Its thickness. Look up "Bonded Logic Inc's UltraTouch Cotton" r-13 on Bob Gold's absorption site (http://www.bobgolds.com/AbsorptionCoefficients.htm). The 3.5" thick stuff is very effective (95% down to 125 Hz), but it's 3.5" thick!

I thought about coming up some crazy 2' wide cutter to slice the 3.5" stuff into 1.75" halves and use that (slightly compressed) in a 1.5" frame, but it didn't seem worth the effort.

Interestingly, the stuff I have has a certain amount of plastic fibers (polyester? nylon?). If you compress it and heat it, the fibers melt and it retains it's new thickness/density. I thought about trying to 'densify' my cotton a bit and make it thinner. Again, I couldn't think of a practical way to do it. The acoustical properties of what I had in the end would be unknown anyway.

Its thickness. Look up "Bonded Logic Inc's UltraTouch Cotton" r-13 on Bob Gold's absorption site (http://www.bobgolds.com/AbsorptionCoefficients.htm). The 3.5" thick stuff is very effective (95% down to 125 Hz), but it's 3.5" thick!

Compare with AcoustiCotton, right above it on Bob's page. Or Echo Eliminator bonded acoustical cotton, right below it.

Regards,
Terry

pmeyer, thanks that is an interesting alternative. I have corner bass traps to fill also and I might use that instead of the more rigid Rockwool 60.

Heck its cheaper and better if you compare 3.5" vs the Rockwool 60 2".. I already spend $150 on the rockwool. I could have spend $160 (edited, shipping is $60) on this stuff and it has better numbers :(

I wonder why its never talked about before, I guess I just missed it.

You need to be careful comparing. It looks to me like 4" rockwool has about the same numbers as the 3.5" cotton. I'm betting 2 layers of 2" rockwool are the same as or better than 1 layer of 3.5" cotton.

It comes down to what you can get, what is cheap, and what is easy to work with.

You need to be careful comparing. It looks to me like 4" rockwool has about the same numbers as the 3.5" cotton. I'm betting 2 layers of 2" rockwool are the same as or better than 1 layer of 3.5" cotton.

It comes down to what you can get, what is cheap, and what is easy to work with.

Well to get the same sqft..I think its about the same cost for 2" vs 3.5" so that alone shows me that the UltraTouch stuff is the better buy, much better coeffecient at low frequencies.

R-13 3.5" (mm) A 0.95 1.30 1.19 1.08 1.02 1.00 1.15

vs

RXL 60 2" 0.32 0.81 1.06 1.02 0.99 1.04 0.95


I was using the Rockwool60 in the corner traps, which will have a frame just like yours. I had to cut the 2x4 rigid sheets to fill the frame. Now I can easily fill the frame with long lengths of the ultratouch, compressing it together is I add more layers. I just seems so much easier in my books.

I just purchased 106 sq ft of the stuff....I will fill one corner trap with it and another one with the Rockwool 60 I own.

Some lucky member will probably get a great deal from me, I think I have too much OC703 and too much Rockwool 60...but we shall see.

Actually, the 2" with a facing is relatively good down reasonably low.

Coefficients:

0.63 0.56 0.95 0.79 0.60 0.35

There's a bit of a hump in the middle but it's still respectable down at 125Hz and lower. Just helps in the length dimension with midbass boominess and giving some broadband control opposite the screen area without killing the highs on the back wall in the surround field.

Bryan

Some lucky member will probably get a great deal from me, I think I have too much OC703 and too much Rockwool 60...but we shall see.
Hold onto it! Properly used and placed, this is a pile of gold. :)

Regards,
Terry

I just was using that reflection program from this forum and it shows a reflection on the ceiling.

I dont read much about ceiling treatments. Im thinking that after everything is done, I might build a 2x4 panel and place it on my ceiling at the reflection point.


Hold onto it! Properly used and placed, this is a pile of gold.

Yeah, its nice to have too much just in case. I also think my bass traps will be better now because I can go thicker with them.

I just was using that reflection program from this forum and it shows a reflection on the ceiling.

I dont read much about ceiling treatments. Im thinking that after everything is done, I might build a 2x4 panel and place it on my ceiling at the reflection point.

Ceiling reflections may or may not be a problem. If you happen to be using THX front speakers, then they will probably not be. This is because the required dispersion pattern for a THX main is wide horizontally, but narrow vertically.

Regards,
Terry

if GOM is too expensive a fabric for me, but I don't want the farm smell of some burlap, what would be a good mid-end fabric that passes the blow test and comes in a variety of colors?

I went to JoAnn's, but it would've taken me hours to blow through every damn fabric. Plus I'd look like a complete moron blowing on every fabric! :)

Ceiling reflections may or may not be a problem. If you happen to be using THX front speakers, then they will probably not be. This is because the required dispersion pattern for a THX main is wide horizontally, but narrow vertically.

Regards,
Terry
That is a very good point. THX-certified speakers have very tightly controlled vertical dispersion just for this very reason - reduce/eliminate ceiling (and floor) reflections. Having said that, and in line with my "I think I did too much" feeling, I did place a front ceiling absorber, which I am now considering removing (and possibly replacing with diffusion). I have THX Ultra speakers.

Pics here (http://peparsplace.com/html/19.html).

if GOM is too expensive a fabric for me, but I don't want the farm smell of some burlap, what would be a good mid-end fabric that passes the blow test and comes in a variety of colors?

I went to JoAnn's, but it would've taken me hours to blow through every damn fabric. Plus I'd look like a complete moron blowing on every fabric! :)

Muslin will work well for treatment covering and is very inexpensive. It is not, however, suitable for in front of speakers. It's also not a fire rated material.

Bryan

Muslin will work well for treatment covering and is very inexpensive. It is not, however, suitable for in front of speakers. It's also not a fire rated material.

Bryan

Thank you. It won't be in front of speakers.

BTW, appropriate that you replied, I have a order on its way from GIK as I type this. Tri-corners and some 442's. I'm finally getting around to treating my extremely small room. Of course I do it now after I spent the last few days tuning my system as best I can. When I get the treatments in, I'm sure I'll have to re-tune.

As for treating rear wall reflections from front speakers, this is often not necessary. Unless you are very near the rear wall, the reflection will not occur within the first 15 milliseconds or so of the direct sound. This means that your brain cannot merge the two sounds into a single sound with degraded spatial localization.

Also, unless you are very near the wall, any significant notch filtering due to interference between direct and reflected sound will be very low in frequency -- low enough to be absent because it has been offloaded to your subwoofer by your bass management system!

Regards,
Terry

Have now completed acoustic treatment prototyping.

I had a real problem with bass modes in my screen 'alcove' in the front of the room so I choose to treat the entire alcove with 4" mineral wool (covered with 1" linacoustic - cheaper than GOM)

2'x6'x4" bass traps in the rear corners; and

48" high panels of 1" linacoustic on the side walls (just cut pieces of linacoustic - have not framed them yet)

See before and after RT60 and Freq response below (note before is red, after blue)

http://idisk.mac.com/dbbarron1-Public/Theater/apr24 rt60.jpg

http://idisk.mac.com/dbbarron1-Public/Theater/apr24 treatments.jpg

Please note that I have 4 subs in 1/3 2/3 positions on the front and rear walls.

Have to say the RT60 may be a bit low. I may scale back the side panels a bit.

However, the room sounds very good, albeit a bit dead. Whenever I listen in a room like this I like to say that it ruins all my recordings. I hear every error in mix, artificial reverb, MP3 (my library is in iTunes) encoding compression, etc. But when a recording is good, its great!

All comments welcome!

Here is some more data from the prior post. Impulse and waterfall

http://idisk.mac.com/dbbarron1-Public/Theater/waterfall.jpg

http://idisk.mac.com/dbbarron1-Public/Theater/impulse.jpg

On the impulse response, I have identified the first 3 large impulses as the following:

3ms - ceiling first reflection. When I temporarily placed a piece of linacoustic at this reflection point the peak decreased 10db - strategy - will treat

6-8ms - reflections from along the length of the soffit vertical portions - this section is only 8" high but is clearly causing substantial reflections - when I placed a temporary piece of linacoustic here, the reflections decreased 8db - strategy - will treat

9-10ms - side walls, already treated with 1" linacoustic -might be column edges also - likely leave be. Perhaps add another layer?

General questions

How is the performance of this room?

Once treated, are the first reflections sufficiently mitigated (per above)?

Is the RT60 too low (see prior post)?

Regards
db

db,

The only reflection that really needs treatment is the ceiling reflection at 3 ms. The other reflections are low enough not need treatment.

What are the dimensions of this room?

Regards,
Terry

Thanks Terry - Here is a rough sketch (dimensioned)

http://idisk.mac.com/dbbarron1-Public/Theater/predicted modes.jpg

Hey db,

What equipment are you using to generate your measurements and graphs?

That's great news from Terry about only needing to treat your ceiling, eh?!

Have you got any pics of your room--I'd love to see your quad subs!

Keep up the great work,
Phil

Hi db,

I'd say that your reverberations times in the octave bands 125 Hz and 250 Hz are a bit too high relative to the higher frequency octave bands. These higher frequency octave band reverberation times are not too low on an absolute scale, but too low on a scale relative to the 125 Hz and 250 Hz octave bands. This unevenness can make the room sound too dead. As for the 63 Hz octave band, reverberation time measurement at these low frequencies is too unreliable in small rooms to be useful.

But since your upper frequencies are fine, you just need more absorption at the highly treatable 125 Hz and 250 Hz octave bands. I recommend either DIY bass traps, as described in this forum and on http://forum.studiotips.com/viewtopic.php?t=535, or ready-made bass traps by forum members RealTraps or GIK Acoustics.

Regards,
Terry

As for treating rear wall reflections from front speakers, this is often not necessary. Unless you are very near the rear wall, the reflection will not occur within the first 15 milliseconds or so of the direct sound. This means that your brain cannot merge the two sounds into a single sound with degraded spatial localization.

Also, unless you are very near the wall, any significant notch filtering due to interference between direct and reflected sound will be very low in frequency -- low enough to be absent because it has been offloaded to your subwoofer by your bass management system!

Regards,
Terry

Terry--how close is close to the back wall? My setting is about 2ft. off the back wall.

My room is on the wide orientation (27'w x 15'd x 8'h)...

Thanks for the insight.
Phil

Terry--how close is close to the back wall? My setting is about 2ft. off the back wall.

I'm not Terry but I'll do my best. :D

Having a reflecting wall close behind you is a problem for two reasons. First, if the wall is less than ten feet away, reflections are considered "early" and harm imaging and clarity at mid and high frequencies. Second, the closer you are to a reflecting wall, the worse the peaks and nulls will be.

My room is on the wide orientation (27'w x 15'd x 8'h)

This is why it's better to have the speakers fire the longer way down the room - it puts the wall behind you that much farther away. These two short articles explain in more detail, and prove the points with response graphs:

http://www.realtraps.com/art_room-setup.htm
http://www.realtraps.com/rfz.htm

--Ethan

Terry - I see your point from the waterfall regarding the 125 and 250Hz bands.

I'll try experimenting with the existing bass traps positioning and supplementing same.

Since my sidewalls have 1" linacoustic panels, and the 1" absorbtion parallels the issues you identify (absorbtion falls off starting at 250hz), would increasing the sidewall panels to 2" (double 1" - I have the extra material) address the issue? higher frequencies should be unaffected as the panel absorbtion is already near 100% in the upper bands- same for RT60 above 250hz.

allred: See Mayflower Construction Thread for pics - using 4 OEM10s for subs. LCRs are WCW config (Dayton reference 10"+Seas Coax).

db

Terry - I see your point from the waterfall regarding the 125 and 250Hz bands.

I'll try experimenting with the existing bass traps positioning and supplementing same.

Since my sidewalls have 1" linacoustic panels, and the 1" absorbtion parallels the issues you identify (absorbtion falls off starting at 250hz), would increasing the sidewall panels to 2" (double 1" - I have the extra material) address the issue? higher frequencies should be unaffected as the panel absorbtion is already near 100% in the upper bands- same for RT60 above 250hz.

Yes, the 2" material will help. Also, using ASJ (All Service Jacket) or FRK (Foil Reinforced Kraft) faced fiberglass will dig deeper into the low frequencies and give your room a little less in the highs. An ideal place to do this is on the upper parts of your side wall, above the positions of early reflections. You may may also use your existing fiberglass to 2 inches with a covering of ordinary Kraft paper.

Regards,
Terry

I'm not Terry but I'll do my best. :D

What Ethan said. :D

- Terry

Terry--how close is close to the back wall? My setting is about 2ft. off the back wall.

My room is on the wide orientation (27'w x 15'd x 8'h)...

Thanks for the insight.
Phil


My room is very, very similar....25 W x 14 d x 8 h.....one row, 2 feet off the back wall!!!

Yes, going 25 deep would be the better option but its not going to happen so what can we do???

I have read enough to believe that if I have 2" across the back wall 24 to 48 inch high that I should be able to still control the reflections.

2 feet is too close to the back wall to get away without treatment. You'll need about 4 inches of unfaced semi-rigid fiberglass or equivalent. You can also use a 2" thickness, but leave a 2" air gap to the wall.

Regards,
Terry

2 feet is too close to the back wall to get away without treatment. You'll need about 4 inches of unfaced semi-rigid fiberglass or equivalent. You can also use a 2" thickness, but leave a 2" air gap to the wall.

Regards,
Terry

OK, so I have been planning on having 1" Linacoustic from the floor up to 38" high all along the back wall in a boxed panel (in fact, it will be around the entire perimeter of the room).

Should I increase the depth of the back wall boxed panel to accomodate some 3" mineral wool or spinglass that I have? Will that work?

I'm assuming that the 4" panel you are describing is meant to be mounted on the wall centered at ear height and most of the length wide.

In my case, WAF will not allow that ideal location of a panel for me, so I'm looking at options!

Big time thanks for the help!

Phil

2 feet is too close to the back wall to get away without treatment. You'll need about 4 inches of unfaced semi-rigid fiberglass or equivalent. You can also use a 2" thickness, but leave a 2" air gap to the wall.


wow, I didnt expect it too be that bad, thats going to be hard to do :( Maybe a 4" thick, 2x8 panel behind of the row is what I might be able to design. Frame it and mount it...it will look a little out of place but if it helps I could try it.


Is it because low frequences are bouncing off the wall too?

wow, I didnt expect it too be that bad, thats going to be hard to do :( Maybe a 4" thick, 2x8 panel behind of the row is what I might be able to design. Frame it and mount it...it will look a little out of place but if it helps I could try it.


Is it because low frequences are bouncing off the wall too?
Yes. At only a 2 foot distance, I'd expect you'd have a strong interfering reflection at about 141 Hz. This is because 141 Hz sound will be out of phase by 180 degrees after it travels a total distance of 4 feet. This is assuming incident angle reflection. So the reflection from mains will be a little farther, hence a bit lower in frequency.

This is likely to create a nice notch in your frequency response. :( This isn't the end of the world by any means, but if you have the opportunity to eliminate it from the start, it is a good idea. It will also fix strong early reflections which would be observed at higher frequencies. That's the reason I am recommending a wideband absorber (unfaced fiberglass), and not a membrane bass trap. And if this was your second row back, rather than your only seating row, I'd worry less about it because you'd still have a row of "prime" seats.

I'd also use a 4'x8' panel, since the wavelength is rather large and would therefore involve a larger area of wall for reflection.

Regards,
Terry

This isn't the end of the world by any means, but if you have the opportunity to eliminate it from the start, it is a good idea.

I will build the 4'x8' 4" thick panel, thanks!

I will build the 4'x8' 4" thick panel, thanks!

Just reading more about diffusors, would a 4x8 diffusor be an alternative?

Just reading more about diffusors, would a 4x8 diffusor be an alternative?

Diffusors are good on a rear wall, but not so good if you're only a few feet away from that wall. Moreover, most diffusors do little below about 1 KHz (depends on their depth), but peaks and nulls extend down to the bass range. See Terry's example of 2 feet giving a deep null at 141 Hz. There's also a peak at 282 Hz, another deep null at 424 Hz, and so forth. These low frequency peaks and nulls are not avoided with typical diffusors.

This page explains a frequency / distance calculator program you can download for free:

http://www.realtraps.com/sbirlbir.htm

--Ethan

Below 500Hz wall reflections are already diffuse - most "bass diffusers" on the market are in fact treble diffusers that provide bass absorption...because a real bass diffuser capable of disrupting modal and SBIR behavior is too huge to ship especially when it is best built into the room. The problem is the bass reflection even though spatially diffuse (spread to all angles but reduced in level) - still causes the frequency notches because it is not time diffused - but since you likely need bass absorption there are simpler ways to solve the problem.

I'l leave the shameless plugs for the experts in that dept....but a treble diffuser with bass absorption will do good for backwall reflections - but so will a broadband absorber (thicker fiberglass/rockwool panel).

You need to know if you have enough treble absorption already and if that spot is better to be treble diffused (with bass absorb) or treble absorbed (broadband bass trap) or treble reflected (bass only panel/membrane trap).

I am setting up my theater room using the following:

Pioneer Kuro 60 inch plasma 150fd
B&W 804s for fronts
HTM3S center
Ds8 dipolar rears
Sunfire Signature EQ sub
ND preamp and amp


I want to get the best sound possible. I will sit 10' from the monitor so that i am equal with the distance from my fronts from one another. I am trying to create as close to an equalateral triangle as possible.

!) QUESTION- That will put my fronts around 1' from the side walls. Is that enough? They will be around 2 1//2' from front wall.

2) Because I am only sitting 10' from monitor I will be 13' ft from my back wall. That seems pretty far away from the rear wall.

a) Is that an acoustic issue? Does it help or hurt being so far away?
b) What kind of acoustic treatment should I use on the back wall- absorbant shields or dissonance or none?

3) I want to do a good job with acoustic shielding.

a) I am thinking a shield on the front wall behind each front speaker (excluding center).
b) First reflection points on side wall using mirror trick.

1) Should i do ceiling first reflection point (flat drywall)?
2) I have carpet on the floor.

c) What thickness should I use on the absorbant shields 1" or 2"?

d) How important are bass traps and where should I put them in the top 4 corners or just the middle of the four corners?


THANKS FOR THE ADVICE!!!!!!!!!!!!!!!!!!

Dang--unlike penngray, I can't do a hanging panel just behind my seating on the rear wall. :(

So, considering my same wide-room/close-to-the-back-wall problem, WAF will let me have a built-in boxed-panel trim with GOM-covered 1" Linacoustic either from floor up to 38" or from ceiling down to 38". Above or below that I'm stuck with plain painted walls.

Which should I do?

Is is better to have the absorption above the ear-level all around, or below the ear-level all around? :confused:

I get one or the other, and WAF will not allow for individualized panels on the walls.

BTW, for bass-trapping I will have columns flanking my screen that I'll fill from the top of the L/R speakers to the ceiling with rockwool chunks, and I will have two columns on the back wall also filled with chunked rockwool.

So, which should I do? Whole-room treatment above or below 38"?

Any help completely appreciated!!! :)

Thanks,
Phil

So, considering my same wide-room/close-to-the-back-wall problem, WAF will let me have a built-in boxed-panel trim with GOM-covered 1" Linacoustic either from floor up to 38" or from ceiling down to 38". Above or below that I'm stuck with plain painted walls.

Which should I do?


You can not make the bottom half of your back wall 4" thick? place a shelf (maybe 6" deep) on it to blend it better with the top half. I would look just like a wall then?

Question(s) for the acoustic experts that are lurking...

The sketch below is the layout of my theater area. As you can see I have compromised in order to have a somewhat open floor plan, leaving an open game area to the left of the theater area.
http://i227.photobucket.com/albums/dd153/cuzed2/LayoutSketch.jpg

I have since boxed in the areas (in red) to the LH and RH side of the screen, in the sketch below, this was done to hide utilities in the front RH corner, and (on the left) to keep things symmetrical.
http://i227.photobucket.com/albums/dd153/cuzed2/ScreenStageRough-InQuestion.jpg

The actual photo below is where I am today.
http://i227.photobucket.com/albums/dd153/cuzed2/FrontWall-Soffitts_042808.jpg
I will be adding floor to ceiling bass traps (OC703) in the front corners, and I will be insulating the studs with pink stuff between the studs on the screen wall, and plan to cover the front wall with linacoustic and GOM.

My question: should I also treat the sidewalls immediatly adjacent to the LH and RH side of the screen?

Other info and questions:

The finished ceiling height will be 7'9", the ceiling joists will be stuffed with insulation, and then using the ceiling max system will be finished with acoustical tile.

I am planning on stuffing the soffits with pink stuff, then drywalling the underside and vertical surface of the soffits - Is this a mistake?

I will try to hit the reflection points with panels (at least the RH side). Should I treat the back wall? Would there be any benefit to putting corner traps in the upper rear corners instead? How about corner traps in the upper corenrs of the adjoining game room area?

Thanks in Advance!

OK, I'm in the final stretch in designing my first crack at room treatments. I have a couple of questions related to absorbers that I haven't seen clearly answered.

1) I'm going to build superchunks for all corners that are avail (back right leads to a hallway so no corner there). I am going to build them floor to ceiling, inside a frame for portability and built-in air gap. My question is actually about the size...I've heard people build them with the outer edge being 2' and some doing 2.8' (the difference between cutting 2x4 panels into 8th or 4ths). I was hoping to get by with the 2' outter edge, but I don't have a clear understanding of the performance difference. Anyone have charts showing this possibly?


2) In the back of the room, I am planning to build some bass abosption panels to mount behind the seating area. These will be 4" thick and have a 1.5" air gap between the wall and panel. So we are talking an almost 6" protrusion. Isn't this going to look pretty ugly? How are people doing these thicker panels that makes them look a little less odd?

Thanks,
Affe

Is there a good guide on how to use REW for doing room sound analysis?

I have my carpet and the chairs in, Im going to hook up all my equipment and run tests before I put up acoustical material.

Is there a good guide on how to use REW for doing room sound analysis?

I have my carpet and the chairs in, Im going to hook up all my equipment and run tests before I put up acoustical material.
Been to this page (http://www.hometheatershack.com/roomeq/)? You'll need to register at the Home Theater Shack Forum to get the latest files. There are also help files there, plus links to the forum threads themselves devoted to the software.

My home theater website has now been updated with the whole story of the recently installed chunk traps. Check my sig.

- Jeff

Thanks! Also, thats a great link...the turkey carver is what I should have used for cutting all my insulation!! What a great tool!

Should bass trapping be symmetrical? I can add a couple of bass traps along the right side wall/ceiling connection -- but cannot put them on the left side. Should I do it anyway, or will I create something weird? (I know for mid/high freq absorption symmetry is important.)

Should bass trapping be symmetrical? I can add a couple of bass traps along the right side wall/ceiling connection -- but cannot put them on the left side. Should I do it anyway, or will I create something weird? (I know for mid/high freq absorption symmetry is important.)
Bass trapping does not need to be symmetrical. I have just added some in the front left corner, the front right corner and the front top corner. (See sig.) It has made an INCREDIBLE difference. True, mine is symmetrical with respect to the front L&R, but there is no symmetry from the front to the rear.

- Jeff

Thanks! Also, thats a great link...the turkey carver is what I should have used for cutting all my insulation!! What a great tool!
Thanks.

I seem to have forgotten to link the 3rd page of the bass trap installation . . . try this (http://www.peparsplace.com/Pg%2025%20-%20Cutting%20and%20installing%20bass%20traps,%20pg%203.htm).

You can not make the bottom half of your back wall 4" thick? place a shelf (maybe 6" deep) on it to blend it better with the top half. I would look just like a wall then?

Great point, penngray. I think I might be able to work that after all! :) I will be doing 1" linacoustic all around the room anyway, it wouldn't look too different with a thicker version of the same panel boxes I'd imagine. We'll see what the WAF does with that, eh?!

If I did do this, it would make a 4" thick mineral wool or spin-glass (unfaced) GOM covered absorber about 16' long across the back wall from floor to 38"H. Is this too much, or just right to mitigate the seating position being only 2.5' off the rear wall?

Also, which would be better, the spinglass (JM 3" yellow stuff) or mineral wool (JM 3" dark green/brown stuff)? And I'm assuming I would put a 1" space between the 3" stuff and the wall to make my 4" total?

The help is hugely appreciated!

I'm dying to get installing things (my new Dali speakers arrived this week, to compliment my Ultra 13 :D)

Thanks.

I seem to have forgotten to link the 3rd page of the bass trap installation . . . try this (http://www.peparsplace.com/Pg%2025%20-%20Cutting%20and%20installing%20bass%20traps,%20pg%203.htm).

Hey pepar,

How'd you cut your chunks so uniformly?!

I've used the electric meat cutter knife, but haven't had such nice clean cuts as you... :o

Any tips for a dummy?

Hey pepar,

How'd you cut your chunks so uniformly?!

I've used the electric meat cutter knife, but haven't had such nice clean cuts as you... :o

Any tips for a dummy?

Yours probably look like mine then, lol! :D I used a turkey carver as well. I did draw lines with a heavy marker to follow, but freehanded the actual cut for all the triangles.

Now when I cut two panels in half for 1'x4' panels I did rig up vice of sorts on the edge of my workbench so my saw would follow a perfectly straight line. Those cuts did come out nearly perfectly. I could have done the same for all the triangles, but since they would be hidden behind fabric I didn't want to take the extra time to do it.

Hey pepar,

How'd you cut your chunks so uniformly?!

I've used the electric meat cutter knife, but haven't had such nice clean cuts as you... :o

Any tips for a dummy?
Turkey Carvers for Home Theater Dummies? :D

I used a metal straight-edge to first cut a shallow line and then endeavored to keep the blade(s) vertical as I completed the cut through the piece. It was not easy and my wrist was aching by the end of the cutting session.

Turkey Carvers for Home Theater Dummies? :D

I used a metal straight-edge to first cut a shallow line and then endeavored to keep the blade(s) vertical as I completed the cut through the piece. It was not easy and my wrist was aching by the end of the cutting session.

Just what I figured--your excellence was not due to superior technology which I might also get my hands on, but hard, careful, time-consuming, painful, old-fashioned effort--dang... :rolleyes:

Bass trapping does not need to be symmetrical. I have just added some in the front left corner, the front right corner and the front top corner. (See sig.) It has made an INCREDIBLE difference. True, mine is symmetrical with respect to the front L&R, but there is no symmetry from the front to the rear.

- Jeff

Thanks for the feedback. Mine is symmetrical side to side, but not front to back -- where I have trapping along the front floor/wall connection but in the rear it is across the places where the back wall meets the left wall and where the back wall meets the right wall.

I don't know why I was thinking left right matter more than front back in terms of symmetry -- probably getting confused about the nature of bass.

Just what I figured--your excellence was not due to superior technology which I might also get my hands on, but hard, careful, time-consuming, painful, old-fashioned effort--dang... :rolleyes:
Yea, there was no "easy" button for this task. I might also mention that one of these is an absolute must when working with insulation:

http://www.peparsplace.com/dustfilter.jpg

Yea, there was no "easy" button for this task. I might also mention that one of these is an absolute must when working with insulation:

http://www.peparsplace.com/dustfilter.jpg

Got it! I'm a firm believer also--I get a cold or headache or both every time otherwise.

Any breakthroughs on livening-up your room?

Yes. At only a 2 foot distance, I'd expect you'd have a strong interfering reflection at about 141 Hz. This is because 141 Hz sound will be out of phase by 180 degrees after it travels a total distance of 4 feet. This is assuming incident angle reflection. So the reflection from mains will be a little farther, hence a bit lower in frequency.

This is likely to create a nice notch in your frequency response. :( This isn't the end of the world by any means, but if you have the opportunity to eliminate it from the start, it is a good idea. It will also fix strong early reflections which would be observed at higher frequencies. That's the reason I am recommending a wideband absorber (unfaced fiberglass), and not a membrane bass trap. And if this was your second row back, rather than your only seating row, I'd worry less about it because you'd still have a row of "prime" seats.

I'd also use a 4'x8' panel, since the wavelength is rather large and would therefore involve a larger area of wall for reflection.

Regards,
Terry

Great help, Terry and Ethan! :):):)

One question--if I make my 4" unfaced spinglass or mineral wool panel (3" material with 1" gap) across the back wall 9'W x 38"H can it be from floor up to 38" and still be effective?

I'm trying to avoid placing this mid-wall which will be too high for my WAF.

Is the key simply the amount of area on the wall covered, or is it also important about where on the wall that area is covered for my back wall?

Having it up higher would give better performance stopping potential bass cancellations off the rear wall. If that's not an option, then I'd recommend something thicker and more of a 'chunk style' absorber behind the furniture catching the wall/floor intersection. This will control some of the boominess but won't do much for reflections off the rear.

Bryan

Is the key simply the amount of area on the wall covered, or is it also important about where on the wall that area is covered for my back wall?

Both.

Im converting a tiny spare room into a theater, and due to its size i would imagine it needs a ton of treatment. The room is 13' L x 7.25' wide x 8' H. Seating will be about 10 ft. from the front wall, which makes that about 3 ft. from the back wall. I'll be treating the obvious first reflection points as well as the entire front wall that isn't covered by the screen (which will stretch from wall to wall).

I have a few questions:

1. How should i deal with bass trapping? corner traps dont seem possible as the screen stretches from wall to wall on the front wall, the door is located on the rear right corner and a window the rear left corner. I'll be covering that window, but prefer not to place a bass trap in that corner for aesthetic reasons (unless absolutely necessary).

2. How should i treat the back wall? Same as penngray with the 4" panel? How large of a panel?


Any help is greatly appreciated, thanks in advance for the help.

Im converting a tiny spare room into a theater, and due to its size i would imagine it needs a ton of treatment. The room is 13' L x 7.25' wide x 8' H. Seating will be about 10 ft. from the front wall, which makes that about 3 ft. from the back wall. I'll be treating the obvious first reflection points as well as the entire front wall that isn't covered by the screen (which will stretch from wall to wall).

I have a few questions:

1. How should i deal with bass trapping? corner traps dont seem possible as the screen stretches from wall to wall on the front wall, the door is located on the rear right corner and a window the rear left corner. I'll be covering that window, but prefer not to place a bass trap in that corner for aesthetic reasons (unless absolutely necessary).

2. How should i treat the back wall? Same ass penngray with the 4" panel? How large of a panel?


Any help is greatly appreciated, thanks in advance for the help.
Many times overlooked, there are "corners" formed by walls and the ceiling and walls and the floor.

OK...here is my plan for my currently untreated basement home theater. Please let me know if I'm going terribly wrong somewhere. This is just my starter package, and I think I'm hitting the most important points with this.

1) Superchunk bass traps floor to ceiling in the 3 corners (there is a hallway in what would be the fourth). I will be using OC703 cut into 8 triangles per 2X4 sheet for a 2' face.

I have yet to see a plan exactly like this, but my idea is to build a complete frame for these. I would put a triangle of plywood on the top and the bottom (perhaps one in the middle as well) connected by 1"X0.5" risers in the 3 corners. I will then cover it with muslin or speaker fabric. My intention with this design is to a) allow a 1" air gap between wall and fiberglass and b) allow me to easily move the traps when necessary. And it will be necessary as one will partially block a closet door.

2) Broadband absorbers at the first reflection points of the side walls. These will be 2" of unfaced OC703 seperated from the wall by about 1.5" and covered in muslin or speaker fabric. This will be based on the design found here: http://www.youtube.com/watch?v=iyYUpkpL0gw
I may add more of these at 2nd reflections, but for now this is it.

3) Panel bass traps on the rear wall direclty behind the listeners. My seating is about 5' from the back wall. For these, I'm thinking of going with Ethan's design found here: http://www.ethanwiner.com/BTPlans.gif
I would go for the 1/4" plywood to capture the deep bass. I was also thinking of making these ticker - 4" deep fiber with the assumption that it would increase the absorbsion. Does this sound right?

So that's it I believe. Please let me know where / how I should modify the overall plan or design of any specific pieces. I'm really uncertain on the panel traps I plan to put in the back. I'm also tempted to just go with a design similar to the broadband traps I mentioned in #2 but with FRK backing on the front of the panel and of course the ticker fiber. Thoughts?

Thanks,
Jeff

Hi Jeff,

These panel bass traps on the back wall are not a good idea in your situation. For one thing, the first and strongest frequency of the phase cancellation due to the reflected wave at a 5 foot distance is about 56 Hz, and such traps will have little effect at this low a frequency.

And a panel trap will reflect mid to high frequencies, and therefore not help with early reflections, which occur at these frequencies. I should add the caveat that rear early reflections are less of an issue than side reflections, as the former tend to create less spatial confusion because they are so different in direction. But for most accurate reproduction, they should be eliminated.

Acoustic control tools like panel traps are great, but they must be used under appropriate circumstances. Don't use a hammer when a screwdriver is the correct tool! Or perhaps the better analogy is a medical one, since acoustical design and treatment have their complexities. During surgery, don't use forceps when a retractor is the right tool! :D

Regards,
Terry

Hi Jeff,

These panel bass traps on the back wall are not a good idea in your situation. For one thing, the first and strongest frequency of the phase cancellation due to the reflected wave at a 5 foot distance is about 56 Hz, and such traps will have little effect at this low a frequency.

And a panel trap will reflect mid to high frequencies, and therefore not help with early reflections, which occur at these frequencies. I should add the caveat that rear early reflections are less of an issue than side reflections, as the former tend to create less spatial confusion because they are so different in direction. But for most accurate reproduction, they should be eliminated.

Acoustic control tools like panel traps are great, but they must be used under appropriate circumstances. Don't use a hammer when a screwdriver is the correct tool! Or perhaps the better analogy is a medical one, since acoustical design and treatment have their complexities. During surgery, don't use forceps when a retractor is the right tool! :D

Regards,
Terry

Hi Terry out of curiosity do you do manual calibrations? There are many that believe in just do audyssey and your done.MY HAA calibrator ordered my room treatments the other day and he uses Sencore units to measure the room peaks and dips.Whats your thoughts on Audyssey?

Glenn from GIK acoustics asked me to write something up about how to install Tri-Traps in upper corners when I did mine, because he gets asked how all the time. He simply didn't have any pictures to explain how to do it. Anyway, I made a separate thread on this. Hopefully this forum was the best place for it.

http://www.avsforum.com/avs-vb/showthread.php?t=1025325

This will be based on the Joel DuBay (Realtraps) design found here: http://www.youtube.com/watch?v=iyYUpkpL0gw

Please - No!!!!!!!!

RealTraps is an ethical company that sells high quality products for a fair price. My company has nothing to do with that video, which is a rip-off of the design of another ethical treatment vendor. Joel DuBay has nothing to do with my company, and naming his own company so close to mine is yet another rip-off that has caused such confusion more than once.

I know you didn't mean to confuse the companies intentionally Jeff, but this is a very sensitive issue for me because of all the slimy behavior over many years by said individual above.

--Ethan

Hi Terry out of curiosity do you do manual calibrations? There are many that believe in just do audyssey and your done.MY HAA calibrator ordered my room treatments the other day and he uses Sencore units to measure the room peaks and dips.Whats your thoughts on Audyssey?
Yes, I do manual calibrations. But after room treatment is done. And measurement/calibration may point out the need for further room treatment.

As for Audyssey, I am doing an Audyssey MultEQ Pro calibration next week! In general, I am very impressed with this EQ technology. I've read the journal papers by its developers, Sunil Bharitkar and his Ph.D. advisor, Chris Kyriakakis. I have a reasonably good understanding of the theory behind it. Chris, BTW, is very present on the Official Audyssey Forum here, and is the source for practical info on Audyssey.

Audyssey doesn't replace acoustic treatment, but it fine tunes it.

Regards,
Terry

Yes, I do manual calibrations. But after room treatment is done. And measurement/calibration may point out the need for further room treatment.

As for Audyssey, I am doing an Audyssey MultEQ Pro calibration next week! In general, I am very impressed with this EQ technology. I've read the journal papers by its developers, Sunil Bharitkar and his Ph.D. advisor, Chris Kyriakakis. I have a reasonably good understanding of the theory behind it. Chris, BTW, is very present on the Official Audyssey Forum here, and is the source for practical info on Audyssey.

Audyssey doesn't replace acoustic treatment, but it fine tunes it.

Regards,
Terry

Thankyou for your reply.

Thankyou for your reply.
You're very welcome, Franin. I travel to do calibrations. Could come to Perth, mate. With plane ticket, it would be an expensive calibration.:D But not the most expensive I have done! :D:D

Regards,
Terry

You're very welcome, Franin. I travel to do calibrations. Could come to Perth, mate. With plane ticket, it would be an expensive calibration.:D But not the most expensive I have done! :D:D

Regards,
Terry
He he I could see my wife getting upset, she would prefer a plane ticket to Europe.:D
I have a HAA calibrator at the moment doing mine Terry.He uses sencore.We'e ordered room treatment and looking forward to hear the end results.I have to say there is not many people that know about manual calibrations, they all think put the mic on that is supplied with the unit and you have the perfect sound(far from it, I reckon).if anything you guys are top when it comes to HT, because after you guys are finished I've never heard my subs sound so smooth and tight everthing was perfect.

Joel DuBay has nothing to do with my company, and naming his own company so close to mine is yet another rip-off that has caused such confusion more than once.

Sorry Ethan - I changed my post to remove that info. I usually don't trust something I see in a youtube vid, but I wasn't expecting someone to misrepresent their affiliation with your company.

And a panel trap will reflect mid to high frequencies, and therefore not help with early reflections, which occur at these frequencies.
Thanks for the correction Terry. Any suggestions on what I use for the first reflections instead? And I went for the traps on the back wall with the thought of 'the more bass traps the better' and I'd heard it was important to treat them behind the listening spot. Any alternate suggestions??

Thanks...
Jeff

SAny suggestions on what I use for the first reflections instead? And I went for the traps on the back wall with the thought of 'the more bass traps the better' and I'd heard it was important to treat them behind the listening spot. Any alternate suggestions??
Most of us use - successfully - 2" Owens Corning 703. Some use 4", but that can become an aesthetic issue and still doesn't reach into bass trap absorption frequencies. 1" is, IMO, too thin to be considered broadband absorption.

Just my $.02.

Most of us use - successfully - 2" Owens Corning 703. Some use 4", but that can become an aesthetic issue and still doesn't reach into bass trap absorption frequencies. 1" is, IMO, too thin to be considered broadband absorption.

Thanks pepar. It sounds like we are on the same page. I was trying to figure out what Terry was telling me and I realized I may have used the wrong terminology in my original post. Does 'panel trap' imply the use of a membrane such as plywood with absorbsion material behind it? As I tried to describe, I was just planning on tossing up a 2" thick piece of OC703 with a 1" air gap behind it. I said panel because its a flat object.

With this clarification, does this sound correct for a broadband first reflection absorber? What is the appropriate terminology for this type of....ummm...panel?

Thanks,
Jeff

What purpose does the air gap between the panel and wall serve? I'd like to build some panels with as little depth as possible.

Sorry for the newb question, and thanks in advance for the response.

In general, air does not move at the wall. Standing waves 'vibrate' such that the air at the wall has no motion, and the air moves more and more (towards and away from the wall) as you move further from the wall, until you hit the 'peak' (1/4 wavelength of the frequency of sound you are talking about).

Therefore, the maximum air movement for any given frequency is at 1/4 of the wavelength off the wall.

The panels are designed to 'slow down' this movement. They are more effective the faster the air is moving (they can't slow down air that isn't moving right at the wall).

A thick panel solves this because the outer part of the panel is pretty far from the wall and slows down the air most effectively near the outer surface. The part of the panel near the wall isn't as effective as the air isn't moving much there.

You can make a panel more effective at lower frequencies (1/4 wavelength is bigger) if you move the panel a few inches off the wall where the air is moving more...

paul

In general, air does not move at the wall. Standing waves 'vibrate' such that the air at the wall has no motion, and the air moves more and more (towards and away from the wall) as you move further from the wall, until you hit the 'peak' (1/4 wavelength of the frequency of sound you are talking about).

Therefore, the maximum air movement for any given frequency is at 1/4 of the wavelength off the wall.

The panels are designed to 'slow down' this movement. They are more effective the faster the air is moving (they can't slow down air that isn't moving right at the wall).

A thick panel solves this because the outer part of the panel is pretty far from the wall and slows down the air most effectively near the outer surface. The part of the panel near the wall isn't as effective as the air isn't moving much there.

You can make a panel more effective at lower frequencies (1/4 wavelength is bigger) if you move the panel a few inches off the wall where the air is moving more...

paul

So would 4" of OC703 right next to the wall be better or worse than a 2" panel 2" out from the wall for first reflection points?

So would 4" of OC703 right next to the wall be better or worse than a 2" panel 2" out from the wall for first reflection points?

I'll defer to the experts, but my take:

First reflection point treatment is generally about making sure that your ears correctly identify the location of sounds coming from the front speakers. Mid to high frequency sounds travel (generally) in straight lines and bounce off of things like rays of light. The direct sound and the first reflection sound off the side wall hit your ear around the same time and muddle the direction the sound came from.

The important point in the above is "mid-to-high frequency sound". Low frequency sound generally does not travel in such nice light ray paths, and isn't easy to localize (hence your subwoofer can be shoved anywhere in the room and it doesn't make you think all the bass is coming from that direction).

Therefore: first reflection point treatment is about mid-high frequencies. 1-2" of treatment is plenty for that.

For bass traps, filling a separate treatment function, you want to absorb very low frequencies (as low as you can go). Thicker treatment or treatment spaced off of the wall help with this.

Those are sort of the two ends of the spectrum: thin mid-high absorption for FRP, thick low frequency absorption for bass traps.

The other treatment often done is 'broadband absorption', 2-4" thick stuff that is trying to knock down the rt60 (echo decay time) of the room as evenly as possible across the frequencies. It's not uncommon to see thicker than 1" at first reflection points, but in general it's not because the first reflection points need it, it's because it works just fine to knock down the first reflection and is also a bit more effective at evenly absorbing lower frequencies. Two birds with one stone.

In general, air does not move at the wall. Standing waves 'vibrate' such that the air at the wall has no motion, and the air moves more and more (towards and away from the wall) as you move further from the wall, until you hit the 'peak' (1/4 wavelength of the frequency of sound you are talking about).

Therefore, the maximum air movement for any given frequency is at 1/4 of the wavelength off the wall.

The panels are designed to 'slow down' this movement. They are more effective the faster the air is moving (they can't slow down air that isn't moving right at the wall).

A thick panel solves this because the outer part of the panel is pretty far from the wall and slows down the air most effectively near the outer surface. The part of the panel near the wall isn't as effective as the air isn't moving much there.

You can make a panel more effective at lower frequencies (1/4 wavelength is bigger) if you move the panel a few inches off the wall where the air is moving more...
Paul, I was under the impression that absorbers were most effective at bass frequencies the closer they are to the wall because the air is moving more slowly and the waves are easier to impede. Standing a panel off the wall produces a diaphramatic effect that extends the absorption to lower frequencies, but more than an inch of standoff, though, and the effectiveness because of the first point lessens.

-Jeff

Thanks pepar. It sounds like we are on the same page. I was trying to figure out what Terry was telling me and I realized I may have used the wrong terminology in my original post. Does 'panel trap' imply the use of a membrane such as plywood with absorbsion material behind it? As I tried to describe, I was just planning on tossing up a 2" thick piece of OC703 with a 1" air gap behind it. I said panel because its a flat object.

With this clarification, does this sound correct for a broadband first reflection absorber? What is the appropriate terminology for this type of....ummm...panel?

Thanks,
Jeff
To me, "trap" means bass trap. The panels you mention I would call broadband absorbers. "Broadband" may seem to imply all frequencies, but not in acoustical treatment parlance. Corner bass traps are still required to reach the lowest frequencies. A 1" standoff can lower the lowest effective frequency of a panel through a diaphram effect, i.e. instead of absorbing from impeding the vibration of the air molecules, it absorbs by vibrating as a panel.

FWIW, I did not want my panels encroaching into my room any more so they are tight against the wall. Besides, I have bass traps for the bottom frequencies. And absorbers in the corners are much more effective at lower frequencies than panels, stood off or not, mounted on a wall.

- Jeff

FWIW, I did not want my panels encroaching into my room any more so they are tight against the wall. Besides, I have bass traps for the bottom frequencies. And absorbers in the corners are much more effective at lower frequencies than panels, stood off or not, mounted on a wall.

OK, I'm feeling a lot more confident about this after reading your posts. Might be we are in synch sharing the same name and all :D

Based on what you are saying, I think I will build my broadband absorbers with the lowest profile frame as possible, to minimize the airgap and focus on the mid-high frequencies. These will be 2" for the same reason.

For the LF, I will be counting on those superchunk traps. I'm still not postive this is the best route to go, but I think I will space those about 1" to increase the distance of the outside of the trap and thus get down to some lower frequencies.

At this point, I'm not sure what I'm going to do on that back wall, if anything.

BTW - love the step by steps on your site - very helpful.

Thanks,
Jeff

Paul, I was under the impression that absorbers were most effective at bass frequencies the closer they are to the wall because the air is moving more slowly and the waves are easier to impede. Standing a panel off the wall produces a diaphramatic effect that extends the absorption to lower frequencies, but more than an inch of standoff, though, and the effectiveness because of the first point lessens.

-Jeff
Paul gave some excellent answers. For a wave which hits the wall at a normal angle, the wave velocity is highest at the 1/4 wavelength distance from the wall. It is zero right at the wall because the rigid wall prevents the air from moving.

Now, there is a significant difference between a bass absorber with and without a diaphragm on its front surface. A diaphragm is anything from a thin membrane, like a facing of FRK, to a panel of plywood.

Staying for the moment with a non-diaphragm bass trap, one whose surface is a porous absorber like the rest of it, this is a velocity type absorber. Air has to physically move between the open pores of the absorber for the absorber to work. And without velocity, there is no air movement.

So for a pure porous bass absorber, the deeper the better (in general), and the farther from the wall the better for low frequencies.

A diaphragmatic absorber is a more complicated beast. This is a pressure type absorber, and pressure is greatest right at the wall surface! But this type of absorber also requires depth, because once the diaphragm translates pressure into velocity, you are back to a porous absorber which needs depth to absorb low frequencies.

Hope this helps.

Regards,
Terry

This question may have been asked several times in this thread already, but I have not been able to find the answer with searching. :(

I want to treat the first reflection point for my center channel. I know rule of thumb is you need at least two inches thick of an adequate treatment material to do an adequate job.
I have some leftover knauf that is 1” thick from my theater build a few years ago. Can I just double up two pieces of knauf and get the same performance as 1 panel of 2” OC 703 or 705 that is always recommended?
Or should I just buy some 705 and use that?
Another slightly off topic question. For those that have used 703 and 705, it seems like the lighter yellowish color of the insulation would show through black GOM. Especially when light hits it. My center is VERY close to the ceiling. Because I will have to put the panel somewhat close to the screen. This is a big concern for me.

Thanks in advance.

This question may have been asked several times in this thread already, but I have not been able to find the answer with searching. :(

I want to treat the first reflection point for my center channel. I know rule of thumb is you need at least two inches thick of an adequate treatment material to do an adequate job.
I don't know where this "rule of thumb" came from, but you need only 1" of efficient absorber, like semi-rigid fiberglass, to specifically treat early reflections.

Regards,
Terry

I don't know where this "rule of thumb" came from, but you need only 1" of efficient absorber, like semi-rigid fiberglass, to specifically treat early reflections.

Regards,
Terry


Well thank you Terry. :) Ask and yea shall receive a prompt answer. :)
Well, I have read many times that 2 inch is best for first reflection points because it takes care of the highs and mid range frequencies better than 1 inch.
I was not expecting anyone to tell me that 1" would be sufficient. So would my knauf be sufficient to use as a first reflection point absorber for my center channel?
Would I get better performance if I doubled it?

Thank!!!

Well thank you Terry. :) Ask and yea shall receive a prompt answer. :)
Well, I have read many times that 2 inch is best for first reflection points because it takes care of the highs and mid range frequencies.
I was not expecting anyone to tell me that 1" would be sufficient. So would my knauf be sufficient to use as a first reflection point absorber for my center channel?
Would I get better performance if I doubled it?

Not for specific control of early reflections. It is hard to know whether your room would benefit from the extended lower frequency absorption of 2" material without acoustical measurements and analysis.

Regards,
Terry

Another slightly off topic question. For those that have used 703 and 705, it seems like the lighter yellowish color of the insulation would show through black GOM. Especially when light hits it. My center is VERY close to the ceiling. Because I will have to put the panel somewhat close to the screen. This is a big concern for me.

Thanks in advance.

No, it does not show through at all. 100% opaque.

Terry,

Can I get a bit of clarification, please?

I noticed that earlier in this thread you suggested, when using this method, you prefer 2" of semi-rigid fiberglass on the front wall as opposed to 1". In the post above, I believe you have also said this many times before, you tell us that 1" inch is sufficient for early reflection points.

Can you help me better understand why the front wall needs to be "deader" than the first reflection points along the side walls? I know that this helps imaging but I'm not quite understanding how that happens. How much improvement will the extra inch of semi-rigid fiberglass offer? I have some extra and wonder if I should go ahead put it up since I'm still in the building phase.

I have already built and installed the "chunk style" or "wedge" bass traps (24x17x17) in the front-side corners and have 1" Linacoustic covering the entire front wall. The side walls (at the moment) have 1" Linacoustic from the floor to 49". The rear wall is bare. The room is 13x21.2x7.5. The floor is not carpeted yet but that will go down over the heart pine as soon as the A/C is complete next week.

My room images very well, as it is now, and I am certain the sound will change quite a bit once the carpet is down. I suspect that I may need to reduce the amount of linacoustic on the side walls. Any suggestions you might have are greatly appreciated.

Thanks,
Dan

Any suggestions on what I use for the first reflections instead? And I went for the traps on the back wall with the thought of 'the more bass traps the better' and I'd heard it was important to treat them behind the listening spot. Any alternate suggestions??

Thanks...
Jeff
Hi again Jeff,

Specifically for first reflections, you need only 1" of fiberglass or equivalent absorber. But with only 5 feet to your back wall, you have other problems. :(

You are likely to have some low frequency notches starting pretty far down. Use as much absorption depth, and/or space the absorber as far from the wall as humanly possible, or as WAF will allow! :)

Regards,
Terry

Thanks for the response Terry.

With the 5' issue...would I be better off violating the 38% guideline and moving the couch further up? I would also consider building free standing frames for the panels and putting them just behind the listener, but it may get in the way of the A/V rack.

Here's a pic of my layout roughly.
http://picasaweb.google.com/jrames/TheaterPics/photo#5196182471775025394

The speaker layout is approximate, and is going to change as I test / add absorbers. I don't have all of the relative distances in there, but the listeners ears are just about 5' from that rear wall as I stated. The main theater area is 18x21 with 81" ceilings (yes, its like a hobbit cave). Most of the remaining area is enclosed with drywall, except for that hallway just to the bottom right of the theater area and the nook leading into the stairway.

Jeff

Hi Jeff,

You realize that acoustical consulting is my sole source of income (I don't sell any treatment products), right? :D

I am more than happy to provide general treatment guidlines, tips, etc. But at some point, one gets into more detailed design, everything interacts with everything else, and one cannot isolate just one piece of a design and provide a "sound" recommendation. For that I need much more information and would have to devote significant time resources to analyze it. It is like an MD giving diagnosis and treatment over the web. This is not a good idea, and to some degree, constitutes malpractice because a detailed medical exam has not been performed.

Feel free to take the advice of others. But it is really hard for me to weigh in any further as a profession without quite possibly being off base, and compromising my standards. Hope you understand. :(

Regards,
Terry

Not for specific control of early reflections. It is hard to know whether your room would benefit from the extended lower frequency absorption of 2" material without acoustical measurements and analysis.

Regards,
Terry
Terry,

One inch absorption falls off dramatically under 1k compared to 2". Shouldn't first reflection point absorbers go at least to 500Hz? And don't most spaces used for home theaters benefit, generally, from the additional absorption down to ~250Hz of the 2"?

- Jeff

Feel free to take the advice of others. But it is really hard for me to weigh in any further as a profession without quite possibly being off base, and compromising my standards. Hope you understand. :(

No problem. I was actually posting the layout and specifics for everyone to comment on. The only reason I asked for some specific clarification was because you'd given me some specific advice. Point taken...

Terry,

One inch absorption falls off dramatically under 1k compared to 2". Shouldn't first reflection point absorbers go at least to 500Hz? And don't most spaces used for home theaters benefit, generally, from the additional absorption down to ~250Hz of the 2"?

- Jeff
I have found that in practice, 1" thick rigid or semi-rigid fiberglass is completely adequate to sufficiently attenuate early reflections as measured by an energy energy time curve.

Regards,
Terry

...also, some current research suggests that diffusion can be appropriate for early reflections. This decision would hinge upon the quality of the off axis response of the specific speaker being used.

Terry, Bryan, Ethan,

Need your input on the post below. I have a dywaller coming soon, and I need to decide if I should drywall, or treat the walls immediatly adjacent to my screen.

My screen wall will be treated with 6" of insulation (possibly with 2" of OC if you reccomend) and covered with 1" linacoustic, and GOM.

The vertical front corners will include floor to ceiling Basstraps, 17x17x24.
I will also be making panel(s) to cover my first reflection points about 7' away from the screen.

Not sure with my semi-open floorplan >> if there is much advantage to covering the first 3~5 feet of sidewall adjacent to my screen...?

Thanks In Advance,
Craig


Question(s) for the acoustic experts that are lurking...

The sketch below is the layout of my theater area. As you can see I have compromised in order to have a somewhat open floor plan, leaving an open game area to the left of the theater area. I have since boxed in the areas (in red) to the LH and RH side of the screen, in the sketch below, this was done to hide utilities in the front RH corner, and (on the left) to keep things symmetrical.
http://i227.photobucket.com/albums/dd153/cuzed2/ScreenStageRough-InQuestion.jpg

The actual photo below is where I am today.
http://i227.photobucket.com/albums/dd153/cuzed2/FrontWall-Soffitts_042808.jpg
I will be adding floor to ceiling bass traps (OC703) in the front corners, and I will be insulating the studs with pink stuff between the studs on the screen wall, and plan to cover the front wall with linacoustic and GOM.

My question: should I also treat the sidewalls immediatly adjacent to the LH and RH side of the screen?

Other info and questions:

The finished ceiling height will be 7'9", the ceiling joists will be stuffed with insulation, and then using the ceiling max system will be finished with acoustical tile.

I am planning on stuffing the soffits with pink stuff, then drywalling the underside and vertical surface of the soffits - Is this a mistake?

I will try to hit the reflection points with panels (at least the RH side). Should I treat the back wall? Would there be any benefit to putting corner traps in the upper rear corners instead? How about corner traps in the upper corenrs of the adjoining game room area?

Thanks in Advance!

Not sure with my semi-open floorplan >> if there is much advantage to covering the first 3~5 feet of sidewall adjacent to my screen...?

Thanks In Advance,
Craig
Yes, I would build it out as much as possible. Symmetry at the front of the room can make a big difference in the evenness of sound from your front speakers.

Regards,
Terry

Not sure with my semi-open floorplan >> if there is much advantage to covering the first 3~5 feet of sidewall adjacent to my screen...?

I agree with Terry that symmetry is important, especially in the front part of the room. Also, the side walls reflection points probably extend further back in the room, so be sure to treat back far enough. Likewise, the ceiling reflection points. The rear wall can be a source of "early" reflections if it's closer than 10 feet from any seats. The rear wall is also a prime source of peaks and nulls at low frequencies.

--Ethan

Terry, Bryan, Ethan,

Need your input on the post below. I have a dywaller coming soon, and I need to decide if I should drywall, or treat the walls immediatly adjacent to my screen.
I don't think "or" is the right question. Drywall and then treat.

Terry,

Can I get a bit of clarification, please?

I noticed that earlier in this thread you suggested, when using this method, you prefer 2" of semi-rigid fiberglass on the front wall as opposed to 1". In the post above, I believe you have also said this many times before, you tell us that 1" inch is sufficient for early reflection points.

Can you help me better understand why the front wall needs to be "deader" than the first reflection points along the side walls? I know that this helps imaging but I'm not quite understanding how that happens. How much improvement will the extra inch of semi-rigid fiberglass offer? I have some extra and wonder if I should go ahead put it up since I'm still in the building phase.

I have already built and installed the "chunk style" or "wedge" bass traps (24x17x17) in the front-side corners and have 1" Linacoustic covering the entire front wall. The side walls (at the moment) have 1" Linacoustic from the floor to 49". The rear wall is bare. The room is 13x21.2x7.5. The floor is not carpeted yet but that will go down over the heart pine as soon as the A/C is complete next week.

My room images very well, as it is now, and I am certain the sound will change quite a bit once the carpet is down. I suspect that I may need to reduce the amount of linacoustic on the side walls. Any suggestions you might have are greatly appreciated.

Thanks,
Dan
Sorry I missed your question earlier, Dan.

Basically, early reflection image problems happen at medium to high frequency. At these frequencies, your speakers are mostly radiating forward, not omnidirectionally. So early reflections travelling backwards from speakers to the front wall are not an issue. They certainly can be for the side walls, ceiling, and floor, depending on the directivity and positions of your front speakers.

The thicker absorption at the front wall is to help deal with low frequency reflections, which are much more omnidirectional. In fact, at subwoofer frequencies emanating from a typical subwoofer-sized box, the sound radiation is perfectly omnidirectional.

Now, 2" isn't going to get you much into the subwoofer range at all. But it is a good practical compromise for most people. It will help a lot with potentially interfering reflections in the 3 figures of hertz, which will be fairly omnidirectional.

Regards,
Terry

Terry,

Thanks for the answers. That helps clear it up somewhat.

Given the limited information I have already provided, do you feel my room would benefit from the extra inch of linacoustic on the front wall or are the "wedge" bass traps and 1" sufficient? If the extra inch will make a difference, what difference(s) should I expect and/or notice?

Thanks,
Dan

Terry,

Thanks for the answers. That helps clear it up somewhat.

Given the limited information I have already provided, do you feel my room would benefit from the extra inch of linacoustic on the front wall or are the "wedge" bass traps and 1" sufficient? If the extra inch will make a difference, what difference(s) should I expect and/or notice?

Thanks,
Dan
I'd recommend using an extra inch on the front wall, if you have the fiberglass. This will not affect imaging, but can improve the response (reduce coloration) in above-subwoofer frequency bass. I cannot tell you what you will personally experience or notice. But I would expect there to be some measurable improvement in the steady-state frequency response.

Regards,
Terry

Terry,

Thanks again! I have plenty of spare linacoustic so I'll put an another inch up tomorrow while the A/C guys are installing the ductwork.

Thanks,
Dan

Re 1" or 2":
Early reflections are defined as reflections from boundary surfaces or other surfaces in the room which reach the listening area within the first 15 ms after the arrival of the direct sound. The levels of these reflections should be at least 10 dB below the level of the direct sound for all frequencies in the range 1 kHz to 8 kHz.

from: EBU Tech. 3276 – 2nd edition

Thanks for bringing up this reference, Bob. At 1 kHz, 1-inch of rigid or semi-rigid fiberglass will absorb about 90+% of the energy incident upon it. This corresponds to a drop in reflected energy of 10 dB or more. Since the position of the early reflection surfaces are off-axis, they will get somewhat less than the full on-axis response, and the reflection will be even weaker. Hence 1-inch fiberglass is more than enough to sufficiently reduce early reflections.

Or just try it. It works. :)

Regards,
Terry

For a room with all wall, floor and ceiling surfaces of 8"-20" of concrete, how does 2" front insulation (AT screen), 4" ceiling, 6" rear, 2" sides up to 48" and two 24"x24"x34" super chunks in the front corners sound? The local supplier has Rockwool RHT 40:

RHT 40 2" (51mm) 3.5 pcf (56 kg/m3) 0.26 0.68 1.14 1.13 1.06 1.07 1.00
RHT 40 4" (100mm) 3.5 pcf (56 kg/m3) 1.07 1.01 1.07 1.06 1.07 1.16 1.05

To get 4" and 6" I'll be layering 2" 4'x8' sheets.

The walls have eight 20" wide columns made of 1" MDF (about 20%-30% of the side and back wall surface area is MDF with no treatment) and 1' wide soffit around the room's ceiling, made of MDF with 7" of crown made of the ultralight decorative molding (so really only 5" of flat face on the soffit is exposed). Between the columns will be thin fabric (to be picked) to let most sound through to get some reflections above ear level.

Because of water problems, all insulation and columns are held 1" off the wall to allow water to flow behind it to drains and there is no framing or drywall except near the entry into the room. Carpet is outdoor carpet/commercial like that can get wet and not very thick.

I've bought a feedback pro, test microphone, mixer, and all the other equipment to do testing but before I buy all this insulation I wanted to make sure I was fairly close on my choices.

I will be getting some paper to adhere to possibly the back wall or ceiling insulation to reflect highs. The main reason for all the insulation is try to kill the massive amounts of bass that the cement walls will reflect. That's why I'm looking at 2" min on walls, so I can get something with over a 1.x noise reduction in the bass range and evenly kill everything rather than taking too much highs but not bass.

For audio equipment it will likely be the Denon AVR-4308CI with 140Watts per channel in a 7.1 configuration and RBH or Energy speakers. Two subs, yet to be picked.

http://i261.photobucket.com/albums/ii57/distoga/IMG_0720.jpg
(Column will be covered in Dazian celtic cloth so they look full height and surround speakers will be placed in some columns)

I just got a price quote for the insulation for my room and it was well over a grand... :O I can get linacoustic RC for nearly a forth of the price and other threads say linacoustic is fairly close to 703 even though linacoustic is slightly less dense? How about a rear wall with three 2" linacoustic layers to get the 6"?, ceiling done with linacoustic (or atleast one of two layers with it) and everything but the bass traps in 2" linacoustic, also maybe do 17x17x24 rather than 24x24x34 bass traps?

Terry,

I placed the extra inch of linacoustic on the front wall this morning and had a chance to check out the sound briefly. The A/C guys took an hour for lunch so I didn't have a lot of time. It definitely improved the quality of the mids and high bass. The room sounds "deader" overall. I guess I was getting a bit of resonance from the screen or something but whatever it was, that is gone. Is this the "coloration" you mentioned?

Anyway, THANKS!!!!! The room sounds better.

...also, some current research suggests that diffusion can be appropriate for early reflections. This decision would hinge upon the quality of the off axis response of the specific speaker being used.

as in, the greater off axis speaker response, the more applicable diffusion types of treatment might be? or would it be the converse, i.e., absorption more often applicable?

as in, the greater off axis speaker response, the more applicable diffusion types of treatment might be? or would it be the converse, i.e., absorption more often applicable?
I believe Dennis is referring to Toole's recent work. If so, it's as in the flatter the off-axis response, the more diffusion may be better than absorption. Or no treatment at all. This applies only to lateral reflections.

Not exactly the flatter the off axis response ...

You'd expect response to roll off as you go off axis...good off axis response would mean the shape of the response curves would be the same except for the roll off.

Let me put my question another way, in hopes of eliciting a response that even my feeble mind can grasp. :D...

To put it more simply, the better your speakers are at providing good sound outside of the "sweet spot" (or at least, similar sound to what you hear in the sweet spot), the more applicable the diffusion or 'no treatment at all' tactics might be for those particular speakers?

For example, I've been considering the purchase of some Ascend Sierra speakers, which have a design priority for just that, to sound just as good or very nearly as good from more than just the primary seating location, as opposed to some other speaker designs which are designed to sound great in the "sweet spot", but fall down a bit more when the listener is positioned in other secondary seating locations.

Let me put my question another way, in hopes of eliciting a response that even my feeble mind can grasp. :D...

To put it more simply, the better your speakers are at providing good sound outside of the "sweet spot" (or at least, similar sound to what you hear in the sweet spot), the more applicable the diffusion or 'no treatment at all' tactics might be for those particular speakers?

For example, I've been considering the purchase of some Ascend Sierra speakers, which have a design priority for just that, to sound just as good or very nearly as good from more than just the primary seating location, as opposed to some other speaker designs which are designed to sound great in the "sweet spot", but fall down a bit more when the listener is positioned in other secondary seating locations.
I think the off axis we're talking about with regards to treating the left and right front first reflection points is much further off axis than a few seats left and right of a sweet spot. Beyond that, I don't think it's knowable in advance of installing the Ascends in your theater whether they will sound better with absorbers, diffusors or nothing at those points.

Just my feeble $.02. :)

IMO, very very few speakers have the kind of smooth, identical off-axis response to qualify. When you consider how many seats we're talking about and the severe off axis waves that are reflected to seating, IMO, absorbtion is still appropriate 99% of the time.

As for the front wall, while there are no mid and high frequency issues from the mains, thicker absorption can absolutely be used to tame SBIR issues - or - NOT used to deliberately allow SBIR to be USEFUL in compensating for anomolies caused by other issues that may not be able to be dealt with any other way.

This is where what Terry was saying earlier comes into play. It's great to get general recommendations but to really get into the details takes a lot of information and a lot of work doing an analysis.

Bryan

Terry,

I placed the extra inch of linacoustic on the front wall this morning and had a chance to check out the sound briefly. The A/C guys took an hour for lunch so I didn't have a lot of time. It definitely improved the quality of the mids and high bass. The room sounds "deader" overall. I guess I was getting a bit of resonance from the screen or something but whatever it was, that is gone. Is this the "coloration" you mentioned?

Anyway, THANKS!!!!! The room sounds better.
You are very welcome, Dan. Glad this worked for you!

Regards,
Terry

Not exactly the flatter the off axis response ...

You'd expect response to roll off as you go off axis...good off axis response would mean the shape of the response curves would be the same except for the roll off.
Yup. And most speaker manufacturers (especially at the high, very expensive end) just hate to make public their off-axis responses. They are often less than ideal.

Regards,
Terry

Will this type of Material be as absorbent as the other JM acoustic insulation mentioned here? Here is the link...

http://www.jm.com/insulation/performance_materials/products/ei4_microlite.pdf

Also, off axis response has to account for 'toe in' of the speakers. So a good off axis response facing forward might not be if you prefer to 'toe in' your speakers.

Bob

I think the off axis we're talking about with regards to treating the left and right front first reflection points is much further off axis than a few seats left and right of a sweet spot. Beyond that, I don't think it's knowable in advance of installing the Ascends in your theater whether they will sound better with absorbers, diffusors or nothing at those points.

Just my feeble $.02. :)

IMO, very very few speakers have the kind of smooth, identical off-axis response to qualify. When you consider how many seats we're talking about and the severe off axis waves that are reflected to seating, IMO, absorbtion is still appropriate 99% of the time.




I'm not building a home theater. I'm just here to absorb more info on acoustic treatments in general.

So if I'm reading you both correctly, then sidewall diffusion or even no treatment at all on side walls could be within the realm of possibility for less taxing environments (those rooms which aren't very large across, nor having to contend with several rows/columns of seating, etc., coupled with owning that rare speaker which performs smoothly enough off-axis in the ways being described here).

So, still.. probably not very likely, but at least something to bare in mind (that treating side wall first reflections shouldn't be considered an automatic absolute given). In other words, MOST rooms of any kind would need sidewall first reflection absorption, but there are those occasional exceptions where this won't be necessary. So don't force yourself to keep absorption treatments in place if you find that it doesn't sound as good as without because it just might not sound as good, afterall.

Hope I got this right. :p

I'm not building a home theater. I'm just here to absorb more info on acoustic treatments in general.

So if I'm reading you both correctly, then sidewall diffusion or even no treatment at all on side walls could be within the realm of possibility for less taxing environments (those rooms which aren't very large across, nor having to contend with several rows/columns of seating, etc., coupled with owning that rare speaker which performs smoothly enough off-axis in the ways being described here).

So, still.. probably not very likely, but at least something to bare in mind (that treating side wall first reflections shouldn't be considered an automatic absolute given). In other words, MOST rooms of any kind would need sidewall first reflection absorption, but there are those occasional exceptions where this won't be necessary. So don't force yourself to keep absorption treatments in place if you find that it doesn't sound as good as without because it just might not sound as good, afterall.

Hope I got this right. :p
Most people have NO acoustical treatments. That they're on your list puts you ahead of the game already. If you're going it alone (w/o a pro), then go slow. FWIW, in my room with my rear (money) row 6' from the rear wall, the absorber that made, by far, the biggest improvement in sound was the one on the rear wall. Getting rid of that 12ms delayed reflection was a real eye-(and ear-)opener.

The new thinking by some regarding diffusion or nothing on the front side walls is just that - new. Though it's being put forth by well-respected acoustician, I think most people you'll find here are still firmly in the "treat it" camp.

[QUOTE=pepar;13809562]FWIW, in my room with my rear (money) row 6' from the rear wall, the absorber that made, by far, the biggest improvement in sound was the one on the rear wall. Getting rid of that 12ms delayed reflection was a real eye-(and ear-)opener.[QUOTE]

Hey Pepar,

What did you do for your rear absorber (materials, thickness, dimension, wall placement)? Sorry if you said earlier...

I'm only 3' off the back and I'm experienceing some serious "notches" (per Terry/Ethan/Bryan) in my bass response. :(

Thanks man,
Phil

Hey Pepar,

What did you do for your rear absorber (materials, thickness, dimension, wall placement)? Sorry if you said earlier...

I'm only 3' off the back and I'm experienceing some serious "notches" (per Terry/Ethan/Bryan) in my bass response. :(

Thanks man,
Phil
My absorbers are 2" Owens Corning SelectSound Black.

I'm not building a home theater. I'm just here to absorb more info on acoustic treatments in general.

So if I'm reading you both correctly, then sidewall diffusion or even no treatment at all on side walls could be within the realm of possibility for less taxing environments (those rooms which aren't very large across, nor having to contend with several rows/columns of seating, etc., coupled with owning that rare speaker which performs smoothly enough off-axis in the ways being described here).

So, still.. probably not very likely, but at least something to bare in mind (that treating side wall first reflections shouldn't be considered an automatic absolute given). In other words, MOST rooms of any kind would need sidewall first reflection absorption, but there are those occasional exceptions where this won't be necessary. So don't force yourself to keep absorption treatments in place if you find that it doesn't sound as good as without because it just might not sound as good, afterall.

Hope I got this right. :p

Actually, just the opposite. Diffusion could be used in LARGER environments and with speakers that have exceptional off axis sperformance. Absorbtion is needed if either or both of those conditions are not met. IMO, no treatment at side wall reflections in any normal sized residential enivornment is not a viable option.

Bryan

Also, off axis response has to account for 'toe in' of the speakers. So a good off axis response facing forward might not be if you prefer to 'toe in' your speakers.

All the "toe-in" will do, is change the axis from which the side wall reflections reach the ears from the speaker (well, axis and dB).

Cruel...
Speakers don't know if they are in a home theater or some other type of environment. Acoustic treatments are dictated by the room, seating, speaker characteristics, etc. All rooms require some form of acoustic treatment. In a typical residential sized space, on the order of 80% of the sound you hear is NOT coming directly from the speakers ... it's coming from the room. That's a significant share (good or bad). At the end of the day, no speaker ($80K or otherwise) and no magic electronic device can overcome the effects of the room, nor violate the rules of physics.

I am just venturing into the area of bass traps after folks suggested that bass traps is the way to go to take care of peaks and dips instead of parametric EQ.
I noticed that OC 703, Rockwool 60 etc only start from 125Hz.
I was wondering what other material I could consider if I have to
cover from say 30hz to 200Hz. Any feedback is appreciated
Thanks

I am just venturing into the area of bass traps after folks suggested that bass traps is the way to go to take care of peaks and dips instead of parametric EQ.
I noticed that OC 703, Rockwool 60 etc only start from 125Hz.
I was wondering what other material I could consider if I have to
cover from say 30hz to 200Hz. Any feedback is appreciated
Thanka
Those numbers are for sheets. When bass traps are constructed like this (http://forum.studiotips.com/viewtopic.php?t=535), they reach lower. Also, check the link in my sig as I just installed some.

I noticed that OC 703, Rockwool 60 etc only start from 125Hz.

That's because most labs that measure absorbers are not certified to report below 100 Hz. This doesn't mean the materials suddenly stop working below that frequency. Much more info here if you care:

http://www.realtraps.com/art_testing.htm

--Ethan

pepar, ethan thanks for the explanation.

I am considering the rockwool as people say that it is cheaper than the OC703. Also I can get the rockwool panels in 4'' thickness where as the 703 only comes in 1 or 2'' thickness.

Now my question is whether I should get the rockboard or the RHT.
I guess the rockboard is rigid where as the RHT is semi rigid. I may not cut them into triangles. I am going to just place the panels at the corner and sides. If that is promising then I will take the trouble of cutting.

Also I prefer to order either the rockwool or OC703 online instead of hunting down a local dealer, arranging for a transport etc. Is there a reliable online place for either of these? One of my coworkers has already done a lot of search and I dont think he found an online place.

Thanks

pepar, ethan thanks for the explanation.

I am considering the rockwool as people say that it is cheaper than the OC703. Also I can get the rockwool panels in 4'' thickness where as the 703 only comes in 1 or 2'' thickness.

Now my question is whether I should get the rockboard or the RHT.
I guess the rockboard is rigid where as the RHT is semi rigid. I may not cut them into triangles. I am going to just place the panels at the corner and sides. If that is promising then I will take the trouble of cutting.

Also I prefer to order either the rockwool or OC703 online instead of hunting down a local dealer, arranging for a transport etc. Is there a reliable online place for either of these? One of my coworkers has already done a lot of search and I dont think he found an online place.

Thanks

do a search for acoustic insulation on ebay...both are available

From a few weeks ago after I posted some room response data, Terry commented:

Hi db,

I'd say that your reverberations times in the octave bands 125 Hz and 250 Hz are a bit too high relative to the higher frequency octave bands. These higher frequency octave band reverberation times are not too low on an absolute scale, but too low on a scale relative to the 125 Hz and 250 Hz octave bands. This unevenness can make the room sound too dead. As for the 63 Hz octave band, reverberation time measurement at these low frequencies is too unreliable in small rooms to be useful.

But since your upper frequencies are fine, you just need more absorption at the highly treatable 125 Hz and 250 Hz octave bands. I recommend either DIY bass traps, as described in this forum and on http://forum.studiotips.com/viewtopic.php?t=535, or ready-made bass traps by forum members RealTraps or GIK Acoustics.

Regards,
Terry

I have since then doubled the sidewall linacoustic to 2" in hopes of absorbing some lower frequencies without further absorbing the higher frequencies. I also treated the ceiling first reflection point.

Data is below:

First, measurements of impulse response in the room with 1" sidewall linacoustic and no ceiling treatement:

http://idisk.mac.com/dbbarron1-Public/Theater/one inch impulse.jpg

Second, with ceiling (first reflection point) and 2" sidewall treatement

http://idisk.mac.com/dbbarron1-Public/Theater/two inch impulse.jpg

Now RT60: Red is no treatment, green is with one inch sidewall treatment and yellow is with two inch treatment. These are 1 octave averages, with 1/3 octave averaging the 2" graph is lower than the 1" as expected except for one errant point which sets off the 1 octave average.

http://idisk.mac.com/dbbarron1-Public/Theater/rt60 comparison.jpg

Lastly, waterfalls; first no treatment

http://idisk.mac.com/dbbarron1-Public/Theater/no treat waterfall.jpg

Second, with 1" sidewall treatement

http://idisk.mac.com/dbbarron1-Public/Theater/one inch waterfall.jpg

Third with 2" sidewall treatment

http://idisk.mac.com/dbbarron1-Public/Theater/two inch waterfall.jpg

I think, to Terry's point, I have addressed the 125-250hz region and ceiling reflection as (separately) suggested. The sound is good, but subjectively, now a bit thin in the mid bass. Will have to think about this a bit.

The big question....am I there yet?

Comments welcome..

db

db, Im about to do the same measurements. Its that REW that does all that?

I have carpet installed, my 4 berkliners and audio setup to do measurements before treatments and after.

pepar, ethan thanks for the explanation.

I am considering the rockwool as people say that it is cheaper than the OC703. Also I can get the rockwool panels in 4'' thickness where as the 703 only comes in 1 or 2'' thickness.

Now my question is whether I should get the rockboard or the RHT.
I guess the rockboard is rigid where as the RHT is semi rigid. I may not cut them into triangles. I am going to just place the panels at the corner and sides. If that is promising then I will take the trouble of cutting.

Also I prefer to order either the rockwool or OC703 online instead of hunting down a local dealer, arranging for a transport etc. Is there a reliable online place for either of these? One of my coworkers has already done a lot of search and I dont think he found an online place.

Thanks
A local "dealer" would actually be an HVAC insulation distributor such as SPI (http://www.spi-co.com/servicecenterdirectory.cfm). Any online source you find will likely be selling the stuff as home theater acoustical absorption instead of HVAC insulation for commercial construction projects. Think about that and the impact on pricing. Also, you will probably find out quickly that, due to the volume (size), shipping costs are high.

Just my $.02.

db, Im about to do the same measurements. Its that REW that does all that?

I have carpet installed, my 4 berkliners and audio setup to do measurements before treatments and after.

Yes - all with REW, a behringer measurement mic and a small mixer to provide phantom power. About a $125 setup additional to the PC.

Also I prefer to order either the rockwool or OC703 online instead of hunting down a local dealer, arranging for a transport etc. Is there a reliable online place for either of these? One of my coworkers has already done a lot of search and I dont think he found an online place.


I bought my OC703 from ebay (best price I could find for 12 1" sheets)

I bought ULTRA touch cotton fibre from soundaway.com .....CHECK THIS STUFF OUT!!! Great for corner bass chunks and its not fibreglass or rockwool, nicer to work with.

I bought rockwool 60 from ATSAcoustics.com

I could have bought some DUCT LINER that works the same way as above from my local HVAC supplier but I already ordered the stuff online. The stuff was from CertainTeed Corp and its also perfect for sound absorption. Call your local HVAC company first BUT DO NOT ask for acoustical liner, instead just ask about duct liner....products with Acoustical in them have a premium price tag!!

Yes - all with REW, a behringer measurement mic and a small mixer to provide phantom power. About a $125 setup additional to the PC.

I have REW, a RS digital SPL meter and a PC. I dont have a clue about the small mixer to provide phantom power. I have used REW before to test my sub but never did waterfall stuff. I guess its time to read the REW FAQ on hometheatershack.com and get it working this weekend again.

Question on RT 60, how low it too low to go?

In dbbarron's post above, there's this graph:

http://idisk.mac.com/dbbarron1-Public/Theater/rt60%20comparison.jpg

I've heard that you want to hit about .3 seconds, and he closes in on .2 for most of the range. Is .2 too dead? Is this a matter of personal taste?

I bought ULTRA touch cotton fibre from soundaway.com .....CHECK THIS STUFF OUT!!! Great for corner bass chunks and its not fibreglass or rockwool, nicer to work with.


I'm very intrigued by this product, it seems when making superchunk bass traps and absorption behind a fabric wall (not rigid enough to frame in panels?), this is a fairly attractive solution.

This is what I see...

Pros:
Non irritating
"Green"
Great acoustical performance, especially in the lower frequencies.
Comparatively priced compared to OC703 (For $120 shipped, I got 96 sq.ft. of 2" 703, $180 shipped for 126 sq.ft. of 3.5" cotton)

Cons:
not rigid enough to frame in panels?
hard to stack into super chunks?

Can you tell us about your experiences working with this material. Is it easy to frame? Will it stack into superchunks and not sag and tip over? Anything in the list that I'm missing?

I'm very intrigued by this product, it seems when making superchunk bass traps and absorption behind a fabric wall (not rigid enough to frame in panels?), this is a fairly attractive solution.

This is what I see...

Pros:
Non irritating
"Green"
Great acoustical performance, especially in the lower frequencies.
Comparatively priced compared to OC703 (For $120 shipped, I got 96 sq.ft. of 2" 703, $180 shipped for 126 sq.ft. of 3.5" cotton)

Cons:
not rigid enough to frame in panels?
hard to stack into super chunks?

Can you tell us about your experiences working with this material. Is it easy to frame? Will it stack into superchunks and not sag and tip over? Anything in the list that I'm missing?

Hi eugovector,

I was interested in this product also and contacted them. They have two products, regular wall insulation and Acoustic Cotton Panels:

http://www.soundaway.com/acoustic_cotton_panels_s/91.htm

These are pretty ridgid and will hold up if cut for bass traps in corners. As for panel mounting without sagging, this is one of the emails sent to me (I too wanted to us them for panels an not to use fiberglass):

Here is the approximate weight per panel:


1" thick x 2' x 4' = 2 lbs.
2" thick x 2' x 4' = 4 lbs.
4" thick x 2' x 4' = 8 lbs.


It is recommended to mount them with a spray adhesive that bonds quickly and a long-term adhesive that will secure on a long-term basis. The spray adhesive is sprayed across the back of the panel while the second adhesive is applied in a bead around the perimeter and across the diagonal of the opposite corners. They will not sag if you use both adhesives.


The spray adhesive covers 64 square feet per can and is priced at $9.95 each. The long-term adhesive, Acoustic-Bond Adhesive, covers 80 lineal feet at 1/4" bead and is priced at $9.95 also. Plan on using 1 can of Acoustic-Bond Adhesive per 4 panels (2' x 4' per panel).


Alex
alex@SoundAway.com

760-599-3985
760-599-4508 (Fax)
Visit us at www.SoundAway.com

I also asked them about material sloughing off and this is their response:

One of the key benefits of using UltraQuiet Acoustic Cotton Panels is being able to hang them without a fabric finish. The panels are made from tightly compressed cotton fibers and do not shed nor release anything into the air. You may, for aesthetic reasons, choose to cover them with GOM fabric that we carry.

Attached you'll find the sound absorbency performance for the panels along with their respective NRC rating.

Call me if you need further assistance.

I look forward to hearing from you.

Alex
alex@SoundAway.com

With the last email they sent me a PDF of the NRC's of their ascoustic cotton pannels. They look pretty good. Contact them, they are very helpful. I'm still deciding what I need for my room.

Ray

With the last email they sent me a PDF of the NRC's of their ascoustic cotton pannels. They look pretty good. Contact them, they are very helpful. I'm still deciding what I need for my room.

I have order the 3.5" utratouch from soundaway.com, 230 sq ft of it, Shipping is a little pricey at $60 but overall the price is similar too OC703 or Rockwool 60. It was easy to order and shipment came pretty fast!

The only thing cheaper is to order duct liner from local HVACs because its closer to $1/sq ft because you can pick it up...its the shipping that is increasing the prices by 50%.

As for the NRCs, ALL of them are on Bob Golds website link that is constantly referred to here....

http://www.bobgolds.com/AbsorptionCoefficients.htm

I have order the 3.5" utratouch from soundaway.com, 230 sq ft of it, Shipping is a little pricey at $60 but overall the price is similar too OC703 or Rockwool 60. It was easy to order and shipment came pretty fast!

The only thing cheaper is to order duct liner from local HVACs because its closer to $1/sq ft because you can pick it up...its the shipping that is increasing the prices by 50%.

As for the NRCs, ALL of them are on Bob Golds website link that is constantly referred to here....

http://www.bobgolds.com/AbsorptionCoefficients.htm

Thanks penngray,

I didn't realize that. I try to keep up with some of the forums, but with a 20month old, I'm pretty busy with other things. Great and informative forum by the way!!! Thanks for all the info.

Here are some comparisons of the ultratouch....

OC703, 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
Rockwool RXL 40 4" (100mm) 4.0 pcf (64 kg/m3) 1.03 1.07 1.12 1.04 1.07 1.08 1.10
Ultra Touch R-13 3.5" (mm) A 0.95 1.30 1.19 1.08 1.02 1.00 1.15


From this I think Ultra touch is the best $$$ choice....to get 4" OC you have to buy more!!

but with a 20month old, I'm pretty busy with other things


lol, I have a 17 month old girl...but I work out my house and she is in bed at 7:30 pm so lots of time to waste on here :D

btw, Im building my corner bass traps this weekend...I have 7 big boxes of acoustical material waiting in my garage to get this stuff done but Im holding off on doing it until I run all the numbers before treatment so I can have a baseline for results.

With the last email they sent me a PDF of the NRC's of their ascoustic cotton pannels. They look pretty good. Contact them, they are very helpful. I'm still deciding what I need for my room.

Ray

Can you post or link the NRC measurements of the panels? Thanks Ray.

Aesthetically, they actually look pretty good. And if they supposedly hold up over time, and their measurements are good, that the lowest price you can find on a finished panel (even my DIY 2" OC 703 panels cost me about $25 each, not counting man-hours). A great deal for those looking to dip their toes into room treatment.

Can you post or link the NRC measurements of the panels? Thanks Ray.

I did above....

Question on RT 60, how low it too low to go?

In dbbarron's post above, there's this graph:

http://idisk.mac.com/dbbarron1-Public/Theater/rt60%20comparison.jpg

I've heard that you want to hit about .3 seconds, and he closes in on .2 for most of the range. Is .2 too dead? Is this a matter of personal taste?

My worries also, but I understand for multichannel surround .2 is an acceptable target. .3 is for two channel (stereo).

To my previous comments, subjectively it is a bit neutral/analytical for stereo listening (actually I am listening in mono during testing)

db

I did above....

I think those are for the flexible rolls, not the rigid panels.

I bought my OC703 from ebay (best price I could find for 12 1" sheets)

I bought ULTRA touch cotton fibre from soundaway.com .....CHECK THIS STUFF OUT!!! Great for corner bass chunks and its not fibreglass or rockwool, nicer to work with.

I bought rockwool 60 from ATSAcoustics.com

I could have bought some DUCT LINER that works the same way as above from my local HVAC supplier but I already ordered the stuff online. The stuff was from CertainTeed Corp and its also perfect for sound absorption. Call your local HVAC company first BUT DO NOT ask for acoustical liner, instead just ask about duct liner....products with Acoustical in them have a premium price tag!!
What was the cost for shipping your purchases?

Can you post or link the NRC measurements of the panels? Thanks Ray.

Aesthetically, they actually look pretty good. And if they supposedly hold up over time, and their measurements are good, that the lowest price you can find on a finished panel (even my DIY 2" OC 703 panels cost me about $25 each, not counting man-hours). A great deal for those looking to dip their toes into room treatment.

eugovector,

Penngray already gave the best link for NRC's for multiple materials. I checked it out, it's incredible and very informative (thanks penngray!). This is what I received from SoundAway:

SoundAway
UltraQuiet Panels
NRC Table
Frequency (Hz) 1" 2" 4"
125 0.08 0.35 0.95
250 0.31 0.94 1.30
500 0.79 1.32 1.19
1000 1.01 1.22 1.08
2000 1.00 1.06 1.02
4000 0.99 1.03 1.00
NRC 0.80 1.15 1.15

I am looking at both the 2" (for reflections), and 4" for bass traps. The finish does already look good, but I may need to still cover with GOM for the WAF.

penngray,
It must be nice to be able to work at home - you get to spend much more time with your kid (except when you're working). I work 10hour days, so have to spend as much time with my son afterwards, then get other things done around the house when he's asleep (at 8pm). I've been thinking of finding work that will allow me to do that also! Thanks for sharring all your info - read some of your other posts/threads. This is a great hobby!!!

I have REW, a RS digital SPL meter and a PC. I dont have a clue about the small mixer to provide phantom power. I have used REW before to test my sub but never did waterfall stuff. I guess its time to read the REW FAQ on hometheatershack.com and get it working this weekend again.
While the RS meter *can* be used as a mic, it is nearly worthless. You would need to buy a suitable mic to get acceptable results with REW. Many use a Beringer mic. The phantom power reference is in re to some mics needing power to operate and that power is supplied over the signal cable . . remotely . . invisibly . . from either a phantom power supply or, in the case of the poster you quoted, a mixer with builtin phantom power.

eugovector,

Penngray already gave the best link for NRC's for multiple materials. I checked it out, it's incredible and very informative (thanks penngray!). This is what I received from SoundAway:

SoundAway
UltraQuiet Panels
NRC Table
Frequency (Hz) 1" 2" 4"
125 0.08 0.35 0.95
250 0.31 0.94 1.30
500 0.79 1.32 1.19
1000 1.01 1.22 1.08
2000 1.00 1.06 1.02
4000 0.99 1.03 1.00
NRC 0.80 1.15 1.15

I am looking at both the 2" (for reflections), and 4" for bass traps. The finish does already look good, but I may need to still cover with GOM for the WAF.



Yes, Bob Gold's is very informative, but I didn't see the measurements for the panels on there, and didn't know how much the response was affected by making the cotton "rigid". If you have the original PDF, perhaps you could forward it to Bob to add to his site.

Strangely enough, the number quoted for the 4" panels are exactly the same as the 3.5" rolls. To the 2nd decimal point, a coincidence?

Still, except in the lowest frequencies, the 2" panels are outperforming OC703. If you're okay with the look, or willing to spend a little more to custom cover them, it would seem to be a great fiberglass alternative.

Still, except in the lowest frequencies, the 2" panels are outperforming OC703. If you're okay with the look, or willing to spend a little more to custom cover them, it would seem to be a great fiberglass alternative.


Im not sure I understand, you cover all of these products no matter what so they all need custom cover?? In the end they all look the same wont they?

Rolls or panels, does it really matter? You can roll it on a wall and it will stick with 3M adhesive spray, then you just cover over it with GOM.

What was the cost for shipping your purchases?

$60 to ship the ultra cotton rolls (8 strips 24"x94"), $30 to ship 12 1" OC703 panels.

While the RS meter *can* be used as a mic, it is nearly worthless. You would need to buy a suitable mic to get acceptable results with REW. Many use a Beringer mic. The phantom power reference is in re to some mics needing power to operate and that power is supplied over the signal cable . . remotely . . invisibly . . from either a phantom power supply or, in the case of the poster you quoted, a mixer with builtin phantom power.


bummer....more money to spend :( I will have to figure out what to buy now and in a hurry because I wanted to start testing this weekend :(

Im not sure I understand, you cover all of these products no matter what so they all need custom cover?? In the end they all look the same wont they?

Rolls or panels, does it really matter? You can roll it on a wall and it will stick with 3M adhesive spray, then you just cover over it with GOM.

penngray,

The cotton rolls are actually made for insulation, not attractive. But the cotton panels:

http://www.soundaway.com/acoustic_co...anels_s/91.htm

Are actually quit attactive already, which is why they already come in colors. They are much stiffer than the rolls (denser) and when mounted with adhesive, may be left as-is without GOM (which I what I may do if my wife accepts the color/look). The pannels have a finished cloth look already, take a look at them.

Also, I'm very sensitive to fiberglass (even if I don't do the install and some fibers leak through the fabric) which is why I was looking for an alternative. The cotton panels are also 'green', made from excess material from making jeans and other clothing, so is more environmentally friendly (something important to me).

As far as covering up, you're right. The material won't matter as far as looks if being covered up.

Thanks!

$60 to ship the ultra cotton rolls (8 strips 24"x94"), $30 to ship 12 1" OC703 panels.



bummer....more money to spend :( I will have to figure out what to buy now and in a hurry because I wanted to start testing this weekend :(

Here is a fairly good mic (I use this one) for REW:

Behringer ECM8000 Measurement Microphone

http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=248-625
around $50

Very flat respone, here are the specs:
Precise electret condenser measurement microphone
Ultra-linear 15 Hz to 20 kHz frequency response
Well-balanced, true omni-directional pattern
Phantom powered, +15V to +48V
Microphone stand adaptor and windscreen for outdoor measurement included

You will need phantom power to operate. You can use the same brand:
Behringer XENYX 802 Mixer 8-Input 2-Bus
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=248-576

Or some other (I'm using one from Tascam).

Are actually quit attactive already, which is why they already come in colors. They are much stiffer than the rolls (denser) and when mounted with adhesive, may be left as-is without GOM (which I what I may do if my wife accepts the color/look). The pannels have a finished cloth look already, take a look at them.

ah, I understand now....:D

btw, thanks for the links for the mic and phantom power. I guess I will need cables too :( I have a Notebook with a USB soundcard that I used with my RS SPL meter now I dont have a clue what to hook up.

ah, I understand now....:D

btw, thanks for the links for the mic and phantom power. I guess I will need cables too :( I have a Notebook with a USB soundcard that I used with my RS SPL meter now I dont have a clue what to hook up.

Yes, you will need a cable (XLR) to connect the mic to the mixer. Instead of the mixer, you can get a computer interface that already has phantom power onboard and a USB out connection for connection to the computer. This costs a bit more (but you need some type of interface anyway). I use:

TASCAM US-144 USB 2.0 4X4 Audio MIDI Computer Interface, about $150

http://www.musiciansfriend.com/product/Tascam-US144-USB2.0-4X4-Audio-Midi-Computer-Interface?sku=242193

If you want a cheaper route, you can use the original mixer with phantom power I mentioned above and purchase a separate interface:

Behringer U-CONTROL UCA202 USB-Audio Interface (about $30)
http://www.musiciansfriend.com/product/Behringer-UCONTROL-UCA202-USBAudio-Interface?sku=702540

There will be more connections with this option.

btw, this site also sells the mic I mentioned (including all the mixers with phantom power), a great site for any recording gear:
http://www.musiciansfriend.com/product/Behringer-ECM8000-Microphone?sku=270400

btw, penngray, it is the "electret condenser" design of the aforementioned microphone that needs powered. that design has two charged "plates" in close proximity to each other that produce a signal when vibrating in relation to each other. the charge is maintained by the phantom power.

You don't need to buy a mixer to get phantom power. Behringer has a "standalone" model for $20 here (http://www.musiciansfriend.com/product/Behringer-MICROPOWER-PS400-Phantom-Power-Supply?sku=336830&src=3WFRWXX&ZYXSEM=0&CAWELAID=26023194). But cavchameleon's USB thingy might kill two birds with one stone.

You don't need to buy a mixer to get phantom power. Behringer has a "standalone" model for $20 here (http://www.musiciansfriend.com/product/Behringer-MICROPOWER-PS400-Phantom-Power-Supply?sku=336830&src=3WFRWXX&ZYXSEM=0&CAWELAID=26023194). But cavchameleon's USB thingy might kill two birds with one stone.

Acutally, that's a much cheaper option, paired with:
Behringer U-CONTROL UCA202 USB-Audio Interface

The total cost is only $50, not bad! With the mic, a total of $100!

Thanks pepar, I didn't know they had a standalone (I'm used to using large mixer that handle >10 mics at once).

I find the mixer quite valuable for level adjustments of inputs/outputs of the soundcard and other purposes, for the extra $25 or so, well worth it IMHO.db.

Agreed! Forgot to mention that.

I find the mixer quite valuable for level adjustments of inputs/outputs of the soundcard and other purposes, for the extra $25 or so, well worth it IMHO.db.
Soundcards (and the O/S) have control panel/mixer software to do that.

I don't think "or" is the right question. Drywall and then treat.

First my Thanks to Terry/Ethan/Pepar on their inputs to my earlier questions.

Actually your responses lead me to seek just a bit more advice on the treatment of my back wall. First a few measurements:

- My screen to back wall distance is 18.5'

- My primary front row seating will be 11' from the screen and 7.5' away from the back wall

- My second row seating will only be 2~3' from the back wall.

Reducing reflections off the back wall seems to be something I need to take seriously - I need to get considerable absorption on or built into that back wall. I am limited in how much "thickness" I can add.

Does anyone know if it would be wise (in other words-safe) to entirely skip the drywalled surface and do the following instead?

1) fill between the 2x4 studs with mineral wool
2) Then cover with 1~2" of linacoustic
3) topped off by an appropriate "wife-approved" GOM covering

Again; I am looking to skip the drywall on the theater side of the wall, and use the full wall depth for additional absortion material? (I do aplogize if this a redundant question in this string).

Thanks Again!
Craig

Here are some comparisons of the ultratouch....

OC703, 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
Rockwool RXL 40 4" (100mm) 4.0 pcf (64 kg/m3) 1.03 1.07 1.12 1.04 1.07 1.08 1.10
Ultra Touch R-13 3.5" (mm) A 0.95 1.30 1.19 1.08 1.02 1.00 1.15


From this I think Ultra touch is the best $$$ choice....to get 4" OC you have to buy more!!

I was planning on building my superchunk bass traps w/in the next couple weeks, but now I guess I'll wait to hear how the superchunks made from this stuff work out. I'd much rather use something like this over fiberglass.

okay, so Im confused today...

to get measurements of the acoustics in my room I need the following...

Notebook - Own it
REW softare - Have it

Measurement Condenser Microphone -Nady CM100 Reference Measurement Condenser Microphone ?? its cheaper on musicians friend and the Berhinger one is backordered.

Phantom Power Supply - Behringer MICROPOWER PS400 Phantom Power Supply (will it work with the nady mic, I assume it will?

Behringer U-CONTROL UCA202 USB-Audio Interface - this is so I can connect it all to my notebook. WAIT, I have a USB audio device like this from SoundBlaster, wouldnt that work?

Musician friend will ship free if Im over $99....and this stuff does it with a cable or two.

I was planning on building my superchunk bass traps w/in the next couple weeks, but now I guess I'll wait to hear how the superchunks made from this stuff work out. I'd much rather use something like this over fiberglass.

If I can get the measurements done pre bass chunks I can put the chunks in and measure again. Now I have to wait for the equipment so it will be next weekend :( I know I need bass chunks no matter what Im just being silly about the pre-treatment measurements because I just want to see the charts before hand.

I dont think there is a question that they utratouch cotton will work. The NRC numbers says it will so I dont doubt it for one minute. If I actually knew about the stuff before I bought the OC703 and rockwool I would have just purchased a large amount the ultratouch stuff. I HATE FIBREGLASS :eek:

okay, so Im confused today...

to get measurements of the acoustics in my room I need the following...

Notebook - Own it
REW softare - Have it

Measurement Condenser Microphone -Nady CM100 Reference Measurement Condenser Microphone ?? its cheaper on musicians friend and the Berhinger one is backordered.

Phantom Power Supply - Behringer MICROPOWER PS400 Phantom Power Supply (will it work with the nady mic, I assume it will?

Behringer U-CONTROL UCA202 USB-Audio Interface - this is so I can connect it all to my notebook.

Musician friend will ship free if Im over $99....and this stuff does it with a cable or two.
you might want to verify that the nady has an individual calibration file with it. no mic is perfectly flat, but if it has been measured and a corresponding file generated then REW will take the mic's output, applies whatever correction is needed to achieve flat and badda bing!

Reducing reflections off the back wall seems to be something I need to take seriously

Yes.

if it would be wise (in other words-safe) to entirely skip the drywalled surface and do the following instead?

Yes, that will be excellent acoustically.

--Ethan

Again; I am looking to skip the drywall on the theater side of the wall, and use the full wall depth for additional absortion material? (I do aplogize if this a redundant question in this string).
Craig, the only suggestion I have is to check and see if any fire or building codes impact your plan.

Hey guys, thanks for the help with my previous questions. I have another to ask...

I'm worried about sound escaping through my window and disturbing my neighbor, whose window is 16 ft. directly across from my window. I'm looking to build a soundproof window plug that doubles as an acoustic panel for my back wall. Here is what i plan to make:

1/2" MDF - Green Glue - 1/2" MDF - 4" OC703

I plan on having the 4" OC703 protrude from the wall while the 1" of MDF fits snugly in the window lined with weatherstripping. This leaves about a 2" airspace between the window and the plug. Would this be effective with regards to soundproofing? Are there any additions I can make that would improve performance? Thanks in advance for the help.

penngray,

The cotton rolls are actually made for insulation, not attractive. But the cotton panels:

http://www.soundaway.com/acoustic_co...anels_s/91.htm

Are actually quit attactive already, which is why they already come in colors. They are much stiffer than the rolls (denser) and when mounted with adhesive, may be left as-is without GOM (which I what I may do if my wife accepts the color/look). The pannels have a finished cloth look already, take a look at them.


Yes, and the panels should be dense enough to just hang on a wall, not have to use adhesive. They say they can be used as ceiling tiles, so they should be able to hang just fine.

Thanks Ethan!

Now all i have to do is make sure I'm not getting sideways with a safety code somewhere.

Regards,
Craig

Craig,

Yes, definitely check with your local building code department. Once a space is finished and therefore considered "habitable," code generally requires drywall to cover all the wall studs. Plus you should know that you are giving up any possibility of good sound isolation for the room. :(

Regards,
Terry

Thanks Terry!

Safety and inspections will be key for me.

As for sound control - Good point. However; this is a bit of an open floor plan and this particular wall defines an adjoining room that is unlikely to be in use when the theater is being used.

penngray,

The cotton rolls are actually made for insulation, not attractive. But the cotton panels:

http://www.soundaway.com/acoustic_co...anels_s/91.htm

Are actually quit attactive already, which is why they already come in colors. They are much stiffer than the rolls (denser) and when mounted with adhesive, may be left as-is without GOM (which I what I may do if my wife accepts the color/look). The pannels have a finished cloth look already, take a look at them.

Also, I'm very sensitive to fiberglass (even if I don't do the install and some fibers leak through the fabric) which is why I was looking for an alternative. The cotton panels are also 'green', made from excess material from making jeans and other clothing, so is more environmentally friendly (something important to me).

As far as covering up, you're right. The material won't matter as far as looks if being covered up.

Thanks!

FYI - the 3lb density cotton shown there can be had for considerably less cost.

Bryan

FYI - the 3lb density cotton shown there can be had for considerably less cost.

Bryan

This is something dense enough that could be used as a panel or ceiling tile, like this (http://www.soundaway.com/acoustic_cotton_panels_s/91.htm), or this is the flexible stuff (http://www.soundaway.com/Ultratouch_Insulation_s/79.htm) that must be glued to the wall, or framed in some way?

Do the performance numbers match up with Sound Away's numbers?

Freq - 2" Panels - 3.5 rolls
125 - 0.35 - .95
250 - 0.94 - 1.30
500 - 1.32 - 1.19
1000 - 1.22 - 1.08
2000 - 1.06 - 1.02
4000 - 1.03 - 1.00
NRC - 1.15 - 1.15

And could you provide a link (or pm me and I'll link it.)?

FYI - the 3lb density cotton shown there can be had for considerably less cost.

really, could we have a link? Not that it matters to me now, I have more then enough material to use in two HT rooms :eek:

FYI - the 3lb density cotton shown there can be had for considerably less cost.

Bryan

Count me in as another interested in a source.

I have 10 GIK panels in my room (you may recall we talked a couple of times) but I have a few "cavities" that I'd love to stuff with some bulk materials and cotton is more appealing to me for that.

The 3lb density panels you showed above are still floppy somewhat but considerably denser than the UltraTouch. The pieces I was referring to are the 3lb panels.

Bryan

Bump...(Looking to finalize the panels and fabricate).....

From a few weeks ago after I posted some room response data, Terry commented:

Hi db,

I'd say that your reverberations times in the octave bands 125 Hz and 250 Hz are a bit too high relative to the higher frequency octave bands. These higher frequency octave band reverberation times are not too low on an absolute scale, but too low on a scale relative to the 125 Hz and 250 Hz octave bands. This unevenness can make the room sound too dead. As for the 63 Hz octave band, reverberation time measurement at these low frequencies is too unreliable in small rooms to be useful.

But since your upper frequencies are fine, you just need more absorption at the highly treatable 125 Hz and 250 Hz octave bands. I recommend either DIY bass traps, as described in this forum and on http://forum.studiotips.com/viewtopic.php?t=535, or ready-made bass traps by forum members RealTraps or GIK Acoustics.

Regards,
Terry

I have since then doubled the sidewall linacoustic to 2" in hopes of absorbing some lower frequencies without further absorbing the higher frequencies. I also treated the ceiling first reflection point.

Data is below:

First, measurements of impulse response in the room with 1" sidewall linacoustic and no ceiling treatement:

http://idisk.mac.com/dbbarron1-Public/Theater/one inch impulse.jpg

Second, with ceiling (first reflection point) and 2" sidewall treatement

http://idisk.mac.com/dbbarron1-Public/Theater/two inch impulse.jpg

Now RT60: Red is no treatment, green is with one inch sidewall treatment and yellow is with two inch treatment. These are 1 octave averages, with 1/3 octave averaging the 2" graph is lower than the 1" as expected except for one errant point which sets off the 1 octave average.

http://idisk.mac.com/dbbarron1-Public/Theater/rt60 comparison.jpg

Lastly, waterfalls; first no treatment

http://idisk.mac.com/dbbarron1-Public/Theater/no treat waterfall.jpg

Second, with 1" sidewall treatement

http://idisk.mac.com/dbbarron1-Public/Theater/one inch waterfall.jpg

Third with 2" sidewall treatment

http://idisk.mac.com/dbbarron1-Public/Theater/two inch waterfall.jpg

I think, to Terry's point, I have addressed the 125-250hz region and ceiling reflection as (separately) suggested. The sound is good, but subjectively, now a bit thin in the mid bass. Will have to think about this a bit.

The big question....am I there yet?

Comments welcome..

db

The 3lb density panels you showed above are still floppy somewhat but considerably denser than the UltraTouch. The pieces I was referring to are the 3lb panels.

Bryan

Are they more/less floppy than 703?

More. Even the 6lb cotton board isn't as stiff as 703 boards. Not sure how they're saying this will work in ceiling grids. I work with the cotton material all the time and I don't see how that would fly.

Bryan

More. Even the 6lb cotton board isn't as stiff as 703 boards. Not sure how they're saying this will work in ceiling grids. I work with the cotton material all the time and I don't see how that would fly.

Bryan

Very good to know. Thank you.

I have a quick question about sand for those of you who may know.

When building your stage, what type of sand are you guys using to fill it? All
I seem to be able to find locally is play sand (child's sand box).

Dry play sand is the stuff.

- Terry

Im wondering what size and how many acousitc cotton panels I need for 10x12 room. Im sitting in my bed right on the back wall and have listening fatigue quick because of the hollowness of the room. Thanks.

Im wondering what size and how many acousitc cotton panels I need for 10x12 room. Im sitting in my bed right on the back wall and have listening fatigue quick because of the hollowness of the room. Thanks.

It's tough to give a general answer with as little information as we have about your room. Post a layout (I like using "room arranger", google it) and maybe some pictures. Even then it will still be best if you do some tests using Room EQ Wizard or something similar.

well I tried the bass trap using 2'' OC 703.

I stacked up to some 6ft as shown in the picture.
Earlier I had just placed a single 2'' 2x4 panel at the
corner.

I am surprised to see that a stack of 6' wedges didnt
make any difference at all compared to a single 2x4 panel.

Also, either with the stack or a single panel, there was not much
change in the peaks and nulls. I also have 2x4 panel at the other 2 corners
in my room.

I was just wondering if I am doing anything wrong for not seeing
any improvement.

well I tried the bass trap using 2'' OC 703...



Do you have pics of your measurement graphs. There are a number of reasons why you may not be seeing the results you're hoping for:

1) The frequency you're looking to affect is too low.
2) 1 stack is not enough treatment to make a big difference
3) Treatment is in the wrong place

I'm not saying these are the case, I'm just saying that it's a possibility.

Do you have pics of your measurement graphs. There are a number of reasons why you may not be seeing the results you're hoping for:

1) The frequency you're looking to affect is too low.
2) 1 stack is not enough treatment to make a big difference
3) Treatment is in the wrong place
My money's on #2.

FYI I am totally new to acoustic treament. I've skimmed through the thread but have not read in detail - sorry if I bring something up that has been covered.

Quick question... I have some 1.5" deep Canvas "paintings" (movie posters printed on canvas actually - pm me if you want the details) for use in our combination living room / home theater. I ordered the 1.5" deep ones over the shallow ones so that I could have some level of acoustical treatment that was wife approved (the only pure sound treatment thing she has approved is some bass traps from acoustical solutions in the sound suede - still trying to decide how much of those I want to do because money is tight right now). I also have some tapestries which I am thinking of putting wall panels behind.

My question is what would be the best material to stuff these canvas paintings with? (keeping in mind they are only 1.5" deep) Just fiberglass from home depot or should I look at ordering some special materials? (edit to add: These are on the side walls)

fiberglass from home depot won't be dense enough.

Any recommendations of something readily available? (or something inexpensive online)

Right now I am having the trouble that for acoustic treatment stuff the shipping costs as much or more than the items (thats one of the problems with the "wife approved" sound suede from acoustical solutions, the shipping is as much as the treatments!)

Any recommendations of something readily available? (or something inexpensive online)

Right now I am having the trouble that for acoustic treatment stuff the shipping costs as much or more than the items (thats one of the problems with the "wife approved" sound suede from acoustical solutions, the shipping is as much as the treatments!)
The way around that is to source the material locally from an HVAC distributor and make your own treatments.

My money's on #2.


I have 2x4 panels at all other corners in my room and a 6' stack at one corner that is near the sub. I also have put panels at 1st reflection points. I used up all 12 panels that came in the box. I really dont see much improvement in the low end. I have attached the curves. Like I said I see the peaks at the same frequencies as before. They have not changed much at the low end. The peak at 142.5Hz has come down a lot but the sound is still as boomy as before because the rest of the curve is still as bad as before with peaks and nulls.

In fact I got better results with just the BFD (DSP1124P) and no panels.
I was ridiculed at the subwoofer forum for just trying the BFD and not the acoustic treatment.

Right now my sub (Sunfire Junior) can only go up to some 90Hz. It is rated as 22-100Hz but rolls off at 90 or so. So I cant control the peaks over 90 using the BFD. I was planning to try the SVS SB10 as it goes up to 200hz. I can set the cross over at 150 or 180hz on my receiver. But I was ridiculed for even having this idea of setting a high cross over and was asked to try the bass traps. Apparently the bass traps dont seem to be working as miraculously as I expected.

BTW the FR is not in log scale. I guess it doesnt matter for display purposes. I use the REW software which gives in log scale but I dont know how to import 2 measurements into REW. So I just used Excel.

My speakers are Klipsch RB81. Receiver is Yamaha RX-V795a (which has a fixed cross over at 90Hz). DVD player OPPO 980H (mainly for 2ch music).
I do have the Onkyo 705 but I really dont see any improvement in sound with the onkyo. Infact my 7 yr old Yamaha RX-V795 sounds better than the Onkyo. Anyway... that is a different story.

just ignore the tall black frames. That is something I had built for my
HT and it is not part of the room treatment.

I have 2x4 panels at all other corners in my room and a 6' stack at one corner that is near the sub. I also have put panels at 1st reflection points. I used up all 12 panels that came in the box. I really dont see much improvement in the low end. I have attached the curves. Like I said I see the peaks at the same frequencies as before. They have not changed much at the low end. The peak at 142.5Hz has come down a lot but the sound is still as boomy as before because the rest of the curve is still as bad as before with peaks and nulls.

In fact I got better results with just the BFD (DSP1124P) and no panels.
I was ridiculed at the subwoofer forum for just trying the BFD and not the acoustic treatment.

Right now my sub (Sunfire Junior) can only go up to some 90Hz. It is rated as 22-100Hz but rolls off at 90 or so. So I cant control the peaks over 90 using the BFD. I was planning to try the SVS SB10 as it goes up to 200hz. I can set the cross over at 150 or 180hz on my receiver. But I was ridiculed for even having this idea of setting a high cross over and was asked to try the bass traps. Apparently the bass traps dont seem to be working as miraculously as I expected.
Focusing only on the corner treatments - very little bass absorption takes place with your FRP panels - single 2x4 panels across the corners are nowhere near enough. Floor-to-ceiling 2x4 panels mounted like this would be better. And one 6' stack of triangles in one corner is, likewise, not enough. The fully filled triangle corner trap style goes deeper than 2" thick panels crosswise (with space behind them; try two corners with that style floor to ceiling. Check the link in my sig for an idea of where you need to head to get results. They should not have dissed you, but bass traps are definitely the way to go. Electronic correction corrects - at best - for one listening position whereas traps improve everywhere. Electronic correction can only be used to reduce peaks. Room nulls cannot be EQ'd out. Bass traps reduce the peaks and the nulls.

Post info on your room size and shape, too.

In fact I got better results with just the BFD (DSP1124P) and no panels.
I was ridiculed at the subwoofer forum for just trying the BFD and not the acoustic treatment.

You have to do both to create the best sub sound, Did you Eq those peaks yet? Honestly, treatment will not do much in solving those peaks and I dont think anyone ever said it would in that thread.

The chunks will reach lower but are no more surface area than a panel straddling. You'll need to do at least the other symmetric corner and try going higher.

Treatment can deal with both frequency and decay time issues. Your waterfalls clearly show improvement in decay time but in the bottom end, it's still just not enough thickness in enough places.

Some of the frequency abberations are likely due to a combination of seating position, speaker position and sub position along with potential mismatch in phase settings from sub to mains.

EQ deals only with the frequency domain and can be used after properly treating a room and setting up the speakers/sub/seating correctly to minimize those issues. You can EQ down the last few stubborn peaks to smooth things a bit. It can also be helpful for VERY low frequencies which are very stubborn to deal with via treatment due to physical size limitations.

Bryan

It can also be helpful for VERY low frequencies which are very stubborn to deal with via treatment due to physical size limitations.


Yes, that was my point above actually, I was only making a point that very low frequencies need EQing no matter what you have in treatment....I have learned that a 25 Hz or 40Hz wavelength is really large and to actually handle that with treatment is physically impossible in many rooms.

The chunks will reach lower but are no more surface area than a panel straddling. You'll need to do at least the other symmetric corner and try going higher.

Treatment can deal with both frequency and decay time issues. Your waterfalls clearly show improvement in decay time but in the bottom end, it's still just not enough thickness in enough places.

Some of the frequency abberations are likely due to a combination of seating position, speaker position and sub position along with potential mismatch in phase settings from sub to mains.

EQ deals only with the frequency domain and can be used after properly treating a room and setting up the speakers/sub/seating correctly to minimize those issues. You can EQ down the last few stubborn peaks to smooth things a bit. It can also be helpful for VERY low frequencies which are very stubborn to deal with via treatment due to physical size limitations.

Bryan


I guess my pictures are misleading. I dont have symmetric corners at the
front. I had a picture of the same corner with a 2x4 panel and a 6' stack.

I will try to fill the stack all the way to the ceiling and also try full height
2x4 panels on the other corners. It was really difficult to cut the panels using that slicer in pepar's page. I bought the same thing.

May be I need to use a thickner wooden piece as pepar did so that the slicer will go all the way through the panel. it took me some 5 hrs or so to make that 6' stack !

You have to do both to create the best sub sound, Did you Eq those peaks yet? Honestly, treatment will not do much in solving those peaks and I dont think anyone ever said it would in that thread.

yep with the BFD (DSP1124P) I was able to EQ the peaks. I tried the FBQ2496 as it is supposed to be better but looks like mine is defective because it lowers the entire output even if I set a genative gain at one frequency. I also verified this using full range signal. Anyway...I will post that in the BFD thread as it is out of topic here.

I guess my pictures are misleading. I dont have symmetric corners at the
front. I had a picture of the same corner with a 2x4 panel and a 6' stack.

I will try to fill the stack all the way to the ceiling and also try full height
2x4 panels on the other corners. It was really difficult to cut the panels using that slicer in pepar's page. I bought the same thing.

May be I need to use a thickner wooden piece as pepar did so that the slicer will go all the way through the panel. it took me some 5 hrs or so to make that 6' stack !
No doubt it is a wrist-killer, but in 5 hours I did about 4x what you did. The knife dulls right away and from then on it's muscling through it. It was good that I use my right wrist regularly. :rolleyes:

Planning on putting up my Linacoustic and GOM this weekend in my 16'x20' theater. I'm planning on putting Linacoustic on the entire front wall and on the bottom half of the rest of the room to just above ear level. The big question I have is: Poly or no poly on the top half of the room?

Photos of the room (http://www.houseofpancake.com/index.php?com=com_photos&action=gallery&id=489&page=2)

Planning on putting up my Linacoustic and GOM this weekend in my 16'x20' theater. I'm planning on putting Linacoustic on the entire front wall and on the bottom half of the rest of the room to just above ear level. The big question I have is: Poly or no poly on the top half of the room?

Photos of the room (http://www.houseofpancake.com/index.php?com=com_photos&action=gallery&id=489&page=2)
Poly?

It is sooo easy to overdeaden small theaters. My walls are walls are painted plaster above the wall carpet. Check the site linked in my sig.

BTW, some nice dust on your camera lens! :D

If I can get the measurements done pre bass chunks I can put the chunks in and measure again. Now I have to wait for the equipment so it will be next weekend :( I know I need bass chunks no matter what Im just being silly about the pre-treatment measurements because I just want to see the charts before hand.

I dont think there is a question that they utratouch cotton will work. The NRC numbers says it will so I dont doubt it for one minute. If I actually knew about the stuff before I bought the OC703 and rockwool I would have just purchased a large amount the ultratouch stuff. I HATE FIBREGLASS :eek:

Hey penngray, any updates on this? I have my front wall mostly treated, now I'm just waiting to do the superchunks.

Hey penngray, any updates on this? I have my front wall mostly treated, now I'm just waiting to do the superchunks.

The pre-treatment measurements are done now and this weekend Im building my bass traps.

The pre-treatment measurements are done now and this weekend Im building my bass traps.
Very anxious to see the before and after measurements!!!

Very anxious to see the before and after measurements!!!

me too!! I did three different Mic placements because they all had different results. My room design isnt perfect and my Subs are "locked" in certain positions so there are limits to my success :D

My whole HT build thread is VERY OUTDATED so I have to update it with lots of pics and charts. I will do so this weekend.

me too!! I did three different Mic placements because they all had different results. My room design isnt perfect and my Subs are "locked" in certain positions so there are limits to my success :D

My whole HT build thread is VERY OUTDATED so I have to update it with lots of pics and charts. I will do so this weekend.

Cool! Looking forward to your results/impressions.

I'm in the middle of getting my REW outfit set up and then I'm ready to work over similar before/after graphs and charts.

Good luck...

me too!! I did three different Mic placements because they all had different results. My room design isnt perfect and my Subs are "locked" in certain positions so there are limits to my success :D
Most are. Mine certainly are. IMO, that's where SSC traps come in, if one is able to incorporate them into one's theater. They are not easy to hide.

Do you know about the upcoming AVS AS-EQ1 (http://www.svsound.com/CES2007/SVS_AudyessyRelease.pdf)?

Do you know about the upcoming AVS AS-EQ1?

Nope, thats a pretty cool product...if its cheap enough I will own it :eek: but I already have the BFD DSP1124p and the eD EQ.2, add to that two velodyn SC-1250s that do EQing....lol. I doubt I need all those!

When running REW to get my room measurements do I only look at Waterfalls up to around 1K Hz? then beyond that use RT60?

Nope, thats a pretty cool product...if its cheap enough I will own it :eek: but I already have the BFD DSP1124p and the eD EQ.2, add to that two velodyn SC-1250s that do EQing....lol. I doubt I need all those!
Projected at $750. What it does differently than what must now be called "conventional" electronic correction (EQ) is set filters in both the frequency domain and the time domain. Plus, this unit "does" two separate and independent sub channels. It phases them, sets the levels and then applies the Audyssey filters I mentioned. Even if you could EQ two separate sub channels, the time domain stuff is new and proprietary. If your BFD is playing checkers, Audyssey-powered units (AVRs and pre/pro, and now this) are playing chess . . 3D chess.

- Jeff

When running REW to get my room measurements do I only look at Waterfalls up to around 1K Hz? then beyond that use RT60?
The waterfalls are a visualization of decay. RT60 is easy to determine from a waterfall; simply look at the time it takes for the level to drop 60 dB.

Any information on Tube traps ???

http://www.acousticsciences.com/pricing.htm

It seems this is the only way to really control the sub 80Hz frequencies. Im planning on building triangle corner traps but if they are not as effect as tube traps then maybe I should build tube traps.

Any information on Tube traps ???

http://www.acousticsciences.com/pricing.htm

It seems this is the only way to really control the sub 80Hz frequencies. Im planning on building triangle corner traps but if they are not as effect as tube traps then maybe I should build tube traps.
What is the first column - the frequency? Do they go to that or are they tuned to that? If the latter, then they are not broadband like SuperChunk traps.

Any information on Tube traps ???

http://www.acousticsciences.com/pricing.htm

It seems this is the only way to really control the sub 80Hz frequencies. Im planning on building triangle corner traps but if they are not as effect as tube traps then maybe I should build tube traps.
This is a price list. It can say anything. The manufacturer can claim anything. Ask them for the complete ASTM C-423 lab reports on these products. These are the standardized, independent tests for sound absorption over a wide range of frequencies. If these cannot be furnished, I would not even consider buying the product.

Regards,
Terry

Terry, just to be clear, ASC is a respected (by me) company who has been around for a long time, and their products do work. Maybe not the skinny little tubes and quarter-rounds, but their large and expensive 20-inch full-round model definitely works. Bang for the buck is a different issue, but the performance is there on the largest model.

--Ethan

Terry, just to be clear, ASC is a respected (by me) company who has been around for a long time, and their products do work. Maybe not the skinny little tubes and quarter-rounds, but their large and expensive 20-inch full-round model definitely works. Bang for the buck is a different issue, but the performance is there on the largest model.

--Ethan
Of course, I know that Ethan. But if they are going to put Hz numbers on their tube traps, the burden of objective proof is on them. They didn't have to give them any specs at all. But since they are, well, ...

Art is a big boy. He should be able to handle such a request.

Regards,
Terry

No lab test results....no buy. A gem of wisdom for an product claiming acoustical (or other magic) properties.

No lab test results....no buy. A gem of wisdom for an product claiming acoustical (or other magic) properties.

+1 on that. Without hard facts, anyone can claim just about anything. Specially at their steep prices, I want scientific proof they do what they claim.

I had used the GIK Tri Traps in my family room, had 4 of them. Do to a change in furniture I had to let them go. I was thinking of using the RPG Modex traps in the top of the corners.

Any thoughts on the RPG Modex Bass Traps?

Thanks

The RPG Modex traps are tuned membrane absorbers. They are fabricated and sold for specific center frequency bands. They are meant to absorb over relatively narrow frequency regions, and are not wide-band like the GIK traps.

You could use multiple Modex traps tuned to cover multiple adjacent frequency bands. RPG purposely varies the tuning within the specific band. But this is very expensive. You'd need many of these costly devices to achieve this.

On the subject of testing, RPG provides absorption data on their bass traps, measured in their own facility by the impedance tube method. But I've never seen any ASTM C-423 reverberation room measurements for Modex absorbers. So we don't actually know how the absorption coefficients, limited to 1.0 by virtue of the impedance tube method, translate into sabins of reverb room absorption!

Regards,
Terry

The RPG Modex traps are tuned membrane absorbers. They are fabricated and sold for specific center frequency bands. They are meant to absorb over relatively narrow frequency regions, and are not wide-band like the GIK traps.

You could use multiple Modex traps tuned to cover multiple adjacent frequency bands. RPG purposely varies the tuning within the specific band. But this is very expensive. You'd need many of these costly devices to achieve this.

On the subject of testing, RPG provides absorption data on their bass traps, measured in their own facility by the impedance tube method. But I've never seen any ASTM C-423 reverberation room measurements for Modex absorbers. So we don't actually know how the absorption coefficients, limited to 1.0 by virtue of the impedance tube method, translate into sabins of reverb room absorption!

Regards,
Terry

Terry,

Thanks, do you know of any bass traps about the size of modex?

Terry,

Thanks, do you know of any bass traps about the size of modex?
Yes. One is the Studiotips SuperChunk:
http://forum.studiotips.com/viewtopic.php?t=535

Another is the Auralex MegaLENRD (not pretty, but effective):
http://www.sweetwater.com/store/detail/LENRD4PUR/

Test data for both are here:
http://forum.studiotips.com/viewtopic.php?t=536

The SuperChunk is a DIY solution, but I would venture a guess that you could get someone on the AVS forum to build and ship a version to you, covered in nice Guilford fabric, for a fraction of the price of the RPG Modex Corners! :)

Regards,
Terry

loose fill cellulose insulation for superchunks.

i am about to insulate my basement. i used a product called insulweb which is glued and stapled to the studs. a 4" slit is made in the insulweb "fabric" as required and a hose inserted into the cavity through which cellulose is blown. unlike loose fill cellulose in attics, the object is to achieve a cellulose density of 3.5lb/cubic foot. this is recommended to insure no settling.

my thought is i could build "nooks" into the corners covered with insulweb and then blow the insulation in. i could later build fabric panels to pretty it up.

does anyone see this as viable? i guess the question is how 3.5lb/cubic foot cellulose compares to the traditional dense fiberglass products normally used.

any ideas guys? if this works, it would likely be the cheapest way to do these as long as you get more than 20-25 bags (lowes lends their blower free is you get a minimum amount).

thanks for your replys!!

Test data for both are here:
http://forum.studiotips.com/viewtopic.php?t=536

Since we're being sticklers for accurate and valid test data, the "data" on that page is not certified and suffers from two big problems:

1) ASTM tests require at least 60 square feet of surface area for reliable results, and those tests had less than one third that. Just because a test is performed in a certified lab does not mean the test is legitimate. :eek:

2) ASTM has no standard for corner mounted traps. They should have this! But they don't. Yet. I'm sure you saw my article in Sound and Vibration magazine addressing the failure of the current test standards, but for the benefit of others who may be interested here's the link:

http://www.realtraps.com/art_testing.htm

BTW, I agree that Art Noxon (ASC head) is a big boy, and I agree with Dennis that data is what separates snake oil from legitimate products. But I didn't want people here who have not heard of ASC to think ASC is suspect. (Yikes, I can't believe I'm supporting the reputation of a direct competitor! But what's fair is fair...)

--Ethan

loose fill cellulose insulation for superchunks.

i am about to insulate my basement. i used a product called insulweb which is glued and stapled to the studs. a 4" slit is made in the insulweb "fabric" as required and a hose inserted into the cavity through which cellulose is blown. unlike loose fill cellulose in attics, the object is to achieve a cellulose density of 3.5lb/cubic foot. this is recommended to insure no settling.

my thought is i could build "nooks" into the corners covered with insulweb and then blow the insulation in. i could later build fabric panels to pretty it up.

does anyone see this as viable? i guess the question is how 3.5lb/cubic foot cellulose compares to the traditional dense fiberglass products normally used.

This density of cellulose has roughly the same acoustic resistivity as OC 705 fiberglass. I would therefore expect it to perform about as well in this application.

Regards,
Terry

I have read through this thread and cannot find an answer to my questions.

1. How do you attach the Linacoustic to the drywall?

2. How do you attach the GoM to the Linacoustic?

~Josh

ok I added 703 to the 3 corners in my room.
I really see no improvement in the peaks/nulls.

May be it sounds a little better than before but
that may be psychological.

To be honest this has been just a waste of time and effort.
I dont care much about the money as I spent just under $200
for the 703 and other supplies. But considering very negligible
impact it had to the curve I feel this has all been just a waste of
time. Sorry I just dont buy the argument that I have to go all the way to the
ceiling. Now I have upto some 7ft at all 3 corners and going another 2 feet is not going to make the curve flat.

I am sure I can make the curve a lot better using the BFD FBQ2496 without any of the 703. Sure it is only for one position. I dont care much about other positions as I am single :-)
So only my seating position matters. I guess I will try the SVS SB12 or SB10 as it can go upto some 200Hz (pretty flat ) and then set the cross over very high and EQ using FBQ2496. Then I dont
have to worry about my mains. Now my sub can go only up to some 90Hz and the rest
of the curve is due to the mains/fronts. In fact the SVS SB12 or SB10 can go up to 300Hz without significant drop. So I could set the cross over at 200hz which I guess is as high as it gets on any AVR.

I will go against convensional wisdom that subs are meant to be under 80Hz. Now I am going my convensional wisdom and it sucks. I dont think it can get any worse. Like I have mentioned in other posts, I can always move the sub to the center if I find it directional when I set the crossover high. Other than becoming directional I really dont see any drawbacks of using a high cross over on the sub.

People just keep arguing but how many people here or in the subwoofer forum have used a sub like SVS SB12 (that can go as high as 200-300Hz ) with a high cross over to see how it sounds before just denouncing it as a bad idea. Now I know that 703 wasnt a good idea so I shall try the other route and see what it has to offer. I can always return the sub as SVS offers a 60-day return.

BTW: just ignore that black frame and the fact that the FR is not in log scale. I made those
black frames for the screen that I had in that recess. I havent found a better place
to move the frames since I moved the screen to the wall where the other corner is.

My new media room is nearing completion. After dong quite a bit of testing and listening (and contrary to most comments here) I have sort of settled on a modified live end - dead end design using DIY panels. Front half of the room is almost totally dead down to about 250hz, and the back half has a bunch of bass traps to attenuate the 250 and below but is quite live above 250HZ. I built the speakers with a matching 250 HZ crossover to the woofers and will eventually tune the port frequency rolloff to match the room response and tidy up any leftovers with a little EQ if required. Yes, a bit tricky. I'm still working on the front wall so the final design is not quite done.

My source is mostly CDs through a Behringer Uultracurve (temporary, I hope) then to a Yamaha DSP3000 (COAX) which does the final D-A for the L&R mains, L&R front surrounds, and L&R rear surrounds. Will not use a center channel with the Yamaha. The Yamaha recommends a "dead" room but I find it a little too creepy, hence the live back end, at least for the higher frequencies. The final consideration is 5.1 decoding by a Sony E800 which is my last can of worms The outputs of Yamaha and the Sony will be switched to the amps. Now I gotta figure what to do about the center channel (already got the speaker built.)

Not mentioned much in all the discussions is how the dead end cuts left-right crosstalk to the listener (up close you even get the headphone effect.) This apparently focuses the mono image in a very surprising way. The speakers are about ten feet apart and the center mono image is distinctly about three to four feet wide and dead center, and solid as a rock. Seating position seems less critical - moving right to left does not seem to change the apparent center much. The mono image seems more natural and in the same plane as the six foot wide projection screen. I am beginning to like this effect, especially for dialog. At first listen it seems more theater like than a dedicated center channel speaker. I and am considering ditching the center channel speaker.

Has anybody observed this in their setup? If so I'd love to know more. Comments? Opinions? Speculations?

I just stacked my Rockwool 60 panels in all corners 12" thick to do a simple test.



No treament waterfall (ignore greater than 300 Hz, I forgot to set the ranges)

http://www.penngray.com/HTRoom/may24_waterfall2.png

Initial simple corner bass treatment

http://www.penngray.com/HTRoom/june1_waterfall.png

Current Sub FR plot

http://www.penngray.com/HTRoom/june1_measure1.png

Some questions, can I really control the sub 80Hz stuff? Do I really care? Its sounding pretty good, I like the huge compression I feel and the fact that I can shake the room with my dual subs :D

Im actually going to install all treatments this week.....FINALLY!!!

ok I added 703 to the 3 corners in my room.
I really see no improvement in the peaks/nulls.

May be it sounds a little better than before but
that may be psychological.

To be honest this has been just a waste of time and effort.
I dont care much about the money as I spent just under $200
for the 703 and other supplies. But considering very negligible
impact it had to the curve I feel this has all been just a waste of
time. Sorry I just dont buy the argument that I have to go all the way to the
ceiling. Now I have upto some 7ft at all 3 corners and going another 2 feet is not going to make the curve flat.

I am sure I can make the curve a lot better using the BFD FBQ2496 without any of the 703. Sure it is only for one position. I dont care much about other positions as I am single :-)
So only my seating position matters. I guess I will try the SVS SB12 or SB10 as it can go upto some 200Hz (pretty flat ) and then set the cross over very high and EQ using FBQ2496. Then I dont
have to worry about my mains. Now my sub can go only up to some 90Hz and the rest
of the curve is due to the mains/fronts. In fact the SVS SB12 or SB10 can go up to 300Hz without significant drop. So I could set the cross over at 200hz which I guess is as high as it gets on any AVR.

I will go against convensional wisdom that subs are meant to be under 80Hz. Now I am going my convensional wisdom and it sucks. I dont think it can get any worse. Like I have mentioned in other posts, I can always move the sub to the center if I find it directional when I set the crossover high. Other than becoming directional I really dont see any drawbacks of using a high cross over on the sub.

People just keep arguing but how many people here or in the subwoofer forum have used a sub like SVS SB12 (that can go as high as 200-300Hz ) with a high cross over to see how it sounds before just denouncing it as a bad idea. Now I know that 703 wasnt a good idea so I shall try the other route and see what it has to offer. I can always return the sub as SVS offers a 60-day return.

BTW: just ignore that black frame and the fact that the FR is not in log scale. I made those
black frames for the screen that I had in that recess. I havent found a better place
to move the frames since I moved the screen to the wall where the other corner is.

here is the before-after FR

Are your before and after reverse labeled? If not, then stick with the before, eh?! :D

Are your before and after reverse labeled? If not, then stick with the before, eh?! :D

nope the labels are correct. "After" is the one with bad nulls.
yep like I said all those effort was just a waste of time.

The only thing 703 could do is probably give me lung cancer!

I guess I am going to pursue the EQ route using the SVS SB12 and FBQ2496

I am going to ask my coworker who is building his HT to come get
all the 703 crap out of my living room before they find their way
into my lungs :-)

BTW: has anyone been concerned that having all that fiber glass stuff in the room is a health hazard? The fibers dont come out or spread unless the panels are rubbed or cut and they are no finer than the dust from the carpets. I dont want to spend several hundread bucks on GOM to cover up all the 703 stuff. I would rather dump them in trash in those plastic bags I got from the place where I bought them.

I dont want to spend several hundread bucks on GOM to cover up all the 703 stuff. I would rather dump them in trash in those plastic bags I got from the place where I bought them.

You have to cover 703 with something, it should never be left exposed.

I used dense 3/4" thick polyester batt (comes in a big roll for upholstery and bedding) over the glass in my panels -- looks like air filter material. It provides a mechanical barrier against disturbing the glass, including air flowing from the AC/heat vents across the surface. Because it has low density compared to glass it probably has very little acoustic effect but it might cut high frequency reflections at shallow angles where glass might be a little reflective. It is white so it will show through dark color fabric. Looks OK under light beige Wallymart burlap.

You have to cover 703 with something, it should never be left exposed.

is it due to health reasons?

Considering the fact that they didnt make a big difference and that it may be a health hazard if left uncovered, I am going to get rid of them. My coworker is not ready with his HT for him to take them. So I am going to just dump them in trash in the plastic bags they came in.

Total 24 2'' panels. 8 of them are still uncut. I might keep 3 to cover the
fire place as it seems to insulate the fire place from cold draft (I dont use the fire place). Only for those 3 I will add some cheap cover.

I live in Detroit metro. If anyone is interested in taking them let me know.
I am not asking for a lot of money. May be $25 to cover the cost to wrap those 4 panels with some cloth/frame.
They are well cut. oh yeah you can take the slicer too. I had of them.
One got very dull so I trashed it. Other one is new and I only cut some 5-6 panels using that.

I may not wait too long. The sooner I get rid of them the lower the risk of getting any health issues. I may even start dumping them in the next couple of days, keeping only 3 penals in the garage. I am not sure if waste management will have any issues if I dump them in my drive way. Will test it first with a few panels :-)

And for those of you trying to put the 703: Good luck and god bless :-)

Considering the fact that they didnt make a big difference and that it may be a health hazard if left uncovered, I am going to get rid of them. My coworker is not ready with his HT for him to take them. So I am going to just dump them in trash in the plastic bags they came in.



Woah, don't trash 'em dude. Someone here will take them. Post them in the classifieds, and I bet you could get some money for them. If I were in the Detroit area, I'd be there in a hot minute.

Woah, don't trash 'em dude. Someone here will take them. Post them in the classifieds, and I bet you could get some money for them. If I were in the Detroit area, I'd be there in a hot minute.

Ya I could use several uncut ones, but I think shipping would be too much to the west coast.

I think the mistake you're making is to concentrate on frequency rather than time.

I've just installed bass absorbers in my two front corners, and whilst my frequency response hasn't changed a great deal, I could immediately hear the benefit of the reduced reverb times (which I haven't measured).

I have absolutely no hesitation in recommending this for others to try.

And if you're worried about the health effects, then re wrap the pieces in thin plastic garbage bags. This has no effect on the frequencies we're trying to absorb.

I think the mistake you're making is to concentrate on frequency rather than time.

I've just installed bass absorbers in my two front corners, and whilst my frequency response hasn't changed a great deal, I could immediately hear the benefit of the reduced reverb times (which I haven't measured).

I have absolutely no hesitation in recommending this for others to try.

And if you're worried about the health effects, then re wrap the pieces in thin plastic garbage bags. This has no effect on the frequencies we're trying to absorb.

yeah you have a point. The FR has not changed but the boominess is not there as much. Earlier the bass guitar sound was just boomy and the boominess use to linger for a while now the boominess is not there as much and also I noticed that the same base guitar sound seems to be shorter in time i.e as if the guy took his finger off from the guitar.

Is this what you are talking about reverb time etc.

How do I make that waterfall plot. I have REW but I dont know how to make the impulse reading and I also dont know how to interpret the waterfall plot.

So are are saying that putting them in plastic bags does not hurt its effectiveness. Some folks in this thread were debating if felt would be acoustically transparent. Well if plastic bag does not hurt then anything would be fine right?. Now is the plastic bag ok only for low frequencies or for both low and high. I have the uncut panels on the side and front walls as absorbers for high frequencies.

I have put in so much effort into this so I dont want them to go waste.

If the health risks are not worse than the fibers from the carpet and if I dont have any vents near the panels, can I just leave them uncovere?

Total 24 2'' panels. 8 of them are still uncut. I might keep 3 to cover the
fire place as it seems to insulate the fire place from cold draft (I dont use the fire place). Only for those 3 I will add some cheap cover.

I live in Detroit metro. If anyone is interested in taking them let me know.
I am not asking for a lot of money. May be $25 to cover the cost to wrap those 4 panels with some cloth/frame.
They are well cut. oh yeah you can take the slicer too. I had of them.
One got very dull so I trashed it. Other one is new and I only cut some 5-6 panels using that.


Sorry you feel that they didnt do much but I posted a long time ago (here and in your thread) that sometimes treatments does very little for problem FR plots. Your treatements I suspect did a great job in the reverb times (as Peter posted above). I think you have other setup and room issues that treatments can not solve.

I think they will still work for you and fabric is cheap over at Jo-ann fabric so get some and cover them up. Anything looks better then OC703 ;) You can put anything over them, more reflective fabric will stop the absorbtion of only high frequences, lower frequencies are still absorbed

Walmart burlap is cheap and for me looks just fine. Coarse weave is good at higher frequencies also. Does not stretch much and requires lots of staples for a smooth appearance. I worry that plastic might buzz up against a fixed surface.

Sorry you feel that they didnt do much but I posted a long time ago (here and in your thread) that sometimes treatments does very little for problem FR plots. Your treatements I suspect did a great job in the reverb times (as Peter posted above). I think you have other setup and room issues that treatments can not solve.

I think they will still work for you and fabric is cheap over at Jo-ann fabric so get some and cover them up. Anything looks better then OC703 ;) You can put anything over them, more reflective fabric will stop the absorbtion of only high frequences, lower frequencies are still absorbed
His traps still fell a few feet short of the ceiling. And, depending on the size of his room, perhaps three wall/wall corners are not enough trap. First, I'd fill them to the ceiling. And being the firm believer in SSC bass traps that I am, I would suggest that the OP consider placing some at ceiling/wall "corners." In my 13x21x8 room, the two front wall/wall corners and the front wall/ceiling corner traps made a HUGE improvement. (See sig)

Just my $.02.

looking for low profile, reasonably attractive ceiling diffusion, preferably in black; anyone have any experience with:


GIK D1 Diffusor http://www.gikacoustics.com/gik_d1_diffusor.html

RPG Hemiffusors http://www.rpginc.com/products/hemiffusor/index.htm

or

Studio Outfitters Roundffusor http://www.studiooutfitters.com/roundffusor.html

or other suggestions?

Has there ever been a definitive answer to how far you need to sit away from a diffuser for it to be effective?

Mupi,

Bass boominess is exactly what we mean by reverb time. According to most measurement standards the reverb time, measured in seconds, is the time it takes the sound level to drop 60dB. It's obviously frequency dependent and so the reverb time can be quoted for any particular frequency or as a graph covering all frequencies. An important design goal is to have similar reverb times at all frequencies, and many designers aim for around 0.35 seconds, in a typical sized home theatre. As room size increases the target reverb time also increases.

It's obviously much harder to tame the reverb time in the lower frequencies, due to the absorber size required, but my experience has certainly made me a believer. I went pretty large with my corner absorbers; the side lengths of the triangles are 24" / 24" / 35".

The facing or wrapping to be used depends entirely on the frequency range you're trying to absorb. For bass traps almost anything is OK. For full range absorbers the open weave fabrics are best.

The main problem with the fibres is not long term health problems, but severe itchiness from them getting into your skin. If this happens the best remedy is to rinse in COLD water.

The main problem with the fibres is not long term health problems, but severe itchiness from them getting into your skin. If this happens the best remedy is to rinse in COLD water.
Warm water opens pores allowing the fibers to penetrate deeper making them harder to remove. Cool/cold water does the opposite.

I went pretty large with my corner absorbers; the side lengths of the triangles are 24" / 24" / 35".


Im going 17"/17"/24" in two corners but I might build a 24"/24"/35" in the one other corner.

Is there a huge difference between those sizes?

Also on my back wall, Im put up that 4" thick treatment suggested a long time ago but Im back wondering if I should leave an 1" air gap between it and the wall?

What does that improve again? Why 4" thick and a 1" air gap, why not 5" thick instead? No doubt, Im constantly confused.

Im going 17"/17"/24" in two corners but I might build a 24"/24"/35" in the one other corner.

Is there a huge difference between those sizes?
Being a DIY and non-commercial solution, testing has been nearly non-existent. The test referenced (http://forum.studiotips.com/viewtopic.php?t=536) at the Studiotips Forum is for the 24" face version. Even behind my false wall, I could not fit that size. So I went with the 24" face. Material costs factored in as well. If you search and find commercial product comparisons to the 24" face, please post.

- Jeff