually took the time to understand the lower frequency limits that must be absorbed with regards to specular energy, and how porous insulation "works" or is "most effective"

You keep saying that as though its not completely obvious that thicker treatments are more effective at lower frequencies - just curious if you don't think I understand that? Because I assure you that I do.

no problem - I doubt you used that actual word but something similar. Should be a fun project for me to do tonight.

oh, yes - changing your tone now since i called you out. you're willing to spend your entire evening digging through my commentary searching for the term "crap" and yet you refuse to take a few brief moments to further your knowledge on the relevant subject of acoustics.

this is representative of the prevalent attitude here. well done!



You keep saying that as though its not completely obvious that thicker treatments are more effective at lower frequencies - just curious if you don't think I understand that? Because I assure you that I do.

thicker treatments do not necessarily mean more effective absorption at lower frequencies. this is over-simplification of porous absorption. i assure you you do not understand this based on your commentary.

thicker treatments do not necessarily mean more effective absorption at lower frequencies. this is over-simplification of porous absorption. i assure you you do not understand this based on your commentary.

Oh good - then it means I won't need to use 4" treatments spaced 4" away from the wall after all! Huzzah!

Oh good - then it means I won't need to use 4" treatments spaced 4" away from the wall after all! Huzzah!

precisely - you ignore (or you are completely unaware) of the other factors that dictate a porous absorbers performance, as thickness alone is not the only variable. hence, you'll generally see the recommendation for thickness relative to a specific material (or more accurately, a material with a specific gas flow resistivity value).

So give me an example of an porous acoustic treatment that absorbs less LF as it gets thicker please.

So give me an example of an porous acoustic treatment that absorbs less LF as it gets thicker please.

do you understand what gas-flow-resistivity means? or do you think "thickness" is the absolute variable that determines the performance of any porous insulation. oye.

http://www.whealy.com/acoustics/Porous.html

Same question. Supply an example please.

there's really no point in going through this exercise with you. you clearly have your mind made up regarding porous absorbers...

Same question. Supply an example please.

porous absorber calculator.
OC703 - 16,700rayls/s (although NASA has tested differently).
increase thickness.
observe.

According to Owens Corning's own specifications, you are wrong. From Bob Gold's site:

703, plain 1" (25mm) on wall 3.0 pcf (48 kg/m3) 0.11 0.28 0.68 0.90 0.93 0.96 0.70
703, plain 2" (51mm) on wall 3.0 pcf (48 kg/m3) 0.17 0.86 1.14 1.07 1.02 0.98 1.00
703, plain 3" (76mm) on wall 3.0 pcf (48 kg/m3) 0.53 1.19 1.21 1.08 1.01 1.04 1.10
703, plain 4" (102mm) on wall 3.0 pcf (48 kg/m3) 0.84 1.24 1.24 1.08 1.00 0.97 1.15
703, plain 6" (152mm) on wall 3.0 pcf (48 kg/m3) 1.19 1.21 1.13 1.05 1.04 1.04

According to Owens Corning's own specifications, you are wrong. From Bob Gold's site:

703, plain 1" (25mm) on wall 3.0 pcf (48 kg/m3) 0.11 0.28 0.68 0.90 0.93 0.96 0.70
703, plain 2" (51mm) on wall 3.0 pcf (48 kg/m3) 0.17 0.86 1.14 1.07 1.02 0.98 1.00
703, plain 3" (76mm) on wall 3.0 pcf (48 kg/m3) 0.53 1.19 1.21 1.08 1.01 1.04 1.10
703, plain 4" (102mm) on wall 3.0 pcf (48 kg/m3) 0.84 1.24 1.24 1.08 1.00 0.97 1.15
703, plain 6" (152mm) on wall 3.0 pcf (48 kg/m3) 1.19 1.21 1.13 1.05 1.04 1.04

why do you stop at 6"? what happens at 30"? 60"? the porous absorber keeps getting thicker, shouldn't it be absorbing lower frequencies more effectively like the blanket statement you made?

the point of this exercise was to attempt to introduce to you the fact that there are more variables than simply "thickness" of a porous absorber.

what do you think happens as you continually increase the thickness of a porous absorber? what happens as GFR increases? what happens if the soundwave can no longer penetrate through the porous holes and thus is no longer converting kinetic energy of the flow into heat? ..and the "absorber" suddenly becomes a "reflector".

again, the exercise will fail because you are utterly ignorant about the complexity of porous absorption and the inherent variables OTHER than thickness.

and revisiting the original statement of which your contention spawned from, you'll notice that the recommendation of 4" absorber w/ 4" air-gap is generally accompanied by a material with GFR or density outlined (eg, this is usually in reference to OC703 (3pcf) or Mineral Wool (4pcf) when giving 4" thickness 4" air-gap recommendation) - as the absorber needs to have a high absorption coefficient based on the lower specular region (250-300hz) as well as taking into considering angle of incidence, speaker radiation pattern, acoustical impedance of boundary, etc.

Don't know and don't care. Probably at 1000" something else happens again. Its outside the context of the conversation. You are being deliberately obtuse.

Newtonian physics aren't accurate either - but if I ask you what time it is the correct answer is not "depends how fast you are traveling"!

Don't know and don't care. Probably at 1000" something else happens again. Its outside the context of the conversation. You are being deliberately obtuse.

welcome to acoustics.

Newtonian physics aren't accurate either - but if I ask you what time it is the correct answer is not "depends how fast you are traveling"!

:)

OK. Let me say it. You guys are all WAY more advanced in your knowledge and expertise on this whole subject that most of us. Heck, I get lost in the long posts about how to do some of this stuff, but I DO appreciate your efforts. It just goes to show how passionate you all are about giving the "right" information (whatever that is). I have been following this thread for quite some time, and I get little golden nuggets that I can easily understand and implement and I plan to use them. My room will be better for it, even without the (to me) complex REW graphing and such.

Maybe, someday, I will try to drive down that road...slowly...and with my hazard flashers on... But I am sure that the further I go down the road, the more I will understand where it is I am trying to get to.

So with that, step back and take this guy's "thank you"....

If you knew what you were talking about you would know that you are not comparing two absorbers, but rather a porous absorber on the one hand, and a hybrid binary amplitude diffuser (BAD) that incorporates about 4 inches of absorption behind a diffusive Galois sequence membrane on the surface!

And simply applying inadequate amounts of absorption (such as the commonly used 2" thick panels you mentioned above) is NOT necessarily better than nothing

I'm doing no such thing. Dennis uses Quest products (well I'm sure not exclusively) which are 2" deep full stop. Are you saying these are not better than nothing?

Cool it with the personal comments guys...

We have already explained the issue.

Heck, even Toole addresses the issue and laments the effective EQing of specular reflections resulting in coloration (in addition to the original issues!).

If they are using the equivalent of OC700 series semi-rigid fiberglass panels, the problem exists.And the specs they quote assume a diffuse incident soundfield - something that does not exist in a small acoustical space.

What you choose to live with is your choice.


And I guess the owner of this magnificent theater:

http://www.avsforum.com/avs-vb/showthread.php?t=1373052

also does not realize that, in fact, his room sounds worse than if no treatments had been applied at all. I hope no one tells him :)

Cheers

My acoustic designer has specified the following for the wall behind my screen :
"Two layers 1" Johns-Manville Coated Insulshield Black or Linacoustic RC (black)
with 3 mil vinyl sheeting between layers."

However I cant find this product anywhere in my area (Vancouver, BC). I looked on the Johns-Mansville website and Rona is one of their dealers, but I called all the local stores and no one has heard of it.

Does anyone know where I can buy this product in the Vancouver area?

Question about acoustically transparent fabric:

Right now I use dark velvet curtains to pull along my side walls to kill some room reflections. But I want to go further and have the ability to make a "black box" in the room. Therefore I'm augmenting my existing curtains with some black acoustically transparent (e.g. speaker grill material) curtains.

In this picture you can see the room. I pull the curtains along the wall and put thick dark brown velvet covering the entire fireplace wall. The opposite room wall gets the same treatment. However, this leaves uncovered the bright wall past the fireplace toward the windows on each side of the room, (with the surround speakers on them) as well as the entire area behind the sofa.

I want to cover the entire area but I DON'T want to deaden the room any more (if possible). So I'm going to add acoustically transparent curtains to cover those remaining spots, including one big curtain that will pull behind the entire sofa (with cut out for projector light).

Can I presume that adding this much "acoustically transparent" material (again, the type used for speakers) this should have minimal acoustic effects? The point is with the amount of velvet I already use on the walls, along with the live portions of the wall, I get a not-too-dead sound. I just want to make sure that using acoustically transparent material to cover the rest of the walls will still keep some "live" surface area.

Opinions?

Thanks.

http://img94.imageshack.us/img94/129/dsc8741.jpg

And I guess the owner of this magnificent theater:

http://www.avsforum.com/avs-vb/showthread.php?t=1373052

also does not realize that, in fact, his room sounds worse than if no treatments had been applied at all. I hope no one tells him :)

Cheers

I think Dennis talks about how most of the treatment in there is diffusion.

...
Sucking the life (aka absorption of early -or otherwise- reflections) out of a room is not at all a best, or better, practice. Diffusion and/or diffraction is an alternative.

I want, if we could, to return to my original question on ETC. you hit the nail on the head here:


There are also secondary issues of pattern recognition useful in identifying how treatments such as absorption, reflection and diffusion appear in an ETC, either for use in analyzing existing behavior or in evaluating where a particular treatment would be appropriate and useful…in other words, 'how' to employ the tool in order to accomplish a specific well defined goal. But there use is only practical only AFTER a specific acoustical response goal has been specifically defined.

This is exactly what I'm after. Unfortunately I have to answer you with another question: What are the parameters that define a specific acoustical response? If I tell you I want it to sound "good" or "accurate" or "pleasing" that is surely not sufficient. And yet if I tell you it's a home theater then surely there are baseline standards that define that acoustical response goal, no?

As someone who has followed this thread since day one, I'd like to make a few comments. This part of AVS is mostly populated with DIYer's and in the beginning I believe this thread provided us with some good, basic design advice, which could be quite easily put into practice with relatively little expense. Those with a sufficient budget would normally employ a professional to do all the acoustic 'heavy lifting'.

More recently the thread has evolved into a much deeper discussion that I believe very few of us have sufficient time, education or experience to follow, and certain participants just don't seem to understand the audience they're talking to.

I would really like to see the thread return to being a source of practical, achievable advice for the average DIYer, trying to get maximum bang for buck.

Cheers,

Knauf, Certainteed, Owens-Corning and others manufacture similar products to the J-M *Coated* InsulShield Black. In your application, Elite, the product specified is (a) going behind an "acoustically transparent" screen; and, (b) will be exposed to the living environment. Other than the statistically similar physical properties, you require a product which is (a) a uniform color of black [noting black is not a color]; and, (b) meets local environmental air quality standards for a product exposed to room air.

The Quest products are not simple sheets of OC700 series fiberglass. They are fabricated laminates of a combination of various fiberglass board, vinyl, and backing products with performance characteristics radically different from a simple 1", 2" or 4" off the shelf fiberglass board. The specifications quoted do not *assume* a fully random incident, diffuse sound field. ASTM testing methodologies have defined the conditions under which the specified testing is to be conducted. Until such time as a series of standardized testing methodologies are codified more appropriate to small acoustical spaces, we have to adapt, overcome, and utilize OTJ practical experience to interpret actual, as built expected performance.

The performance and applicability of any given acoustical material (particularly porous materials) cannot be judged independently. Once such a material is applied to any other material (4" fiberglass applied to 1/2" drywall, attached to 22 gauge, 5.5" steel studs 24" O.C. for example), the resultant is not the sum of the materials ... the behavior is that of an entirely different or "third" material if you will. You cannot ignore the impact of the underlying strata in any series of layered materials and their order of occurrence.

it is not my problem here to solve personal, social, financial, or any other problems that someone may artificially impose upon the issue
None-the-less, personal, social, financial, or any other problems are not "artifical" within the context of the unique individual or specific constraints of any given, individual and specific project. Those "problems" in any given specific project, to the homeowner, are real and must be addressed if only to inform the homeowner, commercial contractor, mix engineer, artist, or studio executive as to how those "problems" or constraints may impact the final result. At some point there must be a convergence of expectations and applied constraints.

Insulshield is 1.5 pcf density so any similar density product should be a decent substitute.

It sure can be a pain finding these products in Canada sometimes...

Insulshield is 1.5 pcf density so any similar density product should be a decent substitute.

Not exactly ... but pretty close. The "coated" part of the J-M product not a pure coating, has a slightly different density and porosity than the straight fiberglass. Let me know what you find locally and I'll check it out for you.

Insulshield is 1.5 pcf density so any similar density product should be a decent substitute.


two different porous insulations with identical density can have differing GFR values.

This part of AVS is mostly populated with DIYer's and in the beginning I believe this thread provided us with some good, basic design advice, which could be quite easily put into practice with relatively little expense.
...
More recently the thread has evolved into a much deeper discussion that I believe very few of us have sufficient time, education or experience to follow, and certain participants just don't seem to understand the audience they're talking to.


I see some progress being made in:
What is the purpose of this forum/thread?
What are the limitations of the veteran theater buff, the theater DIYer hobbyist, and the newbie? How best to interface with him?
What are the limitations of the acoustician? How best to interface with him?

Forums & Thread
I think many of the problems with this thread and forum is what you'd have if you couldn't break out the Sources into separate fora like cable, local hdtv, bluray, etc. Or display devices into LCD, Plasma, Projectors, Expensive Projectors. Or speakers into DIY, subs, etc. Acoustics It's too broad a topic, and it doesn't even have a dedicated forum. There's also "Audio Theory, Setup, & Chat" again, too broad for acoustics.

This particular thread is full of interjections like the one I made earlier, trying to reconcile and emulate designers' methods, bang-for-buck DIY treatments, actual usage of measurement methods, acoustic models, trying to reconcile works like Toole's with other paradigms, and "hey i'm new to this stuff but what do ya guys thing i should do?"

I suggest splitting out theory discussion and help-me threads. And if there are agreed-upon general precepts and critical core concepts, then we need sticky-worthy primers. Until those exist, then the "experts" are in a constant drone of repeating the same forever.

Real World Theater Application of Acoustics
I agree with Mr. Erskine; there are compromises and limitations in applying acoustic science to home theaters. If one doesn't deal with that, then you're just reading, writing, or repeating theory textbooks.

This topic(s) is so much more difficult to grasp and address than "what's the best sub?" threads. But there's something to be learned from there. The newbie there thinks there's one end-all solution for subwoofers. The veteran educates that different subs meet different goals and criteria, and ask, "What are your constraints, what do you want to do?" Without that starting point, it's all theory, or a tug of war of competing solutions to meet different goals, without addressing the real constraints.

So I can appreciate dragonfyr's frustration when people skip that first step of establishing "what CAN I do? what are the different models and their tradeoffs for me, what are my constraints?"

I thought a great step forward were the threads of a few months ago where the different room models were being discussed and people wanted real application of ETC. - Not sure what happened with that...I last read discussion about which models are most appropriate for stereo music, versus for multi-channel home theater. Here's one of the threads: http://www.avsforum.com/avs-vb/showthread.php?t=1366724

Someone needs to write the Room Model Primer

Main classes of models:
Reflection-Free Zone
Live-End Dead-End
Ambiechoic
...
with some variations within each
primary attributes of each (eg LEDE: acoustically-damped "dead" front, suited more for the soundstage and ambiance to be produced by the source material and multiple speakers, with a more "live" and diffuse rear zone that helps to spread out the surrounds' sound field, which enhances ambiance, retains some sound power, and simulates a commercial cinema)
Pros and Cons of each model
What the ETC typically should look like for these models
Levels of attainment for theaters, starting with the no-brainer, critical, bang-for-buck, and low-hanging fruit stuff, progressing to more difficult, expensive, less ROI, but delivering the last 30% of the room model's goals.

There's room to discuss everything here. If we were just limiting it to basic DIY treatments we wouldn't need 291 pages to cover that :)

My point was that people shouldn't get frustrated when they offer advice and people here respond that they are unwilling to go to certain extremes for very valid practical reasons. Doesn't mean they aren't learning or aren't willing to incorporate some of that information into their designs.

What Do Surfaces and Treatments Do to FR?
I read Toole's latest book a while back, but I can't remember if there's good graphics of how the frequency balance changes when reflected from different materials of different absorption characteristics?

It would be edifying to see this.
"I had a flat response coming from one speaker.
THIS is what the response curve looks like coming from this drywall/2" panel/etc.
THIS what my ear will hear."

Achieving Room MOdels
The best diagrams / photos / experiments / case studies on blocking and string method should be reproduced here.

Honestly, the experts would save themselves thousands of hours of retyping the same stuff if they could make this more accessible to laypeople.

Progress from how a bouncing ball indicates the ball's positional translation over time, to how an ETC shows the reflections the impulse hit over time. Relate the ETC to diagrams of a room, to real photos of such a room prior to treatment.

Case Studies
Show us how you found some real problems (the room isn't matching the desired model), measured to find the source of the problem, and tackled that problem with treatment.

(This should be in the room model primer I mentioned above)

Do so in a way that can be...

Minimally applicable for the casual family room (which I suppose is its own model) where low-hanging fruit that fixes the worst problems for a realistic family room model.
Low effort / expense applicable for a dedicated theater room. Under $1,000 of treatment, under 50-100 hours of effort?
Medium effort / expense, where one might get into some diffusion, maybe a pressure trap, some room construction, be willing to sacrifice more room dimensions, etc.
Maximal achievement of the criteria for the room model.


I'm not necessarily addressing the acoustician, or the professional theater designer, but rather anyone who has tackled these issues and likes to help and educate. We have hundreds of theater build threads, where some of these issues are addressed. We have hundreds+ of specific room challenges or DIY treatment construction, but not tackling the room model in a holistic, start-to-completion fashion.

It's like seeing fragments of bird house theory, and bird house painting, and components of the bird house plans, and some of the bird house construction.

Although every room and every user is different, there's still great merit in seeing how others tackled their challenges.

My point was that people shouldn't get frustrated when they offer advice and people here respond that they are unwilling to go to certain extremes for very valid practical reasons. Doesn't mean they aren't learning or aren't willing to incorporate some of that information into their designs.

Right, and that's what I was alluding to when talking about different groups interfacing with other groups.

Acousticians should realize that when someone is asking about a modal issue, it doesn't mean that he's unaware of or hates specular issues and thinks the ETC is lame. Or when choosing to focus on porous traps is unaware that there are other more effective, albeit expensive / difficult methods. Surely I can talk about a consumer sports car without being told that custom-built race cars are more effective. And experts should be sensitive to the real constraint-plagued world of home theaters, or they will forever be frustrated at people's reticence at achieving the entire 100% of a room model, or not implementing the most effective treatment, and we'll never get help we can actually use, and people new to this area are turned off.

Conversely, the veteran should clarify what his goals (room model, specific issue one's trying to tackle) and constraints (effort, financial, aesthetics) are. Pepar has done this by stating what construction & deconstruction he's willing to undertake. Failing to do this is like saying "I want a speaker, which is best?" Without that initial planning work in understanding the models and targets, it's hard to engage in discussion about application.

I also agree with the above in taking issue with being compared to pro studio builders. That's like comparing the DIY home renovator to a professional construction company owner. Or the sports car hobbyist to the race car builder. The home theater is for fun in their home; the GearSlutz user is probably doing this as a business, where the quality of the studio mix output will affect his livelihood. The studio world also has a longer legacy of implementing models. The acoustic models appear to originate in the context of building better studios, although I think a lot of that research has its roots in professional performance spaces (and thus the challenges in translating theory and practice from the large to the small).

Just for reference, when sound conflicts with an object, some of the sound will transfer through the object, and/or be reflected, and/or be absorbed. Any time sound is reflected off an object there will be a frequency and phase shift. Whether or not those shifts are audible or distracting is subject to an entirely different discussion. Anytime you're in a chamber room, auditoria, or shower stall the surrounding environment is affecting what you hear and perceive. That's life. That's they way it is. We humans have adapated very well to living and playing in boxed in spaces. A fine Bosendorfer or Strad will sound different in Carnegie Hall, Mechanics Hall or the Kennedy Center.

Reflection-Free Zone
Live-End Dead-End
Ambiechoic
...

All of these are different approaches to achieve the same goal ... accurate (and pleasing) sound reproduction. In the end, if what you really, really, like is the sound in Mormon Tabernacle or Meyerson Hall ..., well you'll just have to buy the building. :)

Can't I just push the button my AVR to simulate those spaces? ;)

Continuing that thought, is it worth describing again with more detail the kinds of room problems that we do want to fix, and by how much?

As dragonfyr put it, what is the specific acoustical response goal we want to hit for a residential, small room home theater?

There's room to discuss everything here. If we were just limiting it to basic DIY treatments we wouldn't need 291 pages to cover that :)

At 8737 posts and counting, this thread is quite unwieldy - honestly, I think there needs to be a separate forum dedicated to acoustic treatments and soundproofing.

Can't I just push the button my AVR to simulate those spaces?
Yamaha made that rather reasonable approach starting with the DSP-1

At 8737 posts and counting, this thread is quite unwieldy - honestly, I think there needs to be a separate forum dedicated to acoustic treatments and soundproofing.
How to implement and then get that to work though? The Audyssey thread is 50k posts and we periodically gnash our teeth over people not reading the first post, not searching ... basic forum skills and etiquette ... and how a new thread should be started that is dedication to this or that subtopic. And then we all come back to "this thread is highly active, is at the top of the page and people will continue to click on it and ask their question regardless of what other threads are created."

Not saying it isn't a good idea, just tossing out food for thought.

BTW, this discussion is GREAT. Perhaps something constructive will come out of the latest feather ruffling.

Jeff

At 8737 posts and counting, this thread is quite unwieldy - honestly, I think there needs to be a separate forum dedicated to acoustic treatments and soundproofing.

+1 and leave this one for theory banter.

IMO if you have to quote a scientific paper to support your view your probably deep in left field theory territory and of little use to the average DIY HT enthusiast.

I challenge one of the elite folks here to Erskine, Winer, etc. to start a thread focused on the low hanging fruit for DIY HT folks.

Some simple starting points that would get most of us 90% of the way there. I'll bet most will agree on the best starting points. Getting the last 10% is where all the theoretical discussions and differing of opinions convelude the simple things which would make the average HT better.

Continuing that thought, is it worth describing again with more detail the kinds of room problems that we do want to fix, and by how much?

As dragonfyr put it, what is the specific acoustical response goal we want to hit for a residential, small room home theater?

Absolutely! I don't know if it should be here, or in Bigus' thread, or wherever.

The first task is understanding that there ARE different models.
Next is understanding their differences and how that applies to home theater.
Then picking one, which as Dennis is suggesting, may be a more subjective choice.
Last, implementing it to some degree.

Some simple starting points that would get most of us 90% of the way there. I'll bet most will agree on the best starting points.

Yeah, I see people here wanting to know, "What's the stuff that probably applies in 80% of the cases that probably won't do harm, that I don't need to spend 100 hours in planning to determine whether I should implement?"

Maybe porous corner bass traps fall in that category, but your chosen model would dictate what the front corners are doing with mid-to-high frequencies. You can broadband absorb, diffuse, only absorb the bass, etc.

And maybe "lastly after other bass treatment, EQ in modal region those peaks that are consistent for your important seats, where it's minimum phase."

The rest depends on the model, but if we're talking home theater, and not a large choral performance space, I suspect some of the models can be winnowed down due to the use of multi-channel source and speakers providing some of the ambiance, as well as real-world constraints like not being able to cover all the surfaces with diffusors.

The room model thread (http://www.avsforum.com/avs-vb/showthread.php?t=1366724&page=2) ended in January with two pages, last post by kromkamp. It should be continued, maybe with more concerted intent at coming to agreement, rather than disagreement.

The room model thread (http://www.avsforum.com/avs-vb/showthread.php?t=1366724&page=2) ended in January with two pages, last post by kromkamp. It should be continued, maybe with more concerted intent at coming to agreement, rather than disagreement.

Well, four or five posts into that link, I encountered the same lack of respect that just erupted here over the last several days. It's not the thread topic that makes or breaks a thread, it's members not interacting properly with others.

+1 and leave this one for theory banter.

IMO if you have to quote a scientific paper to support your view your probably deep in left field theory territory and of little use to the average DIY HT enthusiast.

I challenge one of the elite folks here to Erskine, Winer, etc. to start a thread focused on the low hanging fruit for DIY HT folks.

Some simple starting points that would get most of us 90% of the way there. I'll bet most will agree on the best starting points. Getting the last 10% is where all the theoretical discussions and differing of opinions convelude the simple things which would make the average HT better.
Here are two posts that get to some basics - I have these bookmarked

http://larchive.avsforum.com/www.avsforum.com/avs-vb/showthread.php?p=17390783#post17390783

http://www.avsforum.com/avs-vb/showthread.php?p=15406068#post15406068

From Bob's post, this always struck me as very basic - "In an otherwise empty/reflective room, studiotips superchunks and first reflection point absorbers are a good thing. In other rooms, your mileage will vary."

+1 and leave this one for theory banter.

IMO if you have to quote a scientific paper to support your view your probably deep in left field theory territory and of little use to the average DIY HT enthusiast.

I challenge one of the elite folks here to Erskine, Winer, etc. to start a thread focused on the low hanging fruit for DIY HT folks.

Some simple starting points that would get most of us 90% of the way there. I'll bet most will agree on the best starting points. Getting the last 10% is where all the theoretical discussions and differing of opinions convelude the simple things which would make the average HT better.

I think Mr Winer;s book may help many people:
http://www.ethanwiner.com/book.htm
http://www.ethanwiner.com/expert_cover.jpg

I've always wanted to write a book about audio, and a few years ago I started making notes about what I would include. As it happens, a major publisher of technical books approached me in early 2011 after seeing my hour-long AES Audio Myths video. So I submitted a proposal for my book, The Audio Expert, which they quickly approved. I worked on the book literally non-stop since then, and finally finished the first draft in late November. All 26 chapters were then sent to black belt technical editor Mike Rivers for his comments and suggestions, which I applied. (Thank you Mike!) I then did one final "polish" pass on the entire book, and sent it to the publisher January 8. The copy editor and layout department are now putting the book into its final form, then I'll review it one last time before it goes to the printer.



This is a very comprehensive "reference" type book covering all aspects of audio, with many practical as well as theoretical explanations. It's written for people who want to understand audio at the deepest, most technical level, but without needing an engineering degree. The Audio Expert explains how audio really works in much more depth than usual, using common sense plain-English explanations and mechanical analogies, with minimal math. It's presented in an easy to read conversational tone, and includes more than 400 figures and photos to augment the printed text. You can view the Table of Contents now, which includes a list of all the videos that total more than 3-1/2 hours running time.

However, this book goes beyond merely explaining how audio works. It brings together the concepts of audio, aural perception, musical instrument physics, acoustics, and basic electronics, showing how they're intimately related. It also describes in great detail many of the practices and techniques used by recording and mixing engineers, including video production and computers. This book is meant for intermediate to advanced recording engineers and audiophiles who want to become experts. It's definitely not a "Dummies" type book for beginners!

One unique feature is explaining how audio devices such as equalizers, compressors, and A/D converters work internally, and how they're spec'd and tested, rather than merely describing how to use them. This book is also unique because it includes much original research, such as methods to test the audibility of distortion and other artifacts using your own listening system, while explaining why many common home-made tests are not valid. It also addresses the perennial "measuring versus listening" and "subjectivist versus objectivist" debates head on, and resolves them using science, logic, and hard proof. There's plenty of myth-busting and consumerism too. Indeed, truly understanding how audio gear works leads to smarter buying. So while I won't tell readers what brand power amplifier to buy, I explain in great detail what defines a good amplifier, so people can choose a first-rate model wisely without over-paying.

Most explanations throughout the book are platform-agnostic, applying equally to Windows and Mac computers, and to most software and hardware. Many audio and video examples are included to better present complex topics such as vibration and resonance. Other videos demonstrate editing techniques and audio processing, and there are several video interviews with skilled musicians demonstrating their instruments and playing techniques. In the piano video, a professional piano technician disassembles a $100,000 Steinway grand to show how it works! Of course, there's also a comprehensive Acoustics section, bringing together much of my writings from past years into one coherent reference, along with a wealth of new information. There's literally nothing else like this book.

The Audio Expert is due out April 15, 2012, with an anticipated length of 656 pages and a list price of $54.95. The book can be pre-ordered now at the Amazon book store, and will also be available as an eBook at the Kindle store. Watch for a glowing review in an upcoming issue of Electronic Musician magazine.



Upon looking at the chapters it's clearly for those in the making music business, sound engineering, so I asked could a reduced pdf online version be avaialble....
http://forums.musicplayer.com/ubbthreads.php/topics/2383341/Re_Ethan_s_book#Post2383341
Ethan;
I'm a Home Theatre enthuasist.
Looking over your book table of contents, http://www.ethanwiner.com/book_toc.htm clearly it is written for those who are in the "music business".
Making, creating, recording, editing, playback, etc.

For the Home Theatre related portions, is there any thinking to make say a smaller version, even download pdf only.
Ch 1, 2, 3, 4, 16, 17, 18, 19, 20, 22, 23, maybe some others.
Just a thought....

btw, Low hanging fruit is very clear, it's been stated here and many-many other acoustic forums:

1) Pick RFZ zone as your small room acoustic model, it's the easiset for DIY (IMO); front sound stage specific ; I've not seen surrounds addressed specifically in the various small room acoustic model's ....
2) Broadband bass traps in corners, big ones if possible, 34" x 24" x 24" (use pink fluffy for that size). Soffit style on wall/ceiling is also.
Plan to cover them on room facing surface with thick kraft paper or 6mil plastic to reflect the mid-hi freq back into the room. Fabric cover over that.
3) Using mirror trick, plan where your side wall 1st reflection treatments could be
.....If you want to use measurement and verify exact placement, use ETC and the techniques discussed for ID/placement.
.....If not, using just mirror trick, you may over dampen slightly, or may not get all the reflection points, but definitley improvement will be heard (the 90/10 rule)
4) by the book for side wall treatments, 4" OC703 + 4" air gap is best to even absorption thru the freq spectrum 250hz and up, again 16" of space may not work for some, 2" + 2" air gap will leave some of the lower freq not addressed.
>>Trade off time for the customer to decide
5) Using mirror trick, plan where your ceiling 1st reflection treatments could be....same comments as 4) above.

Plan them
Build them
Hang them
Listen and enjoy them :D

Better is measurements, but many don't want to shell the $225 or so for measurement mic/gear and learn the software.
Not hard, but just one more thing in a busy life.

I see some are asking for a "Plan...do...check....act" cookbook approach.....

https://encrypted-tbn0.google.com/images?q=tbn:ANd9GcSGja13qAFMz6khnt6LeVLTlfkM3b0CsUUMhxxry0t z_b_yU5ky

Looking at this link, everyone can see visually the various small room models, it's 7 pages from the book "Acoustics and Psychoacoustics Applied"
http://eetimes.com/design/audio-design/4015907/Acoustics-and-Psychoacoustics-Applied--Part-1-Listening-room-design?pageNumber=0

btw, Low hanging fruit is very clear, it's been stated here and many-many other acoustic forums...

Seems reasonable and that it'd do the most good with the least harm.

btw, Low hanging fruit is very clear, it's been stated here and many-many other acoustic forums:

2) Broadband bass traps in corners, big ones if possible, 34" x 24" x 24" (use pink fluffy for that size). Soffit style on wall/ceiling is also. Plan to cover them on room facing surface with thick kraft paper or 6mil plastic to reflect the mid-hi freq back into the room.


Is there any cons if chunk bass traps are covered with 6mil plastic paper surrounding three sides of triangle? If it is not advised, how do you stop fibers coming from the back or sides?

Is there any cons if chunk bass traps are covered with 6mil plastic paper surrounding three sides of triangle? If it is not advised, how do you stop fibers coming from the back or sides?

Sorry not stated, they need fabric covers over the reflective material for that reason.
Plus, they need to look nice, right? :)

I think he's asking about totally encasing the SSC's in poly/kraft paper for environmental reasons.

Jeff

I think he's asking about totally encasing the SSC's in poly/kraft paper for environmental reasons.

Jeff

Yes. that is right. I wonder encasing triangle basstrap in 6 mil plastic instead of just front side is ok or causes any problems.

I intend to encase first with 6mil plastic then with fidelio velvet cloth.

Yes. that is right. I wonder encasing triangle basstrap in 6 mil plastic instead of just front side is ok or causes any problems.

I intend to encase first with 6mil plastic then with fidelio velvet cloth.

As I type this on my iPhone, in my basement home theatre, watching pirates of the carribean with my 6 yr old son, I'm looking at 6 bundles of pink fluffy sitting wrapped in their plastic still.....there for some side experiments on low freq bass stuff....need I say more.

Many people buy and stack pink fluffy in the corners. Sure, it's compressed, but gives you directionally the improvement possible. Uncompress it for the install.
Fully wrapping in plastic is up to you.

I believe dragon or local posted some link to clear the issue of health of loose fibers, simply a non issue.

Have fun.

Yes. that is right. I wonder encasing triangle basstrap in 6 mil plastic instead of just front side is ok or causes any problems.

I intend to encase first with 6mil plastic then with fidelio velvet cloth.

+1 on what Mike said, plus, if the traps are behind a false wall, it's just silly to spend the cash on Fidelio. Go to Joanns and buy some some cheap speaker cloth to cover. Save the Fidelio for the screen frame, although I personally think that's overkill as well compared to some less expensive options.

+1 on what Mike said, plus, if the traps are behind a false wall, it's just silly to spend the cash on Fidelio. Go to Joanns and buy some some cheap speaker cloth to cover. Save the Fidelio for the screen frame, although I personally think that's overkill as well compared to some less expensive options.

Thanks. I already bought 20 yards of Fidelio and it is sitting for a while. After buying, I got confused if it is accoustically transparent enough for sound absorption and did not do anything with it. At the time of purchase, my intention was to make screen wall and surroundings as dark as possible and never thought about filling space with bass traps or first reflection panels.

Nathan, we can help you. But help us by posting the REW .mdat file so that we can convolve the frequency response into the various views and window them accordingly.

And as local observed, we want to drive each source individually with the measurement mic remaining in the EXACT same (reproducible) position for all current and future tests.

And with treatment in place, its difficult to say what can be done, or what original actual issues exist that require treatment and thus to suggest what needs to be done, as we do not have the untreated baseline response to judge. Untreated measurements would be a wonderful addition if the concept does not scare you too badly... We can then determine the effectiveness of the treatments and suggest any additional measures...

And seeing as how REW can be used in any number of configured audio topologies it hardly seems work all the effort to attempt to configure it to a specific configuration when it is simply but one possible topology out of many when its easier and quicker to simply manually change the input relative to the device you want to test.

Okay, once I get the measuring of individual speakers working, I'll post the mdat file. I assume the one for the stereo pair isn't as useful, interesting?Okay, once I get the measuring of individual speakers working, I'll post the mdat file. I assume the one for the stereo pair isn't as useful, interesting?


Working on getting set up to test speakers individually. First step was just to remove bass mgmt, the sub, etc and do a fresh measurement of the room with all channels driven with the test sweep.

Calibrated mic from Dayton. I'll post the mdat file and this picture set of pictures.

EDIT: mdat file is 1.7mb and the upload limit is .5MB

Single speaker measurements. Right front, run full range, no sub, no eq, etc.

nathan_h, it is best to post the files (upload to www.sendspace.com).

also, ETC needs to utilize loopback --- in preferences/analysis, DE-select 'T=0', Select 'use loopback for timing reference', and DE-select 'decimate IR'

re-run the test and post .mdat files (one speaker/source at a time).

I'll re-run ETC, but for now, here is the mdat for the single speaker test.

http://www.sendspace.com/file/n56o2r

I am looking for some advice and may have some dumb questions, but would really appreciate the help.

I ran across a really good deal on (4) Thiel PowerPlane 1.2 speakers. I already have the speakers for a surround sound setup in a HT without using these speakers for that. I am in the process of building a garage building with a finished space above. In the garage area, I am planning to install a projector and am thinking about installing the four Thiel speakers in this room (the room is 30' x 40' with 12' ceiling). I will use this primarily to watch sports when people are over and listen to music. Upstairs, I plan to setup more of a theater with surround sound. I would like to hook everything up through one receiver and I am looking at the Yamaha Aventage RX-2000. Will I be able to send video to my theater room TV and the projector as well as power all of the speakers with this one unit? Do I need an amp for the Thiel speakers or will this receiver work without an amp?

Again, any advice is appreciated as I am trying to learn as I go and make sure I make the right decisions as I am in the build process on the new building right now.

This is the acoustical treatments thread ...

yeah, i recommended he ask here, since i've seen a few discussions of the calculations regarding speaker sensitivity, spl, and amp output. there might be a better place to ask but i couldn't think of one...

yeah, i recommended he ask here, since i've seen a few discussions of the calculations regarding speaker sensitivity, spl, and amp output. there might be a better place to ask but i couldn't think of one...

Probably be more likely to get good advice on a Thiel thread or one for the receiver. Members on a Thiel thread would be familiar with the speakers.

Jeff

reasonable suggestion.... ironic that *that* is where he posted at first.... crickets.

Maybe they are all off enjoying their speakers. :)

bingo

reasonable suggestion.... ironic that *that* is where he posted at first.... crickets.

Maybe this was the wrong thread but the right forum, if it has to be one question.

Or it could be two questions: one in Thiel and one in receivers.

Opinions on two different diffusers sought:

I have been using broad band absorption, the basic GIK panels, on my side wall first reflection points.

Recently, I got a good deal on some cheap Auralex Metrofuser panels. They are shallow and made of styrofoam, but I figured it would be an interesting experiment to place them over the side wall panels and see what I thought.

The result? Bigger soundstage and all spatial cues appear to be preserved.

So now I'm sold on the idea of diffusion at my side wall fist reflection points.

But these panels may not be ideal. I'm still trying to learn, but so far what I have picked up is:

The pattern should not repeat,though being mirrored is okay. In that case, since the panels are 24" square and I only have to cover 4' square, they should be okay.

The depth should be shallow, when seated lose to the panels. I'm about six to seven feet from the side wall reflection points, so I think that's considered close. These panels are only two inches deep, so the wells are even shallower, so I think that's good.

But they are made of styrofoam, which can't be spray painted and would probably still have low WAF even when painted. And I cannot tell what calculations were used for them.

So I am considering two upgrades:

http://www.decware.com/p1324.htm look good, and buying as a kit makes them affordable. The narrowness of the wells seems to mean their diffusion only happens at higher frequencies.

The other option is the QRD panels from GIK. They are bother wider (which I think is good in that it means a wider range of frequencies are impacted) but they are also deeper, which I suspect is not ideal in the close quarters I'll be using them in.

Thoughts?

How about a third option: BAD panels for way higher WAF?

They diffuse and absorb the LF.

EDIT: I didn't phrase that well above. For the record, it looks like they diffuse upper and mid frequencies and absorb lower than their diffusion threshold, such as 1000hz, depending on the particular model's design.

How about a third option: BAD panels for way higher WAF?

They diffuse and absorb the LF.

Those look interesting, but I don't think I'd get 32 square feet of coverage for 600 bucks, like the other two solutions. She's okay with the look of these others. It's just the styrofoam panels that have to go :-)

Nathan...

Lots of issues using those panels.

First, their effective bandpass is FAR too high. To be effective over the broadband bandpass, you are going to need QRD style diffusors generally about a foot deep to get the lower extension required.

With the Auralex product you are effectively EQing the reflected energy seriously coloring the direct sound. The minority of he mid and low mid energy does not even see them and effectively see a flat wall surface.

If you'd like a more complete explanation and additional practical options, PM me and we can talk by YM, Skype or telephone...

Having been reading this thread for a few years, I think a conversation about diffusion here may be useful (I don't recall seeing lots of details). Thanks for the offer to take it off line. But if we can keep it online, I suspect others may find it interesting/useful.

My understanding so far is that to get impact over a broad frequency range, I need a panel with WIDE wells, and to get a panel that is impactful at short distances, I need a panel with SHALLOW wells.

So I agree the Auralex aren't the right ones. And the DIY kit I list doesn't have wide enough wells. I was actually thinking the GIK panels might be too deep.

But you are suggesting the GIK panels aren't deep enough, correct? (I've mentioned three different commercial solutions in my post, so when you say "those panels" I'm not sure if you mean all three, of just the Auralex ones.)

read over this a few times - http://www.subwoofer-builder.com/qrd.htm
collo did an excellent job with the tech guide and perfectly suitable for the novice.

read over this a few times - http://www.subwoofer-builder.com/qrd.htm
collo did an excellent job with the tech guide and perfectly suitable for the novice.
Thanks. Bookmarked.

dont bookmark it - read it.

and here's the original discovery thread if anyone is interested:
http://www.gearslutz.com/board/bass-traps-acoustic-panels-foam-etc/407250-2-ch-listening-room-aiming-best-possible.html

read over this a few times - http://www.subwoofer-builder.com/qrd.htm
collo did an excellent job with the tech guide and perfectly suitable for the novice.

Yep, that's the only coherent overview that I have found without a lot of marketing hype related to one brand.

What I conclude from it:

1. The auralex panels are shallow enough for near field use but lack with width of individual wells that would have impact on midrange frequencies and don't have fins which impacts performance.

2. The GIK panels (QRD) have the width of wells that would get down into the midrange, but are deeper than ideal for near field use (but maybe my seven foot distance is okay). But again no fins.

3. The DIY kits are great for near field, but also suffer from narrow widths meaning they don't get into the midrange.

Conclusion: The GIK is the least compromised of the choices for my application.

what on earth do you mean by "brand"??? we're talking number theory here..

and fyi there is a reason why this book is constantly recommended:
http://www.amazon.com/Acoustic-Absorbers-Diffusers-Theory-Application/dp/0415471745/

i suggest you investigate your local library.

me personally, i dont see any reason to utilize any QRD or PRD under N23.

what on earth do you mean by "brand"??? we're talking number theory here..


Every manufacturer seems to have their secret sauce, like RPG and RealTraps using absorption / diffusion combination products, or Auralex no longer publishing specs and test results, though they did at one time, and imply there is science behind their offerings.

and fyi there is a reason why this book is constantly recommended:
http://www.amazon.com/Acoustic-Absorbers-Diffusers-Theory-Application/dp/0415471745/

i suggest you investigate your local library.

me personally, i dont see any reason to utilize any QRD or PRD under N23.

I am finding that the statements about controlling modal energy through traps and specular energy through diffusion are also matching my listening impressions (or vice versa) so I am on the hunt for affordable diffusion.

I haven't read the book, just the web site, so I am not sure I understand why an N7 QRD panel is less desirable than absorption at a side wall first reflection point.

Sorry, but you are jumping to conclusions on the basis of marketing brochures rather than a familiarity of the concept based on mathematical sequences behind how they work!

As local has observed, of only folks would first avail themselves of just a few definitive texts rather than the myriad hours and number of marketing pamphlets folks with which seem to be intimate! And then we get to listen to the excuses as to why the sources are not read...

Secret sauce? What? They optimize them or they don't. Or in too many cases, in the name of ease of manufacturing they cut corners and spun that as a unique feature. The basis for the design was developed by Dr. Manfred Schroeder. Hence why this style of diffusor is commonly referred to as a "Schroeder diffusor". There is no secret. Well, except to folks who spend more time reading marketing brochures than actual explanations of the principles!:D

And all of the combinations are rather easily understood. There is no secret! Simply an understanding of the basics that allow folks, in conjunction with an understanding of what is happening in a bounded space, and an awareness of how such behavior would befit from being modified, to put the behavior in the room together with the behavior of the various treatment device/material characteristics so as to appropriately address the full spectrum which needs to be addressed.

Modes can be controlled with diffusion, but as one would quickly learn in the introduction of AA&D, this is not commonly done as the size of the diffusors is prohibitively large. If you want an idea of just how large, look at the PRD diffusors used in Blackbird above and note that they barely get down to ~110 Hz - and that is at the expense of losing ~7 feet of space to the diffusors.

You would also quickly learn that the issue with size and spacing away from boundaries for velocity based porous absorbers is a fundamental limitation for them as well - with the optimal tool for such modal issues being pressure based tuned resonant absorbers - which are a bit more complex to design and to iteratively install and tune.

And a single n7 QRD is not going to do much for you. As also basic to their function is the issue of periodicity and the advantage of an increase in the complexity of the dispersion of he various reflected wavelets and their increased interaction (superposition). Basically you have a choice of going with fewer complex high n units, or a larger series of low n units incorporating an inverse unit inserted per the Barker modulation sequence. But seldom will one low n unit be used alone. They also have spacing requirements, as since diffusers typically used in rooms have a lower frequency limit of around 300-500 Hz, a minimum distance of 3 yards/meters is ideally recommended, but this is often compromised with the result being hat the lower octave is characterized by more scattering than diffusion..

Again, ALL of this basic information about their function and design is rather elegantly addressed in the 2-3 page tutorial on the QRDude webpage, or in yet more detail, including applications, in AA&D.

This stuff isn't that difficult. So again, and pardon me for harping on it, but PLEASE (anyone who has questions) at least do a BIT of actual research into this stuff. And then we can spend more time addressing real concerns rather than debating marketing claims that should be rather easily addressed by an informed user/consumer of such tools.

I read the QRDude web page, and shared my conclusions based on what I understood from those pages.



What I conclude from it:

1. The auralex panels are shallow enough for near field use but lack with width of individual wells that would have impact on midrange frequencies and don't have fins which impacts performance.

2. The GIK panels (QRD) have the width of wells that would get down into the midrange, but are deeper than ideal for near field use (but maybe my seven foot distance is okay). But again no fins.

3. The DIY kits are great for near field, but also suffer from narrow widths meaning they don't get into the midrange.

Conclusion: The GIK is the least compromised of the choices for my application.

If I am misunderstanding the concepts, it's not due to lack of trying.

As best I can tell, dual, mirrored QRD diffusers on each wall at the first reflection points is going to be my best option under $1k.

If there is something better for that four feet wide, seven feet tall section of side wall treatment, I am eager to learn.

I would suggest a few initial considerations.

... I would suggest that you first focus on ascertaining what is actually happening over the full time spectra of the room response, and then develop a comprehensive strategy rather than simply focusing on one treatment out of context with the whole ...
Thank you!

I've done some measuring with REW, posted above, but this was with GIK absorption panels in place on the side walls. I think the next step is to do those measurements with bare walls.

I've done some measuring with REW, posted above, but this was with GIK absorption panels in place on the side walls. I think the next step is to do those measurements with bare walls.

Hey Nathan,
I would recommend sending us your measurements through email also. There is no reason to go around and around with stuff like this.

The fact is, with real measurements much is possible, and the only "reason to go around and around with stuff like this" is that we do NOT have functional measurements nor an established response goal nor even adequate information about the space in which they are to be installed

I asked him to send measurements so we could see if it is a good fit.

I am not sure if you aimed your other part of your post at my company or not but we have been selling diffusion for 5 of the 7 years of being in business. And we are getting ready to put a new line of tuned bass traps on the market. Care to beat me up on that? :eek::D:D

The room is 17' x 12' x 7.6'. So placing a panel (or any type) along the side wall first reflection points means it's about 7' from the MLP.

I have measurements from the MLP, with one channel driven and with all channels driven.

Here is the measurement for one channel, in the current room, full range without the sub: http://www.sendspace.com/file/n56o2r

(Which are better? Should I re-run the measurements without any treatment in place at the side wall reflection points?)

For standards, I need some guidance. Which of the following or some other standard is best to strive for? I am optimizing just for the front row.

IEC 60268-13?
ITU-R BS 1116-1? or the variant EBU 3276?

Summary of the standards, attached, and some photos of the room.

It may be hard to see from the photos, but I have:

1) two GIK 242 panels on each side wall first reflection point area, for a total coverage of 4' x 4'.
2) a bass trap 2 feet tall, 6 inches thick, running the full length of the front wall, at the floor/wall intersection, simple OC700 series, set off the front wall by 2 inches.
3) There is an additional GIK 244 panel on each side walls, right at the screen wall -- ie, not at a reflection point, but essentially in the corner, for bass trapping
4) and two GIK244 traps on the back wall, more or less centered above the back row chair backs.

But being a tinkerer, I picked up some cheap diffusion panels (metrofusers) from Auralex, little 2inch think stryrofoam panels, and placed them over the absorbers at the side wall first reflection points -- and liked the change. But I know those panels are not ideal -- little depth, ugly, and no stated specs or science behind them.

My general notion, pending education, is to replace #1 with diffusion (and re-purpose the 242 panels into corners for bass trapping).

But it is nice to see the all too common nonsensical "you can't have too much absorption" phrase slowly begin to wax in popularity on these forums. Including by representatives of some of the same firms to which you mention. And that has only been occurring in only the last 2-3 years!

Upper frequency absorption? sure. Bass trapping? Most small rooms need as much as they can get. As a company we have always offered custom builds of just about anything, but most people do not have the budget which is where broad band fits the bill a lot of times.
How is your room treated? Pictures you can share? Testing you can post?

The room is 17' x 12' x 7.6'. So placing a panel (or any type) along the side wall first reflection points means it's about 7' from the MLP.

I have measurements from the MLP, with one channel driven and with all channels driven.

Here is the measurement for one channel, in the current room, full range without the sub: http://www.sendspace.com/file/n56o2r

(Which are better? Should I re-run the measurements without any treatment in place at the side wall reflection points?)

For standards, I need some guidance. Which of the following or some other standard is best to strive for? I am optimizing just for the front row.

IEC 60268-13?
ITU-R BS 1116-1? or the variant EBU 3276?

Can you just zip the file and post it here?

Hey Nathan,
I would recommend sending us your measurements through email also. There is no reason to go around and around with stuff like this.

Thanks. In addition to the link to the measurements, I have sent a note to you and Bryan.

Can't upload to AVS, since a zipped mdat file from REW is above the AVS max size for attachments.

Okay, I'll re run the test. I didn't have loop back set up, so all the absolute timing measurements are wrong -- though the relative times are valid.

And please generate the sweep with NO smoothing - as that extra information is actually useful.

That said, you have a substantial high gain very early arriving reflection that will be VERY audible.

That said, here are a few quick observations...
You have quite a few sparse (isolated) specular arrivals that would benefit from being resolved to their point of boundary incidence

The early arrivals, as high in gain as they are need absorption, as diffusion will not address them to the degree necessary to mitigate associated problems.

The other lower gain early reflections can benefit from diffusion (or absorption depending upon the logistics and whether diffusion may aggravate other concurrent behavior).

The later arriving specular arrivals are dominated by many sparse reflections that are of much higher gain than the other proximal reflections. These interfere with proper localization.

To the degree that these later arriving sparse reflections are primarily from the sides of the room would be to your benefit.

These would greatly benefit from diffusion that would reduce the gain of the individual sparse focused reflection while spreading the energy out spatially and temporally - and optimally form a lateral orientation - thus increasing the density of the reflected energy soundfield, effectively 'filling in' the gaps and rendering the gain structure more uniform as it decays.

http://i277.photobucket.com/albums/kk78/eatmycabbage/th_ETC70.png (http://i277.photobucket.com/albums/kk78/eatmycabbage/ETC70.png)

Nice post! I think this is the first time I've come across an actual analysis of the ETC with commentary on treatment relating to the measured data. Thanks. :)

Run again, using the loopback calibration.

http://www.sendspace.com/file/3nwjaq

direct signal still arriving at T=0

http://i.imgur.com/BKd2Q.jpg

AC/electrical device causing interference?

60 cycle
A classic example.

First try running your computer rig off battery only and see if that makes a difference.