Acoustical Treatments Master Thread [Text View] - Page 7

Terry Montlick

08-09-06, 02:15 PM

Hi, Terry, will you please expand on that, especially your qualification with different room surface absorptions? And, if possible, perhaps couch it in layman's terms?

:)
Sure!

The notion is that when you have a range of different absorption coefficients on surfaces in a room, the surfaces with less absorption have greater influence on the reverberation time. These "more-live" surfaces make the reverberation time longer -- longer, in fact, than would be predicted by a reverberation time formula such as the Eyring equation. [With a mix of absorption coefficients, some of them being large, the Eyring reverberation time formula should be used instead of the Sabine formula.]

But when you add diffusion, you mix up the wave directions a lot. This causes waves that might otherwise get stuck reflecting only between less absorptive surfaces to hit and be absorbed by surfaces with higher absorption coefficients. The reverberation dies out quicker. The results conform much better with the Eyring equation, which in fact presumes a diffuse sound field. And that's just what diffusion provides.

- Terry

myfipie

08-09-06, 02:24 PM

It's only a tree-day course; they can't go into depth on everything. And, IMO, a more apt analogy is that it's like learning how to build a car, but not telling you how to spin balance the wheels. The car will still run, but it's not "optimized." :)

So would you like to go back and forth and insult each other about this for about 4 pages? :D :D :D :D :D

Glenn

myfipie

08-09-06, 02:26 PM

> We are not told how to BUILD bass traps, we are told to buy them. <

That makes a lot of sense. Of course I'd say that! :D

Seriously, unless someone values their time at $7 per hour, or just loves to get their hands dirty for the fun of it, building bass traps is not usually cost effective. And certainly not for a professional installer doing custom jobs in homes where people care about appearance.

> I'm trying to figure out how to build them. <

It's all right here:

www.ethanwiner.com/acoustics.html

--Ethan

:D :D

CriticalListener

08-09-06, 02:48 PM

pepar

08-09-06, 02:49 PM

So would you like to go back and forth and insult each other about this for about 4 pages? :D :D :D :D :D

Glenn
I have a strict one-page limit on that. :p :D

pepar

08-09-06, 02:55 PM

Sure!

The notion is that when you have a range of different absorption coefficients on surfaces in a room, the surfaces with less absorption have greater influence on the reverberation time. These "more-live" surfaces make the reverberation time longer -- longer, in fact, than would be predicted by a reverberation time formula such as the Eyring equation. [With a mix of absorption coefficients, some of them being large, the Eyring reverberation time formula should be used instead of the Sabine formula.]

But when you add diffusion, you mix up the wave directions a lot. This causes waves that might otherwise get stuck reflecting only between less absorptive surfaces to hit and be absorbed by surfaces with higher absorption coefficients. The reverberation dies out quicker. The results conform much better with the Eyring equation, which in fact presumes a diffuse sound field. And that's just what diffusion provides.

- Terry
Thanks, I see and understand the premise. Is this always the case? Isn't it just as likely that sound that would have been reflected onto an absorptive surface instead is reflected onto a reflective surface?

pepar

08-09-06, 03:00 PM

It seems that, in my area, 705 & 1212 are nearly impossible to find. So I took Ethan's suggestion on his website and found a Knauff FSK board that is 6lbs/foot and ordered that (not a great price $1.71 sq ft) but with nothing else available I took it.

Normally I would buy the bass traps, but I'm having my carpenter build 7' x 2' frames of stained wood that match the other carpentry work in my showroom. I'm going to cover them with my left over 1" Owens Corning Black Acoustic board, and I hope they will come out looking very sharp.
I ordered my 703 from an HVAC insulation distributor. (I could have just as easily ordered 705.) Got my J-M Linacoustic and OC SelectSound Black from them as well. Killer pricing, but I had to pick it up. Got the roll of Linacoustic into the SUV, but had to rent a truck to pick up the 4x8x2 sheets of SelectSound.

Terry Montlick

08-09-06, 03:17 PM

Thanks, I see and understand the premise. Is this always the case? Isn't it just as likely that sound that would have been reflected onto an absorptive surface instead is reflected onto a reflective surface?
Yes, but that reflected sound will soon have more chances to hit the absorptive surfaces. The randomness added by the diffusion provides this.

"Always" is a word I am hesitant to use. In the papers I referred to earlier, the lowering of RT60 with increased absorption was consistently shown. The rooms ranged from simple boxes to complex concert halls. This doesn't mean that one could not come up with an artificial example room which exhibited the reverse.

- Terry

pepar

08-09-06, 03:27 PM

In the papers I referred to earlier, the lowering of RT60 with increased absorption was consistently shown. The rooms ranged from simple boxes to complex concert halls. This doesn't mean that one could not come up with an artificial example room which exhibited the reverse.
You mean "diffusion" there, right?

I'm thinking of adding diffusors - Skyline LPs - to my theater to make it a bit livelier. I will run some RT60 tests first to be sure it's needed, but my ears and experience (live sound and a bit of studio work) lead me to think that I do. Some of the Skylines would be mounted onto parts of my false wall, behind which is 2" Linacoustic, and soon some superchunks. As this will, for above-bass frequencies, be "replacing" absorption with diffusion, is it likely that this *will* increase my RT60?

Other spots I've eyed are directly fired at by my side dipoles and are now plaster. My thinking was that this would contribute to a greater sense of envelopment by the surround fields. Am I on the wrong track?

Thanks again.

Terry Montlick

08-09-06, 03:55 PM

You mean "diffusion" there, right?

I'm thinking of adding diffusors - Skyline LPs - to my theater to make it a bit livelier. I will run some RT60 tests first to be sure it's needed, but my ears and experience (live sound and a bit of studio work) lead me to think that I do. Some of the Skylines would be mounted onto parts of my false wall, behind which is 2" Linacoustic, and soon some superchunks. As this will, for above-bass frequencies, be "replacing" absorption with diffusion, is it likely that this *will* increase my RT60?

Other spots I've eyed are directly fired at by my side dipoles and are now plaster. My thinking was that this would contribute to a greater sense of envelopment by the surround fields. Am I on the wrong track?

Thanks again.
Yes, I meant "diffusion." :)

If you are mounting Skylines over what is now 2" thick Linacoustic, I wouldn't worry at all about driving down the reverberation time. You are effectively reducing the existing absorption by covering up some highly absorptive material. The studies I cited kept the absorption the same while changing the diffusion coefficients only. And a few small diffusers on the walls shouldn't measurably affect RT60, while they may signficantly enhance the sense of spaciousness.

- Terry

pepar

08-09-06, 04:15 PM

. . The studies I cited kept the absorption the same while changing the diffusion coefficients only. And a few small diffusers on the walls shouldn't measurably affect RT60, while they may signficantly enhance the sense of spaciousness.
That seems to be a THX-driven issue - envelopment. And personally, I like that feeling. But I rarely read anything on that. Home theater acoustics seem to be limited to RT60 and frequency response. CriticalListener mentioned his HAA Level 1 course touched on "sound waves become omnidirectional", but I'm not sure that could be contrued as envelopment. Your comment on spaciousness is one of the few on that topic that I've read from an acoustician. Am I just missing that discourse?

CriticalListener

08-09-06, 10:09 PM

That seems to be a THX-driven issue - envelopment. And personally, I like that feeling. But I rarely read anything on that. Home theater acoustics seem to be limited to RT60 and frequency response. CriticalListener mentioned his HAA Level 1 course touched on "sound waves become omnidirectional", but I'm not sure that could be contrued as envelopment. Your comment on spaciousness is one of the few on that topic that I've read from an acoustician. Am I just missing that discourse?
The point about omnidirectional was a topic at HAA training and is based on when listeners can no longer pinpoint where sound is coming from. For most people this occurs below 125 hz. Thus a sub placed in any part of a room, with the crossover set to 125 hz or lower, should be impossible for a blindfolded person to point to. This has nothing to do with envelopment.

However we all discussed in detail the important aspects of sound quality, which I remember by using the acronym FRED C. [Focus, Response, Envelopment, Dynamics, Clarity].

pepar

08-09-06, 11:42 PM

However we all discussed in detail the important aspects of sound quality, which I remember by using the acronym FRED C. [Focus, Response, Envelopment, Dynamics, Clarity].
Ahh yes, there it is; envelopment.

bpape

08-10-06, 07:03 AM

Having the ONLY sub in the room behind me is, to me, very distracting - even with an 80Hz xover. May just be me.

Also, especially with a 125Hz or 100Hz xover, it would have to be a very good sub with zero port noise, little to no distortion, etc - as those things are absolutely very localizable and can't be filtered with the xover.

Lastly, you have to have the flexibility to delay the sub enough to appropriately align with the mains - many receivers don't have enough play on the sub to do this. And, you can't do it with the phase control as some will try to do as that is frequency dependent.

Just a thought.

Bryan

Kal Rubinson

08-10-06, 11:36 AM

Having the ONLY sub in the room behind me is, to me, very distracting - even with an 80Hz xover. May just be me.As you indicate, it is implementation-dependant. However, for most applications, I use it for LFE and bass-manage only the rear channels. Thus, with a 70Hz crossover, sealed enclosure, servo-control and adequate delay (and phase and EQ) control, it works just fine for me. :D

Kal

bpape

08-10-06, 11:52 AM

Absolutely Kal. Every application is different.

Bryan

nowandthen

08-10-06, 02:24 PM

Whew! I just finshed reading through this entire thread.

One area that has not been discussed: Using a riser for a base trap. I have seen this mentioned but have not seen any discussion in this thread. Assuming I have a 12" riser that is roughly 12' x 9', can this be used for a base trap? If so how would that be done? Also, I do plan to add buttkickers to the risers if that matters.

Thanks,

Todd

Ethan Winer

08-10-06, 02:26 PM

pepar

08-10-06, 02:58 PM

Terry Montlick

08-10-06, 03:53 PM

Terry,

> I have observed, and the literature strongly suggests, that RT60 is lowered with added diffusion <

Also, many diffusors absorb as well as diffuse. RPG has absorption data for all of their diffusors, and the amount of absorption is not insignificant.

--Ethan
Yes, the added absorption for QRD-type diffusers which RPG publishes is over and above the diffusion-absorption effect I described.

- Terry

pepar

08-10-06, 03:57 PM

Yes, the added absorption for QRD-type diffusers which RPG publishes is over and above the diffusion-absorption effect I described.

- Terry
Are they absorbing frequencies that they are not diffusing? Are they absorbing any significant amount of the frequencies that they are diffusing?

Terry Montlick

08-10-06, 04:21 PM

Are they absorbing frequencies that they are not diffusing? Are they absorbing any significant amount of the frequencies that they are diffusing?
The QRD-specific absorption (which is measured in a diffuse sound field, via the standard reverberation room method) is significant. It was first noticed in concert halls in the early days of QRD installation. The RT60 became unusually low, and diffusers needed to be removed.

Since then, the theory for this extra absorption has been worked out by a researcher in Japan -- I forgot who. He also found that some kind of surface coating can reduce this absorption. My simplistic understanding of the theory is that the sharp changes in phase at adjacent QRD wells also causes pressure change, and this induces lateral air movement (much like adjacent high and low pressure weather systems) which removes energy via friction.

- Terry

BasementBob

08-10-06, 05:13 PM

Terry Montlick:

I believe QRD's are also quarter wavelength resonator absorbers [I probably phrased that a bit off].
And the absorption increases if you put a membrane (even acoustically transparent cloth) in front of a diffuser, according to RPG (recall that marketing page).

mschiff

08-11-06, 12:24 PM

Hi Ethan,

I downloaded your Real Traps Test Tone CD yesterday, and did a quick check of my home theater space. I set the level to 70db using the pink noise, and then just did a quick check at the beginning of each track. I had nothing below 60db, and nothing significantly above 80db. From 100 Hz up, I don't think it varied more then 5db either side of 70. Does this mean I'm in pretty good shape, or do I really need to check each tone?

-- Martin

pepar

08-11-06, 12:50 PM

ctviggen

08-11-06, 01:04 PM

The point about omnidirectional was a topic at HAA training and is based on when listeners can no longer pinpoint where sound is coming from. For most people this occurs below 125 hz. Thus a sub placed in any part of a room, with the crossover set to 125 hz or lower, should be impossible for a blindfolded person to point to. This has nothing to do with envelopment.

Based on my own tests, I simply do not believe this. I can EASILY point to a sub that's below 80 Hz (and even below 60 Hz). Get near 20Hz, then it becomes hard, but that's because I can no longer hear that frequency anyway.

Ethan Winer

08-11-06, 01:26 PM

Martin,

> just did a quick check at the beginning of each track. <

The whole point of that "CD" is to test every frequency. Otherwise you're missing the true extent of the peaks and nulls. I know it takes a while to run all the tones, but if you do that you'll be surprised (and likely disappointed) by how much more deviation you really have.

Look at the graph below, which was measured in a typical 16 by 10 foot room at 1 Hz intervals. As you can see, the true response varies enormously over very small spans.

--Ethan

http://www.realtraps.com/art_response.gif

CriticalListener

08-11-06, 01:29 PM

Based on my own tests, I simply do not believe this. I can EASILY point to a sub that's below 80 Hz (and even below 60 Hz). Get near 20Hz, then it becomes hard, but that's because I can no longer hear that frequency anyway.
That's quite impressive. While many studies have shown humans are incapable of localizing anything below 100hz, there are always people on the edge of the bell curves who are capable of amazing things.

Ethan Winer

08-11-06, 01:45 PM

Guys,

Often you can localize what seems like low frequencies by buzzes and rattles from nearby furnishings, and by distortion components that are well above the sub's crossover but still are emitted by the sub.

--Ethan

pepar

08-11-06, 02:00 PM

That's quite impressive. While many studies have shown humans are incapable of localizing anything below 100hz, there are always people on the edge of the bell curves who are capable of amazing things.
[small voice]Maybe his sub rattles or has port noise.[/small voice] :)

edit: Sheesh, I should hit F5 more often. Ethan already covered this.

Sirquack

08-11-06, 11:15 PM

nowandthen

08-13-06, 07:26 PM

If your riser is buttkicker driven, it may not be very effective as a bass trap.

Would you please explain the principles of using a riser as a bass trap? I'd like to understand how it is done. Is it more trouble than it's worth? Or is it just not a good place to make a bass trap.

Also, you said if I had buttkickers it probably couldn't be done. I'd like to understand why.

Sorry about the noob questions.

pepar

08-14-06, 10:49 AM

Would you please explain the principles of using a riser as a bass trap? I'd like to understand how it is done. Is it more trouble than it's worth? Or is it just not a good place to make a bass trap.

Also, you said if I had buttkickers it probably couldn't be done. I'd like to understand why.

Sorry about the noob questions.
Well, when it comes to this, I'm a noob as well. But here's my explanation. For bass traps, one can use gobs (a highly precise and technical term) of fiberglass or a resonance absorber, a bass trap designed so that its mass has a resonance at the frequency (or band) that needs to be "trapped" (absorbed). The trouble frequencies strike it and excite it, and the bass energy at those frequencies is removed from the room and converted into motion. If your riser is being driven by a buttlicker, it will have its own agenda and won't be free to absorb energy.

Theoretically, a riser could be used as a trap, but the resonance would change as different people sat on it. To me, that would seem to remove it as a viable trap.

Check my link and go to the riser design & construction. I built it with adding Buttkickers (or Clark Synthesis) in mind, but the darn thing has a fortuitous vibration that seems to be centered at 25Hz. So, when something happening in the soundtrack around that frequency - a quite common occurance in LFE - the riser vibrates. Is it trapping those frequencies? Of course. But that's not what it's for. When the monsters stomp, my audience feels it. With the first movie I played after completing it - Jurassic Park - I realized I needed no Buttkickers.

I'm sure someone (on this thread!) could design a riser to be a trap or just vibrate at a certain frequency (band) for a passive buttkicer-effect. Me? I got lucky.

BasementBob

08-14-06, 12:04 PM

Pepar:

Theoretically, a riser could be used as a trap, but the resonance would change as different people sat on it.Think helmholtz.

pepar

08-14-06, 12:28 PM

Pepar:

Think helmholtz.
Doh! Of course. It's called a "resonator" and not a "resonance absorber." :o

BasementBob

08-14-06, 12:54 PM

Two styles:
a) ported helmholtz -- with port in tri-corner (all modes active in tri-corners)
b) several 1/8" x ?foot long slots (cut with circular saw).

zductive

08-14-06, 11:47 PM

I have a 13' x 21' x8' dedcated theater. My acoustic treatment will be soffit absorbers plus 4" oc705 bass traps in the front corners. The rear wall opens at 50" high into a larger room.

I think that I want to coat the front wall with 1" oc703 spaced 2" off the wall. If I do this, should I frame each 2x4 piece and cover it with gom cloth? Should I wrap the poly bolster across the frame and into the space between boxes? OR, should I just mount the oc703 to the wall and tuft the gom at the corners of the insulation.

Can someone post a url to an example of a treated front wall.

Loking at this, I will have most of the oc703 behind the screen. I intend to mount the screen 6" off the wall with lightrope for illumination behind it.

I will also place one 2x4 panel at the sidewall reflection points.

Does this make sense? The room sounds reasonable now and has a large leather sofa 9' from the screen (92") I took car to space the speakers 3' from the side walls and the sub is 3' x 5' from the corner.

zductive

08-15-06, 12:25 AM

A little more info on the room.

Not to perfect scale.

The soffit would be 16" x 12 of oc703 along front and side walls.

dipole klipsch speakers are aligned with sides of sofa

92" screen
Any thoughts?

pepar

08-15-06, 07:42 AM

zductive

08-15-06, 02:45 PM

pepar

08-15-06, 03:20 PM

Thanks
I hadn't considered the false wall approach that you show. It looks like it may cut down on the construction time. However, it means that I will be doing more work inside the house.

Why did you select the 1" material over 2" oc703?

Did you find that the room was too dead when you finished?
The cavity behind the wall is lined with 2" Johns-Manville Linacoustic. The first reflection point absorbers are made from 2" Owens Corning SelectSound Black. I have 2" 703 from which I am going to make Studiotips SuperChunks. Info on them and a WHOLE lotta data can be found here (http://forum.studiotips.com/viewforum.php?f=8).

The room doesn't seem too dead, but I plan on taking some measurements when I start the trap project.

nowandthen

08-15-06, 08:26 PM

Thanks pepar and BasementBob. I think I'll forget trying to use the riser as a base trap. The two front corners are available as well as some soffit wall areas and floor wall areas.

KERMIE

08-17-06, 12:04 PM

pepar

08-17-06, 01:08 PM

I see that some people have their corner base traps starting on top of lets say a 7 inch high stage. When the base travels across the floor to into the corners does it hit the stage front which is usually wood/carpet and deflect? Newbie question...
That's not quite how bass frequencies "travel", but to keep it simple, they wash around something like a 7" stage like a huge wave would.

bpape

08-18-06, 06:47 AM

The size of the waves you're talking about are huge compared to a 7" stage. Also, you can't generally think of bass waves like rays. The higher you get, the more sound acts as you would think - hit something and bounce off. Bass radiates as a sphere and more of a wavefront.

BasementBob

08-18-06, 01:21 PM

Objects significantly smaller than the wavelength are ignored by the wave.
Objects significantly large than the wavelength cause the wave to bounce off.
http://www.bobgolds.com/Diffusion/DiffusionFrequency.GIF

pepar

08-18-06, 04:30 PM

BasementBob

08-18-06, 04:47 PM

pepar:
And in between?See the GIF link. Figure 4.2b.

Variations on this happen at the edges of free standing speakers (some diffusion in phase, some diffusion out of phase).

bpape

08-18-06, 10:29 PM

If the wave is even double the size of the object, it will pretty much ignore it. For a 7" height, that's up into the lower midrange.

Bryan

CriticalListener

08-20-06, 04:56 PM

Took the better part of two weekend, but I've finished two bass traps. After taking measurements (hopefully before summers out) I will decide if I need more bass traps. I did buy an extra box of insulation, so I'll just need the wood to build more.

I used my extra OC Acoustic Board {1" thick} on both sides to sandwich in the 4" of Knauff 6lb/ft insulation. Below is a picture of one, but the two are identical.

http://www.lookbig.com/dscf0302.jpg

pepar

08-21-06, 12:29 AM

zductive

08-21-06, 01:01 AM

I am getting ready to build two bass traps for the front corners of my theater.
The extremely unprofessional forum thread on bass traps installation (now closed) raised many questions that I hadn't considered.

Experts - please clear this up possibly a moderated thread is in order

I want to build corner traps that have two layers of unfaced oc705. The top bottom and sides will be made from 3/4" mdf. I am treating the trap as if it were a pressurized vessel. That is, the seams will all be caulked and care will be made to ensure that the foam is held tightly against the box. This is all because of the "information" in the referenced thread.

I can not run the corner trap from the floor to the ceiling. It sits on a carpeted riser and has to terminate below the crown moulding.

I don't want to have to build this piece again! It would be much easier to frame out the drywall (single 1/2" layer) so that the oc705 would be held against the frame. I would then forget about the top and bottom also.

Based on current knowledge (the referenced thread insists that the bass traps must be held in proximate contact with the walls and the top and bottom must be in place to maintain the spring constant (at maximum) How does this type of trap really need to be fabricated??? Please don't refer to existing threads. I would like to get some yes/no information from ethan/bpape etc. No catfighting guys.

I don't care about sabines etc., what is your opinion about how the corner bass trap (not superchunk) should be fabricated!

Why was the raytracing method shot down out of hand.

BasementBob

08-21-06, 02:09 AM

zductive:

You could click on any of the links from "ChristianG's Corner Traps" on down at:
http://www.bobgolds.com/

Similarly on this page
http://www.bobgolds.com/AbsorptionCoefficients.htm
any of the links between "Jon Risch's Absorbers" and "David French's absorption cloud design with aluminum guttering material"
should give you construction ideas.

And there's also ---k--- 's
http://racarris.com/HT/Corner%20Trap/
(with some text about it at
AVS Thread: Upgrades, Treatments & fun w/ ETF (http://archive2.avsforum.com/avs-vb/showthread.php?t=547122) )
I think he ended up making three short corner traps and was reasonably content that he had done so. The reason I reference this thread, even though you asked not to, is you wroteI can not run the corner trap from the floor to the ceiling. It sits on a carpeted riser and has to terminate below the crown moulding.and ---k--- both did that, and posted a bunch of good observations both human and ETF5 graphed.

I am getting ready to build two bass traps for the front corners of my theater.In an otherwise untreated room, I believe corner traps are an excellent LF bang for the buck/effort. All modes are active in tri-corners, so that's a good spot to put an absorber. (there are other alternatives to corner traps, but I'm unsure how to discuss them without using the temporarily evil 'Sabin' word.)

I want to build corner traps that have two layers of unfaced oc705. The top bottom and sides will be made from 3/4" mdf. I am treating the trap as if it were a pressurized vessel. That is, the seams will all be caulked and care will be made to ensure that the foam is held tightly against the box. Don't go gung ho on the sealing. If it has to be portable then simply glue and screw the wood (skip the acoustic caulk).

I don't want to have to build this piece again! It would be much easier to frame out the drywall (single 1/2" layer) so that the oc705 would be held against the frame. I would then forget about the top and bottom also. Sounds a bit like the Dave Portocarrero corner trap at http://www.bobgolds.com/TrapDave/home.htm (bottom two pictures).

Based on current knowledge (the referenced thread insists that the bass traps must be held in proximate contact with the walls and the top and bottom must be in place to maintain the spring constant (at maximum) How does this type of trap really need to be fabricated??? Don't bother going gung ho sealing the edges. Just keep the absorber touching the sides if you can. If there's a 1/4" gap some places, don't worry about it. (A 2" hole is just being lazy - fix it).

And of course, last but not least
Studiotips Corner Absorber (http://forum.studiotips.com/viewtopic.php?t=534)

Anyway, building a corner trap is not rocket science. The main points are:
a) put 4" of rigid absorption on 2' diagonal as tall as you can and in as many corners as you can and touching the drywall.
b) Cover it with something fire retardant that'll keep the fibers in place when the wind blows on them. If your room has lots of HF absorption already consider something HF reflective, otherwise something you can breath through.
c) any framing you might do is simply to hold (a) and (b) in place.

If you can make observations of what you hear that's different, that's great.
We want pictures!

zductive

08-21-06, 02:43 PM

Thank you Bob for a very reasoned response.

It appears that there is a controversy about the need for the corner panel to come in contact with the corner walls. The discussion is confusing but, the safe way seems to have the glass touching the walls.

I con't think that my original idea of 3/4" mdf on the sides is required even though, it would make the corner reflector stiffer and less transparent to lower frequencies.

The compilation of various traps is great.

I will proceed with caution. Hopefully, I can make a few measurements from my listening position before I continue.

Biggest problem is integrating the corner trap into the remainder of the wall structure. I intend to have 2" oc703 spaced 2" from the walls. Since the corner trap is laid back into the corner, I guess that the best approach would be to have the oc703 run up to the point where it intersects the corner trap.

The problem that I am trying to address is the mismatch between speaker sound when I go through the alignment process. Each speaker sounds different. I believe that it is the result of the differences in high frequency reflections in the room. Time for sidewall reflection baffles!

Thanks for comments!

BasementBob

08-21-06, 06:41 PM

zductive:

The problem that I am trying to address is the mismatch between speaker sound when I go through the alignment process. Each speaker sounds different.
(I'm not a fan of horizontal centers -- I don't care if the drivers are matched -- I prefer the fronts to be identical right down to the model number.)
In my basement I have three identical fronts that are good off axis, and four identical surrounds. There's a scene in Mission To Mars (http://www.amazon.com/gp/product/B00003CWU3) chapter 11, where the mission commander's voice goes through each of the 4 surround speakers one at a time in a seamless arc, as well as the three front speakers, demonstrating that all 7 speakers get individual signals with Pro Logic IIx -- and there's a big timbre mismatch between my fronts and my surrounds.
For my smaller HT I'm thinking of buying 5 identical speakers (two monopole surrounds).

Wall/floor/ceiling reflections (and SBIR) can make speakers sound different (because the reflections don't reflect all the frequencies evenly resulting in colouration) -- but I'm wondering if there's something different about your speakers themselves, or perhaps a blown driver.

Kal Rubinson

08-21-06, 08:05 PM

zductive:

(I'm not a fan of horizontal centers -- I don't care if the drivers are matched -- I prefer the fronts to be identical right down to the model number.)
In my basement I have three identical fronts that are good off axis, and four identical surrounds. There's a scene in Mission To Mars (http://www.amazon.com/gp/product/B00003CWU3) chapter 11, where the mission commander's voice goes through each of the 4 surround speakers one at a time in a seamless arc, as well as the three front speakers, demonstrating that all 7 speakers get individual signals with Pro Logic IIx -- and there's a big timbre mismatch between my fronts and my surrounds.
For my smaller HT I'm thinking of buying 5 identical speakers (two monopole surrounds).

Wall/floor/ceiling reflections (and SBIR) can make speakers sound different (because the reflections don't reflect all the frequencies evenly resulting in colouration) -- but I'm wondering if there's something different about your speakers themselves, or perhaps a blown driver.
I completely agree. Using pink noise, a timbre difference can be noted among my three identical front speakers but it is MUCH smaller than it was when I had the so-called matched and dedicated center speaker from the same company. Position in the room and relationship to other objects will affect any speakers but it always is best to start out with a match. BTW, I could further reduce the discrepancy with Meridian MRC but the change was small.

Kal

zductive

08-22-06, 11:26 AM

klipsch towers on left and right.
left goes shii
right goes shewww

High frequency reflection is not the same for both speakers. Could it be the large pain of glass - you bet!

pepar

08-22-06, 11:34 AM

klipsch towers on left and right.
left goes shii
right goes shewww

High frequency reflection is not the same for both speakers. Could it be the large pain of glass - you bet!
How does it sound with movies/music?

zductive

08-22-06, 12:13 PM

Sounds very good. No obvious distortion. Just annoying.

BTW - I did decide to go with the false wall approach that you show in your theater. Right now, I am trying to figure how I will bring the AC outlets to the front of the wall. Kind of tough if you bring the wall out 4" or more.

Monty Williams

08-28-06, 02:58 PM

I'm planning a remodel (mostly a change of furniture and surface treatments, i.e. change the color scheme of my GOM, carpet, and furniture) of my HT this fall/winter and wanted to get some feedback on if my acoustical treatments need to be readdressed. My room is used primarily for HD HT and HDTV, with minor usage for high resolution audio such as SACD/DVD-A.

I have attached a Visio of the current room which measures approximately 18' 5" x 24' 6" with 8', acoustical drop tile ceilings. Above the ceiling tiles, the ceiling joists are filled with 9" of rolled OC insulation.

I have a 110" Stewart GH RS on the front 18' 5" wall, and my primary seating position is about 11-12' away. The front wall is currently treated with 1" OC 703 from floor to ceiling. The side walls are treated similarly, except only the bottom 48" is treated, the top 48" or so is left untreated drywall. At the rear of the room a wet bar area is going to be built which is not shown in the Visio diagram, but there are no treatments currently on the rear wall.

The room is located in the basement, so behind all the walls is poured concrete. The external walls are standard 2x4 stud construction although they are staggered 1/2" away from the concrete. R13 insulation fills the void between the poured concrete and the inside of the drywall. The drywall is double layer/GG 5/8". The interior equipment closet at the rear left corner of the room is standard 2x4 with a single layer of 5/8" drywall with a Middle Atlantic Slim5 rack flush mounted with the wall as shown (a smoked plexiglass door covers the equipment). The floor is poured concrete with heavy padding and cut pile carpet.

L/C/R speakers are M&K S150 THX Ultra, SR/SL/SBR/SBL are M&K SS150 THX Ultra in tripole configuration. Subs are a pair of M&K MX350's controlled by a Velodyne SMS-1.

Any suggestions are appreciated.

pepar

08-28-06, 03:21 PM

I'm planning a remodel (mostly a change of furniture and surface treatments, i.e. change the color scheme of my GOM, carpet, and furniture) of my HT this fall/winter and wanted to get some feedback on if my acoustical treatments need to be readdressed.

I have attached a Visio of the current room which measures approximately 18' 5" x 24' 6" with 8', acoustical drop tile ceilings. Above the ceiling tiles, the ceiling joists are filled with 9" of rolled OC insulation.

I have a 110" Stewart GH RS on the front 18' 5" wall, and my primary seating position is about 11-12' away. The front wall is currently treated with 1" OC 703 from floor to ceiling. The side walls are treated similarly, except only the bottom 48" is treated, the top 48" or so is left untreated drywall. At the rear of the room a wet bar area is going to be built which is not shown in the Visio diagram, but there are no treatments currently on the rear wall.

The room is located in the basement, so behind all the walls is poured concrete. The external walls are standard 2x4 stud construction although they are staggered 1/2" away from the concrete. R13 insulation fills the void between the poured concrete and the inside of the drywall. The drywall is double layer/GG 5/8". The interior equipment closet at the rear left corner of the room is standard 2x4 with a single layer of 5/8" drywall with a Middle Atlantic Slim5 rack flush mounted with the wall as shown (a smoked plexiglass door covers the equipment). The floor is poured concrete with heavy padding and cut pile carpet.

L/C/R speakers are M&K S150 THX Ultra, SR/SL/SBR/SBL are M&K SS150 THX Ultra in tripole configuration. Subs are a pair of M&K MX350's controlled by a Velodyne SMS-1.

Any suggestions are appreciated.
Nice speakers; I have the same myself.

How does the system sound now? The best recommendation would be that you get some acoustical testing software and microphone and run some tests.

Monty Williams

08-28-06, 03:55 PM

Thanks. I really like M&K speakers and it continues to surprise me that they don't get talked about much here on AVS despite their use in movie/music studio monitoring and mastering.

I think my room sounds great now (better than it ever has), but the nature of this hobby is the endless pursuit of audio/video perfection. As much as we all like to think we've hit the nail on the head with our own HT, there's always room for improvement. Regardless of how many comparisons you do with other HT's/demo rooms/etc it's hard to say one is better than another unless there is an obvious problem due to our poor auditory memory. Plus you have all the other enthusiasts here commenting on their own rooms/HT's so it makes one wonder if there's more to be done.

While my room was built with HT in mind, there are some design/construction shortcomings and compromises. Your advice to have the room tested is a good one and I know that I should probably go ahead and do it, but I was just wondering if there were any glaring deficiencies that could be corrected prior to going that route in order to realize a more detailed assessment of my room's areas for improvement.

pepar

08-28-06, 04:23 PM

Thanks. I really like M&K speakers and it continues to surprise me that they don't get talked about much here on AVS despite their use in movie/music studio monitoring and mastering.
I know what you mean, but I posted a thread on upgrading them and drew out a slew of M&K owners advising against it. I'm guessing that we're a smug bunch not needing approval from anyone else to know what we've got. :D

I think my room sounds great now (better than it ever has), but the nature of this hobby is the endless pursuit of audio/video perfection. As much as we all like to think we've hit the nail on the head with our own HT, there's always room for improvement. Regardless of how many comparisons you do with other HT's/demo rooms/etc it's hard to say one is better than another unless there is an obvious problem due to our poor auditory memory. Plus you have all the other enthusiasts here commenting on their own rooms/HT's so it makes one wonder if there's more to be done.

While my room was built with HT in mind, there are some design/construction shortcomings and compromises. Your advice to have the room tested is a good one and I know that I should probably go ahead and do it, but I was just wondering if there were any glaring deficiencies that could be corrected prior to going that route in order to realize a more detailed assessment of my room's areas for improvement.
Making changes to a room that "sounds great now" without acoustical measurements would be like <enter smart-ass analogy here>. If it sounds that good already, there may be a tweak that would improve it, but you're more likely to go backwards.

Monty Williams

08-28-06, 05:53 PM

Do you know my wife or something? :D

Seriously, I guess I need to qualify where I'm at now before I decide to make any changes.

Dennis Erskine

08-28-06, 07:31 PM

BasementBob

08-28-06, 07:45 PM

Dennis Erskine:

The reason I say that is our hearing mechanisms are very good at adapting to "bad stuff" (the result is fatigue). I can't tell you the number of times we've been in "this room sounds great" My mother says in the same breath "I don't know why you spend so much time thinking about acoustics. My living room sounds great. BTW, thanks for the new DVD player. I really like the subtitles button. When I can't understand what they're saying I can just rewind and read it."

Monty Williams

08-28-06, 07:58 PM

How do you know it sounds great? :)
The reason I say that is our hearing mechanisms are very good at adapting to "bad stuff" (the result is fatigue). I can't tell you the number of times we've been in "this room sounds great" but after we calibrate the comment is "I had no idea it was so bad."

I would strongly advise having a pro do some extensive measurements to see where you are at. These initial plots can target areas for improvement (if any) and give you something to compare once changes are made.

You're right, as I mentioned my assessment of my HT is entirely based upon my limited experience with my previous environments and comparisons with other rooms (albiet admittedly via ear/auditory memory - also admittedly faulty at best ). I know my room is not perfect, possiblty not even ideal, hence my post here and interest in improving my situation. My area of expertise has nothing to do with this hobby or interest.

I'm all for having a "pro" come in and do measurements, I'm just wondering if there are any basics or otherwise glaring omissions I've missed prior to going through that exercise so that I can make it more meaningful be alleviating flagrent issues and focus more on "fine tuning".

If however, the proper starting point is simply starting with whatever you have whether it be a raw room or a room treated in any way, then that would be an appreciated suggestion as well.

Recommendations for the NW suberbs /North Shore of Chicago would be appreciated as well.

BasementBob

08-28-06, 08:30 PM

Monty Williams

You might enjoy having a look at this: Sencore 10 Steps to Optimized Sound (http://www.sencore.com/newsletter/Nov03/AudioCalpart2.htm)

Dennis Erskine

08-28-06, 08:54 PM

Monty Williams

08-28-06, 09:00 PM

Thanks Bob,

There's some good info there - some of which I've already considered and implemented, but some which I haven't. I think the responses to my initial and follow up posts confirm that if I want to quantify my efforts then I need to establish a baseline with what I have now.

However, I must point out that I can't recall a thread on this forum where someone had their room measured in raw form, incorporated the recommendations, and then remeasured after the the suggested corrections were made. I'm sure there have been some, but if anyone can point them out I'd be very appreciative.

I've been entertaining the idea of THX, Alpha, or the like, certification for about a year now, and I am most interested in pursuing it this fall/winter.

Monty Williams

08-28-06, 09:08 PM

Here's some starts:

LF/RF too far apart for imaging and sound stage
LR/RF too close to side and front walls (SBIR)
One of two subwoofers are mis-located
Rear surrounds have timbre mismatches
Where is the center channel with respect to the screen?
Center channel too close to front wall

Okay, what do I need to do to get more detailed information from you, i.e. let's talk about consultation. PM or email would probably most appropriate at this point I'm assuming.

However, I must quickly ask for clarification on one point though - Why would the rear surrounds have "timbre mismatches" when they are the exact same speaker as the side surrounds and all the tweeters are the same/timbre matched according to M&K?

Again, if it is appropriate to contact you via email/PM or via telephone please let me know. I'd like to get my remodel going this fall.

BasementBob

08-28-06, 10:00 PM

Monty Williams:

However, I must quickly ask for clarification on one point though - Why would the rear surrounds have "timbre mismatches" when they are the exact same speaker as the side surrounds and all the tweeters are the same/timbre matched according to M&K?

If the side surrounds are the same as the fronts, right down to the model number, then ignoring reflections and broken drivers/cones, they're as good a timbre match as you're going to get.

If the side surrounds have the same size drivers/cones as the fronts, but the speaker cabinets are different, or the configuration of the drivers (e.g. two midrange vs one midrange) is different, then there's a strong chance they are not timbre matched.

To try it yourself, throw in a copy of Mission To Mars (http://www.amazon.com/gp/product/B00003CWU3) and go to chapter 11. The sound of one man's voice is paned slowly through all speakers. With my setup it's easy to hear a difference between the fronts and the rears. I have three identical fronts, right down to the model number (no horizontal center).

BasementBob

08-28-06, 10:04 PM

Monty Williams:

However, I must point out that I can't recall a thread on this forum where someone had their room measured in raw form, incorporated the recommendations, and then remeasured after the the suggested corrections were made.

Alpha Certification example:
Building the Music Vault - part 1 (http://www.ultraaudio.com/twbas/twbas_20050915.htm), part 2 (http://www.ultraaudio.com/twbas/twbas_20051215.htm), and part 3 (http://www.ultraaudio.com/twbas/twbas_20060215.htm).

AVS thread: ---k---'s Upgrades, Treatments & fun w/ ETF (http://archive2.avsforum.com/avs-vb/showthread.php?t=547122) -- not the whole 9 yards, but it was the first one I thought of.

Monty Williams

08-28-06, 10:24 PM

Monty Williams:

If the side surrounds are the same as the fronts, right down to the model number, then ignoring reflections and broken drivers/cones, they're as good a timbre match as you're going to get.

If the side surrounds have the same size drivers/cones as the fronts, but the speaker cabinets are different, or the configuration of the drivers (e.g. two midrange vs one midrange) is different, then there's a strong chance they are not timbre matched.

All four surrounds are exactly the same, same model, same part number etc. The onle difference is the orientation each is facing so that the phase is correct. The surrounds are M&K's recommended match for the S150 L/C/R's (as well as the subs) I'm using. There is no mismatch, at least according to M&K, within my speaker system.

Obviously placement and room acoustics affect it afeter the fact, hence the purpose of my posts.

BasementBob

08-28-06, 10:32 PM

Monty Williams:

All four surrounds are exactly the same, same model, same part number etc.I meant are your four surrounds the same as your three fronts.

The surrounds are M&K's recommended match for the S150 L/C/R's (as well as the subs) I'm using. There is no mismatch, at least according to M&K, within my speaker systemI think this means the answer is no. The surrounds are different from the fronts.

To tell if they are timbre matched, try Mission To Mars.

Dennis Erskine

08-29-06, 07:43 AM

Timbre mismatch is due to the close proximity of the left rear surround to the side wall as contrasted to the distance of the right rear surround from any side boundry.

We can do a THX Certified Home Theater. Alpha Certification is Terry's domain.

Ethan Winer

08-29-06, 11:51 AM

Monty,

> I can't recall a thread on this forum where someone had their room measured in raw form, incorporated the recommendations, and then remeasured after the the suggested corrections were made. <

Here you go:

http://www.audioholics.com/productreviews/avhardware/realtrapsp1.php

It's written as a review, but it has exactly what you're asking for.

--Ethan

nowandthen

08-29-06, 08:34 PM

Monty Williams

You might enjoy having a look at this: Sencore 10 Steps to Optimized Sound (http://www.sencore.com/newsletter/Nov03/AudioCalpart2.htm)

From step 2 "Front L & R Main Speakers

Form an equilateral triangle with the center of the listening area

Locate at least 3 feet from walls

Position about 1/4 of room width from side walls & 1/4 of room length from front wall"

Realistically, how many of us have the room to do this, or perhaps should I say the desire to do this? In my 24' long room, according to this I need to place my fronts 6' out from the front wall. Therefore my AT screen needs to be 7' from the front wall. My 24' room is now effectively 19' long. Are there solutions to this ideal situation that won't eat up 1/4 of my room? e.g front wall treatments.

Thanks,

Todd

bpape

08-29-06, 10:04 PM

Remember the title "OPTIMIZED sound" (in their opinion). It says nothing about real world rooms or practical solutions. Unfortunately, there is no one perfect way to set up every speaker in every room.

Basic rules of thumb:

- Maintain symmetry left to right in front of you.
- Dont' put any speaker or any seat right up against a wall
- Place the seating first and let it guide the rest of the setup
- The equilateral triangle is a decent starting point but be willing to move from there.
- Be willing to treat the walls if the speakers (front) need to be placed close to the walls because you bought too big a screen or you have a very long narrow room.
- Set your speakers to small and let the sub handle the bottom. This lets you move the sub for best response without messing up imaging. The best place for your mains is almost never the best place for bass response.

Pretty much everything else is unique to a specific situation.

Bryan

pepar

08-29-06, 11:22 PM

From step 2 "Front L & R Main Speakers

Form an equilateral triangle with the center of the listening area

Locate at least 3 feet from walls

Position about 1/4 of room width from side walls & 1/4 of room length from front wall"

Realistically, how many of us have the room to do this, or perhaps should I say the desire to do this? In my 24' long room, according to this I need to place my fronts 6' out from the front wall. Therefore my AT screen needs to be 7' from the front wall. My 24' room is now effectively 19' long. Are there solutions to this ideal situation that won't eat up 1/4 of my room? e.g front wall treatments.

Thanks,

Todd
I've never seen a theater where LCR are that far from the front wall. Mostly, they are a few feet out or mounted ON the wall. Mine are like that, but I've treated the front wall with 2" J-M Linacoustic and am planning to add bass traps there as well.

Dennis Erskine

08-30-06, 07:15 AM

If your mains are crossed over with the sub(s) at 80Hz, the mains would be about 3.5' from the front wall. Since this isn't a practical solution in most cases, the front wall needs to be treated with a combination of absorption and diffusion to diminish boundary effects.

Andrew Hornfeck

08-30-06, 02:32 PM

WHAT would you suggest I use to attach 2' x 2' "accent" panels built of 1-1/2" Knauff board to my walls which are also made of GOM-covered Knauff panels. Does Velcro work? How about some kind of spike strips? Where can I buy them?

Kal Rubinson

08-30-06, 02:39 PM

You can buy spike strips cheaply at Home Depot. Also, take a look at the various models of RotoFast fasteners at http://www.rotofast.com A little pricey but elegant and effective.

Kal

Andrew Hornfeck

08-30-06, 03:46 PM

You can buy spike strips cheaply at Home Depot. Also, take a look at the various models of RotoFast fasteners at http://www.rotofast.com A little pricey but elegant and effective.

Kal
THANKS for the quick reply!

When you say spike strips, are you speaking of the mending plates they sell in the lumber/truss section or something else?

I'd never seen these Rotofast jobs -- I'm (essentially) attaching one panel TO another, so only the double one would work. That's why I was looking into the spikes or velcro.

Kal Rubinson

08-30-06, 04:11 PM

THANKS for the quick reply!

When you say spike strips, are you speaking of the mending plates they sell in the lumber/truss section or something else?Yup.

Kal

pepar

08-30-06, 04:15 PM

THANKS for the quick reply!

When you say spike strips, are you speaking of the mending plates they sell in the lumber/truss section or something else?

I'd never seen these Rotofast jobs -- I'm (essentially) attaching one panel TO another, so only the double one would work. That's why I was looking into the spikes or velcro.
Spike strips = I think are used to install carpet and are installed around the room's perimeter.

BasementBob

08-30-06, 05:37 PM

Kal Rubinson:

The rotofast looks cool -- I like that it can be used THROUGH fabric.

This is what I've done before: http://www.bobgolds.com/AbsorberMount/home.htm

Kal Rubinson

08-30-06, 09:17 PM

Kal Rubinson:
The rotofast looks cool -- I like that it can be used THROUGH fabric.
This is what I've done before: Nice. BTW, I used plastic stand-offs with the Rotofasts to space the panels off the wall.

Kal

CriticalListener

08-31-06, 09:07 AM

The rotofast looks cool -- I like that it can be used THROUGH fabric.
It looks so cool I emailed the company. Then I got back a Mail Delivery Error for info@rotofast.com, which cools my enthusiasm as I have to question their competence in either putting up the wrong email address or choosing a bad internet provider or, worst case scenario, failure to pay some bills.

Kal Rubinson

08-31-06, 11:39 AM

That address has worked for me. I understand your feeling but perhaps you might try again.

Kal

kiwishred

08-31-06, 04:18 PM

Based on what I have read in this thread I was contemplating making sound absorbers by placing a single 2'*4'*2" OC 703 panel in a 3" deep frame so it would be held out from the wall by 1". 3" total depth is as much as I want to go for aesthetics reasons.

However, the first source I have found for OC 703 in Seattle, R-Factor, only has 1" sheets. So, the questions I have are these:

1) If I stack two 1" sheets do I have the acoustic equivalent of a 2" sheet ? Is it necessary for them to be pressed tightly together to achieve this ? I am inclined to think so because, otherwise, some sound passing through the first sheet might reflect off the second sheet and therefore not get absorbed in the second sheet...

2) For a 3" total frame depth, rather than have 2" 703 + 1" back air gap, am I better off using 3" 703 and no air gap ? Use of 1" 703 allows this possibility whereas 2" panels do not.

BTW, here are some sources for unfaced, 2’*4’*1”, 3 pfc density, rigid fiberglass in the Seattle area (who will sell to the public):

R-Factor, 16750 Woodinville-Redmond Rd. Woodinville. 425-488-7600.
Owens Corning 703, $145 per pack of 24 sheets (192 sq feet). 75.5 c/sq foot

Bay Insulation, 7043 S 190th St, Kent. 425-251-6750.
Owens Corning 703, Sell by the sheet, 64 c/sq foot.

E J Bartells, 700 Powell Ave SW, Renton, 425-228-8807.
Johns Manville 814 "SpinGlas" (same acoustic specifications as Insul-SHIELD I/S 300 but targeted at duct insulation rather than general construction), $63.36 per pack of 18 sheets (144 sq feet). 44 c/sq foot

Note: "SpinGlas/Insul-SHIELD has nominally better absorption ratings than OC 703, eg:

http://mysite.verizon.net/kiwishred/HTS/absorber-compare.gif

However, I suspect this might just be measurement variability.

Brent

BasementBob

08-31-06, 04:31 PM

kiwishread

1) If I stack two 1" sheets do I have the acoustic equivalent of a 2" sheet ? Yes.

Is it necessary for them to be pressed tightly together to achieve this ?No.
However, it's better to have them pressed together so that they are both out from the wall as far as possible within that 3".

I am inclined to think so because, otherwise, some sound passing through the first sheet might reflect off the second sheet and therefore not get absorbed in the second sheet...Don't worry about it.

For a 3" total frame depth, rather than have 2" 703 + 1" back air gap, am I better off using 3" 703 and no air gap ? Yes, but not much.

RyanJNielson

08-31-06, 05:39 PM

jandawil

08-31-06, 05:48 PM

Hey, guys-

I'm building my dedicated HT room and have a question:

The room is 8 x 12.5 x 17.5 and I am planning to line my side walls with 1" Linacoustic RC (up to ear level). I am also planning to cover the front wall (floor to ceiling) with 1" of the Linacoustic. With a 100' roll, I'll still have about 40' of Linacoustic left over.

My question is this:

Would it be feasable to cut the Linacoustic into triangles and stack them floor to ceiling to provide some rear-room bass absorption?

I am planning some good sized superchunk style front-room bass absorption using 5.5" acoustical cotton.

What do you think...?

That would be a lot of cutting if you used 1" material as opposed to 4", plus to my knowledge linacoustic is not very dense. You want something more dense that will give you better absorbtion at the lower frequencies such as OC703 or in my case I used Roxul mineral wool. It was only $78 for enough to do 8' high corner traps 24" across. I'm sure others more knowing than I will also pipe in

RyanJNielson

08-31-06, 06:01 PM

Thanks for the tip, Jon-

Rockwool seems to be a great solution for my corners. VERY economical!

Great job on your theater, btw!

jandawil

08-31-06, 06:05 PM

Thanks for the tip, Jon-

Rockwool seems to be a great solution for my corners. VERY economical!

Great job on your theater, btw!

Thanks man!!! It's always a work in progress but I'm really enjoying it. Good luck with your project.

nowandthen

08-31-06, 08:35 PM

Remember the title "OPTIMIZED sound" (in their opinion). It says nothing about real world rooms or practical solutions. Unfortunately, there is no one perfect way to set up every speaker in every room.

....

I've never seen a theater where LCR are that far from the front wall. Mostly, they are a few feet out or mounted ON the wall. Mine are like that, but I've treated the front wall with 2" J-M Linacoustic and am planning to add bass traps there as well.

If your mains are crossed over with the sub(s) at 80Hz, the mains would be about 3.5' from the front wall. Since this isn't a practical solution in most cases, the front wall needs to be treated with a combination of absorption and diffusion to diminish boundary effects.

Thanks Bryan, pepar and Dennis. I knew the 6' from front wall was not realistic for most people. I'm glad to heat the experts have "ways" to compensate.

Todd

pepar

08-31-06, 10:33 PM

Thanks Bryan, pepar and Dennis. I knew the 6' from front wall was not realistic for most people. I'm glad to heat the experts have "ways" to compensate.

Todd
FYI, the other two are experts. :)

zductive

09-04-06, 12:27 AM

Can anyone direct me to a diy for an acoustic soffitt??

I am planning to install a 16w x 10 h " soffit made from oc703 material and wrapped in gom. The soffit will wrap across the front stage and then down the two sidewalls.

If I am lucky, I can incorporate a hushbox into an extension of the soffitt across the room at the projector location.

I am having a little trouble determining what the internal structure of the soffit should be. Also having a little trouble with how the edge away from the wall should be supported.

The soffitt will be a little heavier because I am going to install miniature downlights from HD (low voltage).

BasementBob

09-04-06, 12:31 AM

zductive:

There's a bunch of ways.

Here's one:
- Build a bunch of downward struts on 2' centers.
- Then build a ladder (two 12' 2x2's with 13" 2x2's across on 2' centers)
- add extra cross pieces (ladder steps) where the lights will go.
- Then screw the ladder to the downward struts.
- build wood boxes lined with drywall for the lights, and put them in place
- wire the lights, and run any speaker wire or other wires you intend to use
- run any HVAC ducts you want to run.
- Fill it with 703 (notches optional, duct stocks cuts optional, put them in diagonally, turn them upright).
- Cover it with GoM
- Add trim over the staples.

Another variation:
- build two ladders (two 12' 2x2's with 7" 2x2's across on 2' centers)
- turn it into a box frame by adding more 7" 2x2's to join the ladders
- fasten it to the walls and ceiling.
-

zductive

09-04-06, 09:53 PM

Bob - your on the right track but, I was thinking more about the soffit bass traps that ASC sells http://www.asc-home-theater.com/products-soffit2.htm.

What does the internal structure of that trap look like?

It looks like it is two pieces of oc703 wrapped in cloth. What I can't see is how the two pieces are held together structurually and what the track looks like.

Any ideas?

T

Scott Mat

09-05-06, 02:48 PM

I have a small room in my basement that I am considering adapting to use as a HT. It has sheetrock walls and a drop ceiling. Should I re-sheetrock with green glue? What can be done about the ceiling and floor (carpet over concrete)?

Thanks,

Scott

BasementBob

09-05-06, 02:57 PM

zductive:

I don't know. You could buy 2' of them and find out.
I'm guessing it's foam; eor two pieces of 703, each fully wrapped in GoM, with 90 degree bent clothes hangers, and glue on the join.

However, if you want to build it that way (hollow inside), you could try a variation on this with sheet metal or aluminum guttering as framing: http://www.recording.org/ftopict-26889.html

BasementBob

09-05-06, 02:58 PM

Scott Mat:
That sounds to me like a question for your own separate thread.

kiwishred

09-06-06, 03:33 AM

myfipie

09-07-06, 06:56 AM

IMO it is just a extra precaution. I have never heard of fiberglass even leaking out of burlap. Now if you HIT the panel with a bat I am sure something would come out.

Glenn

nirvana_av

09-07-06, 09:30 AM

Is speaker cloth (specifically the black polyester variety that can be had from Joann fabrics for about $7 per 60" wide yard) sufficient to contain all the nasties that might potentially flake off rigid fiberglass ?

I have seen some people add a layer of batting but then others just wrap their naked OC 703 in nothing but burlap. So I am wondering if the batting is really necessary or just an extra precaution for the sake of peace of mind ...

TIA,
Brent

I have had success using the very thin, dark gray fabric similar to what you will find covering the bottom of upholstered chairs and sofas. I attach it to the fiberglass using 3M Super 77 spray adhesive. The fiberglass panel is then inserted into a GOM wrapped wood frame. This provides one more containment for the fibers if you are concerned. On the other hand, I've also applied GOM directly to OC705 and I haven't seen any evidence of fibers coming through.

chillinintheoc

09-07-06, 07:54 PM

I need to buy some 1" Linacoutsic...how much is that stuff for a roll?

chillinintheoc

KERMIE

09-08-06, 03:37 PM

Was it ever really decided if a corner bass trap Floor to ceiling is better as a:

1. 24 inch triangle filled with wedges of acoustical cotton from top to bottom

or

2. Roughly 3-4 " thick just across the face and a 45 degree angle, a space from there to the wall corner.

In my room I wanted to do 4 corner base traps floor to ceiling but I can only do the back two walls. The front corners have a corner trap, floor up to 52" then a tri corner by the ceiling.

I still have to do the back corners and wanted to know the best solution.

Room is 13 x 17

thanks

Stima

09-08-06, 07:10 PM

Good question...I don't recall any definitive comparisons. I am eager for a reply as well.

bpape

09-09-06, 08:38 AM

If all else is equal, the solid ones will reach a bit deeper into the bottom end more effectively. In effect, you'll use the same amount of material to do a solid one as you would to do a 6" thick straddling panel.

Bryan

myfipie

09-10-06, 08:38 AM

GetGray

09-10-06, 01:48 PM

pepar

09-10-06, 02:10 PM

Can you elaborate, I'm not following. Do you mean the solid triangle literally in the corner is more effective than the panel straddling the corner? If it's less material and more effective, why wouldn't everyone do it that way?
I think I picked up that the same amount of material is used as in a 6" "straddling" type. Previously, the cross-corner style with a 3"-4" thick panel had been discussed.

bpape

09-11-06, 07:32 AM

Yes. If you do the solid chunk, you're going to have a 17x27x24" corner with the farthest part being out 12" from the corner at 45 degrees.

If you have a 6" thick panel (2' wide and framed so about 25.5") straddling the corner, the BACK of that panel will be at 17" (along the wall) from the corner - 12" out at 45 degrees. From there, it will stick out another 6".

In addition, for the same amount of upper bass, mid and HF absorbtion, you'll get slightly better really deep bass control.

Bryan

GetGray

09-11-06, 08:22 AM

... 17x27x24" corner with the farthest part being out 12" from the corner at 45 degrees.You meant 17x17x24 I presume. In addition, for the same amount of upper bass, mid and HF absorbtion, you'll get slightly better really deep bass control. to be sure I am clear, you meant slightly better when using the solid design.[/QUOTE]Let me know if I have that incorrect. Thanks for the clarification.

pepar

09-11-06, 08:46 AM

You meant 17x17x24 I presume. to be sure I am clear, you meant slightly better when using the solid design. Let me know if I have that incorrect. Thanks for the clarification.
Corner Absorption Comparision test (http://forum.studiotips.com/viewtopic.php?t=536&start=0&postdays=0&postorder=asc&highlight=)

GetGray

09-11-06, 09:21 AM

That appears to show foam outperforming the fiberglass. Thought the foam wasn't so good realtive to the FG?

pepar

09-11-06, 09:28 AM

That appears to show foam outperforming the fiberglass. Thought the foam wasn't so good realtive to the FG?
I think the point of the test was to show that the DIY SSC (Studiotips Super Chunk) performed nearly identical to a commercial bass trap.

Meddy

09-11-06, 10:59 AM

A quick question for the experts. I have just completed framing out my basement and had to box-in two I-beams with the heating ducts in between (8' span). This "box " hangs approx 1' down from the ceiling,and is 14' wide (width of room) The two faces of the box are approx 12" high, 6" deep from face of 2x4's to the I-beam. Is it of any benefit to stuff this opening with Safe and Sound and cover with GOM and use as two bass traps, even though the trap wouldn't straddle the ceiling/box intersection? I plan on two super chunk style bass traps from floor to ceiling at the back of room (room is 29' long) and wondered if the 2 faces of the box would add anything or should I just drywall over them. Thanks

KERMIE

09-14-06, 06:28 PM

I have a question on my wall treatment bottom half.

I am using a 1" acoustical cotton behind GOM with 1 1/4" frames to keep it a little off the wall.

After I put the frames up it seems like the padding is not touching the GOM and I am afraid that it is laying up against the wall.

My concern is that when you push on the GOM it is just tight fabric and you have to push down hard to feel the padding.

I know most of the HT's that I have been in when you push on the walls it is like a firm mattress like feel. What am I going to experience in the future with sound and GOM issues..?

thank you

bpape

09-14-06, 10:49 PM

If you're using 1" cotton with only 1/4" behind it, it really doesn't matter. That 1/4" won't make diddly difference. If you want a nice padded feel (for those that must poke walls...), put a 1/4" slat across the back at 1/4, 1/2, and 3/4 of the height of the panel.

Bryan

Stima

09-15-06, 01:14 AM

I went the other route. Since fiberglass panels measure nearly exactly 1" thick...I made "picture frames"on my walls using long pieces of 1.5" x 8' x .75" boards with 1.5"x 1.5" x 1/4" cut spacers\shims. Instead of running the 1/4" material the full length behind the .75" material, I only placed the spacers\shims where I nailed gunned through the into a stud. On pieces that didn't have a stud to nail, I put in drywall anchors and used screws. This required drilling through holes in the wood, but it worked almost as well as the nail gun nails into studs.

After the frame was up and the fiberglass installed, I then stretched GOM from frame piece to frame piece over the fiberglass. For each wall, I ran two pieces of GOM the of the length of the wall room. (Two pieces since GOM is 64" wide and my room was 96" high.) This left GOM "seams" at each frame piece which I covered with stained wood "chair rail" pieces, floor board, and crown molding.

Whatever you do...do NOT try and use cotton batting in places you don't have acoustical cotton. The batting will NEVER maintain the same "thickness" and your eye will ALWAYS know where the two materials are different. If I had to do it over, I would simply put drywall or particle board in the places I didn't use fiberglass to maintain the proper depth.

tek-noid

09-18-06, 10:50 PM

After calling a dozen+ "local" (within 100 miles) HVAC distributors, I've had no luck finding Linacoustic, Insulshield, etc. I do have a line on "Knauf Wall & Ceiling Liner M", but all I know of its properties are a 1.5 PCF and a NRC of 0.70.

Q1. Does anybody know if this is a suitable replacement for Linacoustic, 703, etc?

Q2. I've asked this dealer (as well as an e-mail to Knauf) what the Absorption Coefficients are for this material, as they aren't posted on the website. Of course, I don't know what do with this info when/if I get it. If I compare this data with comparable product data from http://www.bobgolds.com/AbsorptionCoefficients.htm, what tolerances are acceptable?

Thanks,
James

Terry Montlick

09-19-06, 09:47 AM

Hi James,

This is a tough call, because "suitable replacement" is hard to define. Most home theaters are (unfortunately) not designed to particular acoustical specifications. If I had designed and modeled a theater which required 2.25-3 pcf fiberglass, then 1.5 pcf would not be a suitable replacement.

Knauf's published absorption coefficients for this product are:

1.5 PCF 1" .18 .36 .59 .86 .95 .90

However, there is also a 2 pcf version with the following published absorption coeffficients:

2.0 PCF 1" .25 .35 .69 .89 .96 1.01

If your supplier can get the 2 pcf Knauf, I would use that instead. BTW, I don't rely on any single set of reported absorption coefficient measurements, since the reverberation room method has a pretty high margin of error. We have our own proprietary absorption coefficent database.

Regards,
Terry

Felgar

09-22-06, 01:19 PM

This is a question on the general principles of sound absorbtion, as I find I'm usually better able to understand real-world situations by first understanding the underlying scientific/physical mechanisms in play.

I'm wondering what is it about a material that makes it able to absorb a sound wave. It is known that 3" of pink fiberglass will pretty much absorb all of the sound at 10,000 Hz, but very little at 40 Hz. Why is this? What is it about the higher frequencies that make them able to be absorbed by insulation (or ANY material for that matter), and what is it about lower frequency sound that enables it to pass right through insulation without being touched?

These questions drive a desire for me to understand how to effectively treat a room for appropriate bass atenuation, and it comes as a result of a conversation I has with a dealer about room accoustics. Intuitively it made sense to me that a thicker material might be needed in order to absorb a longer wavelength (lower frequency) sound wave. So I was asking the dealer how much of a corner will a bass trap that's effective down to 50Hz take up? Like, will a triangle of pink insulation in the corner that spans a distance 18" out from the corner on each wall work?

The response I got is that sound absorbtion is much more dependent on mass than shape. So I got to wondering, could a 1 or 2" thick panel in the corner work as a bass trap if it was heavy enough? Can a 1" thick layer of sand (being very heavy) over a wall effectively absorb the low frequency sound hitting the wall? One of the heaviest foams I know of comes in the form of those blue foldout gymnastic mats... Maybe that material could make an effective low frequency absorbtion material...

Terry Montlick

09-22-06, 02:01 PM

I'm wondering what is it about a material that makes it able to absorb a sound wave. It is known that 3" of pink fiberglass will pretty much absorb all of the sound at 10,000 Hz, but very little at 40 Hz. Why is this?
There's more going on than the following description, but a simple explanation of absorption in porous material like fiberglass involves material thickness vs. wavelength. A material can only absorb sound if its depth is at least some reasonable fraction of a wavelength (like 1/8).

To get the wavelength in feet of any frequency, divide 1000 (speed of sound) by that frequency. So a 10,000 Hz wave has a wavelength of 1/10 ft ~= 1". 3" fiberglass is 3 wavelengths thick, and has no trouble absorbing this sound.

A 40 Hz wave has a wavelength of around 1000/40 = 25 feet = 300". The 3" fiberglass is only 1/100 of this wavelength, so it can do very little to absorb it.

Regards,
Terry

Felgar

09-22-06, 02:28 PM

Ok, that's exactly what I was wondering, and is also more in line with what my intuition was telling me originally... So lets say pink fiberglass can absorb frequencies of wavelengths up to about 8 times its thickness. So 3" might absorb well until about a 24" wavelength, or a frequency of 500 Hz. Would putting it on a wall work to double the effectiveness because the wave has to travel in and then back out after reflecting off the wall?

And can I assume that different materials will have different properties for effectiveness? Like, maybe the special insulation that's supposed to improve sound isolation may be able to absorb 10 or 12 times it's thickness instead of just 8?

And of course, is there any documentation that can be found on what materials work in what way?

Ethan Winer

09-22-06, 04:44 PM

Felgar,

To expand on Terry's explanation a bit:

The reason fiberglass absorbs best when a substantial portion of the wave fits within its thickness is because "porous" absorbers like fiberglass act on wave velocity. If you picture a sine wave in your mind, the portion where the wave is all the way at the top or bottom has more velocity (greater absolute level) than the portions near the center.

When a sound wave hits a room boundary the velocity is zero at that point, and rises as you get farther from the wall. At 100 Hz the wave achieves maximum velocity 34 inches away from the wall. At 1000 Hz the maximum is only 3.4 inches away. So fiberglass four inches thick appied to the wall will absorb 1000 Hz completely, but at 100 Hz the wave has barely gotten started, so to speak, so there's not much to absorb.

I think of porous absorbers as working sort of like a person trying to run through chest-high quicksand. If you don't try to walk too fast you can slog your way through it. But the faster you try to go, the more friction is created and the harder it is to proceed. Fiberglass (and acoustic foam and rock wool etc) all work by creating the same sort of friction, but in this case for sound waves.

> Would putting it on a wall work to double the effectiveness because the wave has to travel in and then back out after reflecting off the wall? <

No. If you think about it, travelling through the material twice happens no matter how thick the material is or how far it's spaced away from the wall.

--Ethan

kiwishred

09-22-06, 09:43 PM

Ethan -

You could have saved some typing by quoting your own excellent article (http://www.ethanwiner.com/acoustics.html#air%20gap) on the subject :). Also, I found this article (http://www.kemt.fei.tuke.sk/Predmety/KEMT320_EA/_web/Online_Course_on_Acoustics/absoprtion.html) describing different types of absorbers, including porous.

Let me add a couple of speculations:

- I think you actually mean the particle velocity not the wave velocity, no ? The distinction being that the wave velocity is an intrinsic property of the propagation medium (it is a constant for a given material, temperature, etc) whereas the particle velocity is extrinsic (it varies in space and time) and describes how fast the air molecules themselves are moving.

- The problem with using a high density material is getting the sound to get into it in the first place. If it is too dense then too much of the sound will be reflected from the front surface and it won't matter how good an absorber it is.

I say speculation above because I am still in the process of digesting all the information in this thread myself.

Brent

Terry Montlick

09-23-06, 09:09 AM

Let me add a couple of speculations:

- I think you actually mean the particle velocity not the wave velocity, no ? The distinction being that the wave velocity is an intrinsic property of the propagation medium (it is a constant for a given material, temperature, etc) whereas the particle velocity is extrinsic (it varies in space and time) and describes how fast the air molecules themselves are moving.

- The problem with using a high density material is getting the sound to get into it in the first place. If it is too dense then too much of the sound will be reflected from the front surface and it won't matter how good an absorber it is.

I say speculation above because I am still in the process of digesting all the information in this thread myself.

Brent
Correct, Brent! Higher density means higher flow resistance. The exact relationship depends on the material, in ways that we don't fully understand but can at least measure. For a material of a certain flow resistance, there is an optimum absorption thickness for a given frequency. Much thinner, and the porous absorber is not very effective due to wavelength size, as you already know. Much thicker, and the higher flow resistance (higher acoustical impedance) kicks in and prevents some of the wave from getting into the material to be absorbed.

Regards,
Terry

pepar

09-23-06, 09:46 AM

Correct, Brent! Higher density means higher flow resistance.
Eureka! That's right, we are talking about moving air molecules! Slow the air molecules, attenuate the frequency.

Caspyr

09-24-06, 06:56 PM

Stima

09-25-06, 01:31 AM

My room is identically shaped but slightly smaller.

For my room, I built a 10" riser in the "back\square" portion of the room and built my screen (with curtians) in front of the half hexagon making the room appear square. This allowed me to put all my front speakers behind the screen. My sound stage is nearly perfect as I have all speakers at the exact same height at midpoint of the screen.

Acoustically I treated the room as follows:

Entire hexagon area and side walls up to the first row of seats: fully lined with 1" OC703. I lined the ceiling behind the screen as well.

Side walls after first row of seats and rear wall: 50% coverage with 1" OC703. The other 50% areas I used cotton batting to fill in the 1" space. I SERIOUSLY regret this however as the batting pushes against the GOM covering it producing a "bubble" effect. Even stretching the material as best I could did not remove this bubble and some minors puckers.

Bass traps: I put "super chunk" style traps (made of OC703) in the ceiling to wall corners behind the screen. I also built a very large, free standing frame to hold 12, OC705 sheets. (2 sections at 6" thick each...held 4" off the wall). The back piece of 705 has FSK facing the front wall.

I also put a 8' long "super chuck" style trap behind the rear row along the back wall\ riser floor corner.

All in all, I would have liked to have a little more bass trapping in the back corners (especially the tri-corners), but I just didn't like how they looked. The bass response is actually nearly perfect in the back row. There is a slight room mode in the front row giving a hump around 100hz. Its not horrible, and I may look into controlling it with a BFD.

I can share picks of how I did all the acoustic stuff if you wish...just let me know.

Hope this helps.

pepar

09-25-06, 09:23 AM

Wow, really long thread, and I am trying to get through it all.

My room is 22' long and 18.5 wide, but it isn't square. At the 16' mark the rest of the rear is "half a hexagon", like the top half of a stop sign.

What do you do for a room like that. I have 1" channels built in to all the moulding and around the windows to put in panels or whatever, just have no clue how/what I need.

I think it sounds way good now, what will putting the extra money in do for me.

If it matters, I have Martin Logan SL3's up front and Aerius in the rear.
Hopefully, you'll get the brians, the terrys and the ethans to comment, but from my limited knowledge I'd say that there's no way to "predict" how it will sound, and therefore know what treatments to install. All of the spreadsheets and calcs I've seen are for rectangles and - horrors! - squares. More sophisticated acoustical modeling is no doubt available, but not as a free or relatively free download. The best recommendation may be for you to consult/hire a professional to analyze the room. (This advice is from someone who's a devout DIY'er.)

As for the windows, I will go out on a limb and say that the more complete your light control is, the better it will be for the video part of the theater.

Caspyr

09-25-06, 11:49 AM

I can share picks of how I did all the acoustic stuff if you wish...just let me know.
I would love to see any pics. The hex part of my room is the back, two Berk's on a platform in the center of it. I would have to totally rebuild to put the screen back there, and I think losing that extra 5 feet would make th room to small for my 123" screen.

As for the windows, I will go out on a limb and say that the more complete your light control is, the better it will be for the video part of the theater.
There are five total windows, double wide on the side walls, and singles on each of the "hex" walls, all completley light controlled. Black fabric covered panels that fit fit snugly into the window frames. It's wired for curtains, but I like the look of the panels and they work great.

Light control is "perfect" right now, as a flat black room, you are blind in the room if the lights are out and the projector isn't on.

Ethan Winer

09-25-06, 12:46 PM

Caspyr,

> What do you do for a room like that. <

You'd place bass traps in the corner sections as usual. Even if the angles aren't 90 degrees, bass waves still collect there. In fact, a concave shape is bad generally (focuses sound back at you), so you'll need broadband absorption there, not just bass trapping.

> I think it sounds way good now, what will putting the extra money in do for me. <

Make it sound way better. :D

Seriously, most people who have never experienced the improvement acoustic treatment makes are blown away when they hear if for the first time. Now all of a sudden you can actually hear the pitch and articulation of every bass note. And when the first reflection points are treated the sound opens up to be much wider and, even more important, much clearer.

--Ethan

Caspyr

09-25-06, 01:40 PM

You'd place bass traps in the corner sections as usual.

Either corner in front would be tough to do anything. Looking at the screen the left side is the entry. The door is about 2 ft back from the screen edge. The other side is the audio cabinet doors.

pepar

09-25-06, 03:41 PM

Light control is "perfect" right now, as a flat black room, you are blind in the room if the lights are out and the projector isn't on.
I'd say you've got that taken care of. :)

Ethan Winer

09-26-06, 04:18 PM

pepar

09-26-06, 04:55 PM

Caspyr,

> Either corner in front would be tough to do anything. <

Every (rectangular) room has 12 corners, including where walls meet other walls, plus where they meet the ceiling and floor.

--Ethan
I *think* he was referring to "corner" as in "Go sit in the corner." Gravity being what it it, it tends to limit the number of corners one can actually sit in. :)

Ethan Winer

09-27-06, 03:31 PM

I *think* he was referring to "corner" as in "Go sit in the corner." Gravity being what it it, it tends to limit the number of corners one can actually sit in. :)

Huh? Here's what I read:

"You'd place bass traps in the corner sections as usual."

"Either corner in front would be tough to do anything."

What did you read?

pepar

09-27-06, 03:35 PM

Huh? Here's what I read:

"You'd place bass traps in the corner sections as usual."

"Either corner in front would be tough to do anything."

What did you read?
HEY, look over there! :)

Caspyr

09-27-06, 04:30 PM

What I am trying to say is that at the left of the screen, there is no corner. Currently about 2' behind the sceen on the left side is a curtain that is the entrance. The left side wall heads straight down past the screen, then a curtain, then the hallway to the rec room/bar area.

Plus, I was thinking of "corners" being where walls meet. I was not thinking top corner/bottom corner where the walls meet ceiling/floor. I am a 1k brain, to me a room has 4 corners not 8 :)

That's why I need places like this, gotta love the amount of information you can get from all you guys. Thanks !!

kiwishred

09-28-06, 03:05 AM

In the spirit of giving back something to this great thread, here are construction details for my absorbers (ideas borrowed from here and Bob Golds (http://www.bobgolds.com)).

I chose to go with an open frame construction for reasons of (a) light weight, (b) open sides for greater total area of fiberglass exposed, & (c) ease of custom-tailoring thickness. For room aesthetics reasons, total thickness was limited to 3”. I used a stack of three 1” sheets of 3 pfc rigid fiberglass in each frame. However, the construction method would also easily allow 2” of fiberglass with a 1” gap to wall (or any other desired combination). While the third sheet might not increase acoustic absorption much, it apparently does no harm and only adds a relatively small incremental cost ($3.52).

http://mysite.verizon.net/kiwishred/HTS/AcousticAbsorber/Clamps_DSC02169.JPG
Top and bottom frames constructed from 3/4”*1/2” hemlock and clamped square. Top frame used “shoe” moulding and mitred corners to provide a rounded front edge. Bottom frame used rectangular molding and butted corner joints.

http://mysite.verizon.net/kiwishred/HTS/AcousticAbsorber/Nailing_DSC02170.JPG
Nailing and gluing the top and bottom frames together. Pillars are 2 1/8” for 3 1/8” total thickness.

http://mysite.verizon.net/kiwishred/HTS/AcousticAbsorber/Mitre_DSC02185.JPG
Drilled guide holes for the #17 * 1” wire nails used to tack the mitred top frame pieces onto 3/4" square pillars using a cut-off #18 * 1” nail (an old trick my dad taught me :) ).

http://mysite.verizon.net/kiwishred/HTS/AcousticAbsorber/Finished_DSC02173.JPG
Front views of finished raw frame (left) and completed, covered, frame (right).

http://mysite.verizon.net/kiwishred/HTS/AcousticAbsorber/FabricCorner_DSC02181.JPG
Speaker cloth stretched and stapled onto frame following instructions here (http://www.rexart.com/stretching.html). Cloth is actually a lot darker than it appears in this photograph. Yellow stuff is the "rigid fiberglass" acoustic absorber.

BOM (per absorber):
- 4’ * 2’ * 1” Johns Manville 3 pfc rigid fiberglass sheets. Source: E J Bartells, 700 Powell Ave SW, Renton, WA. 425-228-8807. Cost: 3 sheets @ $3.52 = $10.56.
- 3/4” * 1/2” hemlock 1/4 rounded shoe for front frame. Source: Lowes. Cost: 2 8’ lengths at $3.36 each = $6.72.
- 3/4” * 1/2” hemlock “rectangle” (for back frame and 6 mid posts). Source: Lowes. Cost: 2 8’ lengths at $3.36 each = $6.72.
- 3/4” * 3/4” hemlock square (for pillars). Source Dunlumber. Cost 2’ @ 85 c/foot = $1.70.
- 60” wide black speaker cloth. Source Jo-Ann. Cost: 1 yd @ $6.80/yd = $6.80.
- miscellaneous (nails, glue, sandpaper, etc) $0.50.

Total cost per absorber = $33. This includes some waste as could only buy the molding in 8’ lengths.

Total time per absorber (once in production mode & not counting time for glue to dry !) approx 2 – 3 hrs. So, I probably spent less time making them than reading about how to make them plus the multiple trips to various stores buy materials :eek:.

Observations & tips:

- Top and bottom frames were laid out on a sheet of 3/4” MDF to provide a nice flat surface as the glue set. Didn’t have any significant problems with warping.

- I mitred the top frames and made them out of “shoe” moulding to provide a nice “rounded” appearance. The rounding was hard to actually notice once the black grill cloth was on the frame. Despite this, and the fact that this approach requires twice as many cuts, I still think it was worth the extra effort.

- All cuts were made by hand using a 16 point dovetail saw and mitre box. All lengths were marked using pre-cut wood pieces rather than a tape measure. This really helped speed & consistency.

- Added 1/4” clearance for fiberglass so that total outside dimensions were 49 3/4” * 25 3/4” * 3 1/8”.

- Didn’t bother painting the wood. The bare frames and the (yellow) fiberglass are not visible through the speaker cloth.

- I was pleased with the way the finished absorbers turns out. Not too obvious that they are DIY. The 3/4" * 1/2" hemlock provided a nice balance between rigidity and weight (although something a bit beefier would be required for frames any larger than these).

Hope the above is useful to other would-be DIY’ers and thanks to other contributors to this thread

Brent

Felgar

09-28-06, 10:51 AM

Wow Brent, looks terrific. I think the rounded edges are a great touch. I only have 2 questions:

1) How are you planning on mounting them to the wall?

2) Did your rigid foam have a paper backing like 703 does? If so, what did you do with it?

kiwishred

09-28-06, 11:40 AM

Felgar - Thanks for the comments. I guess the edges could also be rounded with a router. Problem is, I don't own one.

This is a works in progress so mounting has not yet been determined ;). First thought is to just hang them over a couple of nails that are 5/8" proud of the wall. Nails would fit in gap between upper horizontal cross piece and fiberglass. The heads of the nails would provide a lip to help stop them falling off. However, these things are fairly light (or more accurately, have a high surface area to weight ratio) so I am not all that concerned about what would happen if they fell of the wall. Would be more of a "thud" than a "crash". The alterative would be to make little flat plate hangers, or perhaps use a short length of chain (anything that is an inch or so long and has a couple of holes) that could be screwed into both the frame and wall.

I am yet undecided if I am going to put some sort of cloth backing on the these. Once on the wall, the fiberglass cannot fall out. And the fibers seem fairly well bonded......

The rigid fiberglass I used was "unfaced". 703 is for sure available unfaced as well.

Brent

PYD

09-28-06, 06:59 PM

I am just starting planning after months of reading. I have a room 22x22x10. (I know square is not good). Do I need to build 2x4 walls with GG and two layers of sheetrock or will the 12" cement walls keep sound from traveling. This room is under a garage with an 10" slab. Only one entry door and three sides totally underground and one side into the rest of the house. Was thinking I could just put strapping on walls and not sheetrock? Will this work or do I need to frame walls? Thanks

TAllen01

09-29-06, 10:32 AM

I am on going to buy 1" Linacoustic to line the lower half of my side and front walls. I finally found it locally. I will have some left over. Can I make panels out of this (stuffing it into frames), instead of buying rigid fiberglas panels (which I am having a heck of a time finding locally)? Just trying to save cost, and to use what I have. Also, how is everyone dealing with with outlets once you mount and cover the Linacoustic? Cut holes in Linacoustic and cloth cover, and then extend the outlets 1" from the drywall? With speaker wires, RCA outs, and electric outlets, I'm not sure it will look right (e.g., nice and flat). Any thoughts on how to deal with this issue?

texas teacher

09-30-06, 02:33 AM

Ya'll seem pretty detailed. What's wrong with a little Quietrock sheetrock on the walls and Quietwood on the floors? Seems a lot simpler.

patrickjherbert

09-30-06, 01:58 PM

Let me start by saying that it is a little intimidating entering a thread where some of the participants are clearly experts in their field, and are willing to go to great lengths in the pursuit of perfection. I've been plowing through this thread a little at a time over the last couple of months while in the planning stages for the re-do of my basement, and would like to get your opinions on getting the maybe 85-90% of perfection that I think should be realistically and easily achievable in my circumstance.

I'm dealing with a typical tri-level basement, not very large with ceilings that are about 7'6" when finished. This will be a VERY mixed use room - more than a dedicated home theater. In fact, I will probably do more (casual to serious) music listening than movie watching. I'm building a bar at one end and shoe-horning in a 7' pool table next to that. There will be a number of compromises as a result of everything we are attempting to do, but my goal is to achieve the best acoustic response I can, with the greatest range of usability for the room.

This room had been "finished" by the former owner of the house, and I first had to undo pretty much everything they did. So far I've torn down the sheetrock (which never had the seams taped,) reframed most of the walls (which had stud spacing anywhere from 12" to 20" on center as the mood struck,) and redone the electrical (which could have burned down the house.)

At the end of this post is my hand drawn sketch of the room. Sorry, but I haven't had time to work on this project more than 1 1/2 days a week on average, and I didn't want to spend a couple of days trying to figure out how to use SketchUp.

I'm going to put R-13 behind the drywall and in the ceiling, and was going to put 2" OC 703 behind the stage area. OC 703 superchunks in all four corners (above and below the two rear corner speakers.) I know that putting the rear surrounds in the corners is not optimum, but windows, the pool table, and other space considerations make that compromise necessary. Ditto for the side surrounds.

Finally, my thought was to cover the bottom 40” or so of the right side wall and rear wall with fabric we have picked out that is fairly heavy and passes about 50% of the acoustically transparent “breath test.” Behind the fabric would be 2” OC 703 for a padded wall effect. On the left side of the room there is almost no available space for doing the padded wall thing.

I was thinking that using 2” 703 on the side and rear wall instead of the 1” that seems to be more the norm on these forums would make up for the lack of 703 on the left wall. In the end I decided to “ask for informed directions” before I got too carried away with my assumptions.

Thanks in advance for all the time and information you all share with these groups. Immediately after this post I’ll post a panoramic picture of this space as it looked last week, taken from the bottom left corner of the sketch.
http://home.comcast.net/~patrickjherbert/basement_layout_resized.jpg

patrickjherbert

09-30-06, 02:04 PM

Here is a panoramic shot of the carnage so far. This picture was shot
from the back corner of the bar (lower left-hand corner in the diagram.)
That big empty space on the left side will be a 90 gallon saltwater reef tank someday.

The wall studs are not really crooked, that and some "ghostly" tools are from the stitching program I use.
A seven foot (bar size) pool table will be going to the right of the
bar, and a curved leather sectional sofa will be in front of the Plasma, angled slightly towards the upper right-hand corner of the room.

Don't laugh, you should have seen this room a week ago!

http://home.comcast.net/~patrickjherbert/Basement_panorama_resized.jpg

Terry Montlick

09-30-06, 02:50 PM

Ya'll seem pretty detailed. What's wrong with a little Quietrock sheetrock on the walls and Quietwood on the floors? Seems a lot simpler.
These products are used for sound isolation -- to make your room quiter, and allow less sound to escape to other rooms. They do not improve in-room acoustics, as do absorber panels and other sound treatments. You need both. Sorry that it is even more complicated. :(

Oh, and for sound isolation, you can't just do one part of a room, because sound will happily travel right through the areas you haven't done. So a "little Quietrock sheetrock" becomes "a lot" -- enough for all your wall surfaces and ceiling.

Regards,
Terry

eugovector

10-09-06, 04:10 PM

I've put up some pics and diagrams of my project and have several questions about Positioning Acoustic Panels in an Apartment. I could really use some of the brainpower in this thread. Thanks in advance.

Please comment in this thread:
http://www.avsforum.com/avs-vb/showthread.php?t=734181

TumaraBaap

10-10-06, 02:31 AM

Let me start by saying that it is a little intimidating entering a thread where some of the participants are clearly experts in their field, and are willing to go to great lengths in the pursuit of perfection.

Sometimes I think the thread ought to be unstickied. Many views expressed at the beginning by some of the "experts" have probably evolved considerably. The use of absorption for one is over rated in this thread. (And absorption that defies room symmetry has thankfully never been highly rated.)

Firstly, one is no way NEAR perfection in terms of acoustics if the loudspeaker being used is shoddy. Clearly enthusiasts ought to be demanding better but the infatuation with loudspeakers featuring primitive easily saturated passive crossovers continues. There are indeed very few consumer loudspeakers with the requisite on and off axis flat frequency response.

Once you start with a superb loudspeaker, it's better to optimize reflection and diffusion in the horizontal plane. Early reflections can aid musicality and speech intelligibility. Diffusion affords an enveloping passive surround that complements active surround of multichannel setups. Screw the linacoustic. Any absorption, reflection or diffusion ought to be as broad in bandwidth as possible lest it unbalance the off axis prowess of the loudspeaker being used. Whereas reflections may work laterally, the front and rear reflections are best attenuated or diffused (the latter preferred with adequate distance from diffusor -quadratic residue or prime root- to listening seat). Bass distortion is the worst offender in typical rooms and the ceiling/or wall ceiling corners is a strategic choice for broadband bass traps. The rest of the ceiling can be interspersed with broadband diffusion and absorption. Tortuous calculation of reverberation times is hogwash. With a treated ceiling and furniture, one may already have enough absorption to get away with hardwood floors and area rugs. The Welti/Toole configuration of multiple subs and parametric eq of peaks below 300 Hz should round out amelioration of bass distortion not fixed by broadband bass traps and drywall flex.

Most of this is a far cry from the linacoustic loving advice you'll find in this thread. Balance out whatever advice you typically would get here with what Richard Bird, Russ Berger, John Storyk, or Floyd Toole would advocate (even though they're not always right). Google away.
Tumara Baap

Ethan Winer

10-10-06, 02:05 PM

Tumara,

That's a great post and I agree with almost everything you said. I too don't understand why this was even made a sticky in the first place. It's way too much for anyone to digest, it's full of contradictory and often wrong opinions, and the signal to noise ratio is low.

> enthusiasts ought to be demanding better but the infatuation with loudspeakers featuring primitive easily saturated passive crossovers continues. <

Indeed. And you don't have to pay an arm and a leg for excellent speakers.

> Early reflections can aid musicality and speech intelligibility. <

I read that in Dr. Toole's paper but I disagree. Even Dr. Toole left that "conclusion" open to interpretation. We can continue that in another thread if you'd like to start one.

> Tortuous calculation of reverberation times is hogwash. <

Agreed 100 percent. Most domestic size rooms don't even have reverb.

--Ethan

ciotime

10-11-06, 12:47 AM

pepar

10-11-06, 09:38 AM

Are stages and risers in HT rooms bolted/nailed/screwed to the floor? I would think that they're not so as to decouple them from the floor. But in so doing arent the stage and riser susceptible to movement considering that its not attached to anything? Also is it ok if I only put sand only for the stage where the speakers and sub will be and insulation inside the risers?
FWIW, my riser is not attached to te floor, but it is of sufficient weight that it might as well be. And my LZBoys, feet cradled in "channels," are held only by gravity as well. I constricted the outer frame of the riser from 2 x 12's and the cross members from 2 x 10's effectively suspending the top. I had done this thinking thAt I might add a bass transducer at some point in the future, but it resonates on it's own at around 25Hz so nicely that no active driver is required. Check my link and navigate to the appropriate page to see how I did it.

pepar

10-11-06, 09:51 AM

> Early reflections can aid musicality and speech intelligibility. <

I read that in Dr. Toole's paper but I disagree. Even Dr. Toole left that "conclusion" open to interpretation. We can continue that in another thread if you'd like to start one.

> Tortuous calculation of reverberation times is hogwash. <

Agreed 100 percent. Most domestic size rooms don't even have reverb.

--Ethan
I've experienced the exacty opposite with absorbers at the first reflection points - ALL first reflection points - making a HUGE difference in the intelligibility of music and speech. Which brings me to agreeing that many diverse, and diametrically opposed, opinions being expressed here by seemingly educated and well-meaning individuals so that confusion reigns - at least in my head.

I know I need to control bass peaks resonances in my 13 x 21 x 8 room, but am I now to believe that decay is not important because I don't have any reverb? Should I try to add some? Too dry is no good - I've read that 300 milliseconds is a good target for midband. :confused:

Ethan Winer

10-11-06, 10:42 AM

pepar,

I think your "I came, saw, got drunk" sig is having an effect. :D I can't tell which side you're taking here:

> I've experienced the exacty opposite with absorbers at the first reflection points - ALL first reflection points - making a HUGE difference in the intelligibility of music and speech. <

I'll take it you agree that adding absorption helps intelligibility? That's sure been my experience and the experience of every single person I've ever helped. The text below is from a post I made elsewhere not long ago. (Sadly, those who could not stand to hear opinions that contradict their beliefs locked the thread...)

> am I now to believe that decay is not important because I don't have any reverb? <

A room that size still has "decay" issues that need to be addressed. Besides modal ringing which is tamed with bass traps, there are also first reflections. The difference between decay in a small room and real reverb is more of a technical distinction.

--Ethan

Floyd is brilliant and I agree with most of what he wrote. I enjoyed the article tremendously, and learned a lot too. I hope to read it again at least once if not twice.

Perhaps the most important thing I learned is that "Generic 'good' listening room ratios are a myth" for which he makes a compelling argument. However, his point does not seem to apply for a playback system having bass management if the subwoofer is in a corner, as in my living room HT. I never experimented with four subs, one in each corner, but I suspect the same thing applies there too. If all the modes are activated equally, their ratio should indeed still matter.

I did find a few more things to comment on. In the opening Floyd wrote:

At low frequencies the long-standing problem of room resonances can be alleviated substantially through the use of multiple subwoofers, thereby providing similarly good bass to several listeners in a room.

If you define "good bass" as a flat response, I agree that multiple subs can help. But that does nothing to reduce modal ringing which is at least as damaging as a skewed response, so having multiple subs is not a complete solution. I'm still waiting for proof that modal ringing can be reduced by EQ for an area larger than one cubic inch.

I also think his comparison of music in a concert hall in the context of why we don't mind longer reverb decays is flawed. That's fine for opera and symphony concerts, but it's not relevant for pop music or jazz where the bass instruments are recorded either direct or with a microphone very close. In that case you do not want excess ringing or decay because bass notes can run together losing clarity and articulation.

Likewise, he seems to equate "good" but very late reflections in a concert hall that make the orchestra appear wider than it is, to side wall reflections in a home listening room. This defies my own experience, where absorbing those reflections makes the sound stage wider, rather than the other way around.

Strong directional features were associated with early reflections.

Sure, and this returns us to whether the listening room should impart its own character onto the playback, versus all desired ambience is already in the recording so the room should add nothing further. The latter approach is the only way a recording can be heard as intended in different rooms. I contend that all needed and desired localization is (or should be) already present in the recording through the use of panning and reverb and ambience effects added by the mix engineer.

All of this is clearly relevant to localizing the real sources - the loudspeakers. However, success in doing this may run counter the objectives of music and film sound, which is often to "transport" listeners to other spaces.

Exactly. In a listening room you do not want to localize the sound as coming from the loudspeakers. Untamed reflections defeat this goal. It is very easy to demonstrate that in my own living room, and I do this all the time for visitors. If you stand behind the couch outside the Reflection-Free Zone you can clearly identify the speakers as the sound source. If you then lean forward over the couch the sound stage opens up, becomes wider, and you no longer hear the speakers as the source. (Except maybe for instruments panned all the way left or right.)

Another thing he seems to miss is why a small room seems to sound better than the measurements would imply. As I see it, the reason we can enjoy music in a room that measures excessive comb filtering is because the comb filtering is very different for each ear. He keeps trying to make it sound like the brain is some mysterious processor that is able to make sense of sound even when the comb filtering response is so poor. As Occam would say, I have a simpler explanation: The frequencies missing in one ear due to comb filtering are mostly present in the other ear simply because the ears are far enough apart. Later in the article Floyd seems to recognize this because he observed:

Gilford ... concluded: "The fact that the listening room does not have a predominant effect on quality is very largely due to the binaural mechanism." ... we measure differences that we seem not to hear.

Were we to measure at two locations six inches apart (ear spacing) and combine the results, I believe that would more closely resemble what we hear.

pepar

10-11-06, 12:26 PM

pepar,

I think your "I came, saw, got drunk" sig is having an effect. :D I can't tell which side you're taking here:
:)

> I've experienced the exacty opposite with absorbers at the first reflection points - ALL first reflection points - making a HUGE difference in the intelligibility of music and speech. <

I'll take it you agree that adding absorption helps intelligibility? That's sure been my experience and the experience of every single person I've ever helped. The text below is from a post I made elsewhere not long ago. (Sadly, those who could not stand to hear opinions that contradict their beliefs locked the thread...)
On this, I'm on your "side." :)

> am I now to believe that decay is not important because I don't have any reverb? <

A room that size still has "decay" issues that need to be addressed. Besides modal ringing which is tamed with bass traps, there are also first reflections. The difference between decay in a small room and real reverb is more of a technical distinction.
I'm not sure about the side on this one because I am still a bit confused on the terminology. Does not a room with "decay issues" have a "reverb" problem?

KERMIE

10-11-06, 02:39 PM

How do you handle First Reflection points for Surrounds and rear (Dipole). Are they not suppose to follow the wall a little?

Or should you address these with some treatment?

Thank you

pepar

10-11-06, 03:03 PM

How do you handle First Reflection points for Surrounds and rear (Dipole). Are they not suppose to follow the wall a little?

Or should you address these with some treatment?

Thank you
I think dipole surrounds are supposed to reflect from the surrounding surfaces to develop the soundfields.

KERMIE

10-11-06, 07:38 PM

pepar

10-11-06, 09:17 PM

So if I have a 13 foot wide room and 24 " face base traps in each of the back corners (Floor to Ceiling) it will leave me about 10 feet for a flat back wall. If the rear speakers are on the back wall about 5-6 feet apart will there be enough room between the outside driver of the dipoles shooting towards the base trap. (approx 2 feet from base trap)

thank for the help.
I like dipole surrounds in a 5.1 system to be on the sides for movies. If I listened more to music I'd rather have monopole (or tripole) speakers in the back.

I'm pretty sure I didn't (directly) answer your question. How far from the rear wall is you back row of seats?

TumaraBaap

10-12-06, 01:28 AM

I consider Ethan an authority, and his views are duly noted. In any case, I recommend anyone on an acoustics forum to read Toole's paper for themselves: Loudspeakers and Rooms for Sound Reproduction - A Scientific Review, J. Audio Eng. Soc., Vol.54, No.6, June 2006. This paper is excellent and will prove to be seminal for years to come.

Toole does not upend the conventional wisdom for using side wall absorption; to lock an image in place. If anything, he and Olive have demonstrated in earlier studies how varying the amplitude and delay of lateral reflections affects our perception of spaciousness and image shifting and spreading. He further allows room for standards of reflection control to be developed for multichannel configurations. That said, the paper is unequivocal in enthusing about early lateral reflections.

"Persuasive evidence points to several beneficial and few negative effects of early reflections" ... "Multiple reflections improve the audibility of timbral cues from resonances in the structure of musical and vocal sounds" ... "Early reflections improve speech intelligibility" ... "Early lateral reflections increase our preference for the sound of music and speech. Individual reflections in small rooms may be too low in level to have the optimum effect, thus providing opportunities for multichannel sound"

A notable caveat: Toole insists that for the precedence effect (whereby the brain correctly localizes a sound source in the wake of strong early reflections) to work, the tonality of the direct and reflected sounds should be very close. "If the spectrum of a reflection is different from that of the direct sound, the probability that it will be heard as a separate spatial event is increased - not a good thing." In that case, for most audiophiles with their allegedly cool loudspeakers, the drawl of an Alabama Sheriff upon meeting up with a wrongdoer ought to apply; "Tell you what son, yo ass is s*** outa luck!" They are better off sticking with OC 703 and calling it a day. I might point out that Toole's findings seems to be in line with the observations of those who have designed (or reviewed) highly accurate systems with an excellent polar response, such as teams behind DEQX/ NHT Xd, Seigfried Linkwitz and his Orion, and above all my guru Peter Aczel.

Frankly, I'm not technically inclined enough to argue the merits or otherwise of early reflections in small rooms. I just wanted to give fellow enthusiasts a glimpse of what's in the paper and strongly urge them to read it themselves. As always, I'm in utter awe of Toole's scientific flair. He ruffles many an arbitrary belief, and boy isn't that a lot of fun. :)

Tumara Baap

KERMIE

10-12-06, 02:44 AM

Pepar, my rear speakers will be about 6 feet from the back of the seating area about 1.5 -2 feet above the ears. The same height as the sides.

So if you can picture the back wall like I tried to describe firing about 2 feet from a corner base trap on each of the outside drivers. and about 6 feet apart (inside driver) from each other mounted on the back wall.

I will probably not do anything with that drywall that the speakers will be mounted two but just had some concerns on the outside drivers and the corner base trap.

TumaraBaap, I will look into that......thanks

Schwingding

10-12-06, 06:43 AM

"Flabbergasted" is what I'd like to title this post.

This is probably my first post in this thread/forum. I'm still in reading and learning mode, but have digested enough info that I'm ready to tackle accoustic treatments in my new basement/HT room.

I've spent the last 3 days calling every local (Baltimore) insulation provider listed, and most of the "Home Theater" installers, too, searching for a source of OC703/705. What have I succeeded in? NOTHING. What have I learned? I have learned that there is a shocking lack of knowledge and experience in room treatments. A good 1/2 of the "HT installers" I spoke to don't do anything with regards to room treatments. A salesmen at the local Tweeter was completely in the dark, and most of the insulation supply houses don't carry it or want to sell me something completely unsuitable for the application. They all think I want to "soundproof" a room. In short, you guys are making me look like I'm the one who's nuts! :)

I could buy OC703, oh sure, if I wanted to order a truckload. I need about 30 sheets. So, until I find a suitable local supply, (help anyone? please?) I've had to order it off of the internet, which cannot be anywhere near cost effective.

Flabbergasted. But I'm sure its worth it. You should hear my new 20'x25' room with its bare walls, YIKES! Eww!

Thanks for letting me get that out there. I feel much better.

MarkMac

10-12-06, 08:45 AM

I could buy OC703, oh sure, if I wanted to order a truckload. I need about 30 sheets. So, until I find a suitable local supply, (help anyone? please?) I've had to order it off of the internet, which cannot be anywhere near cost effective.

Schwingding-
I had similar issues until I found SPI. I'm not sure what the closest location is to you (Lancaster, PA?), but I was able to get boxes (24sheets) of 2x4 OC703 1" for ~$80. 45cents/sq.ft. was better than any other price I found.

You may want to look into that:
http://www.spi-co.com/servicecenterdirectory.cfm

Schwingding

10-12-06, 10:07 AM

Schwingding-
I had similar issues until I found SPI. I'm not sure what the closest location is to you (Lancaster, PA?), but I was able to get boxes (24sheets) of 2x4 OC703 1" for ~$80. 45cents/sq.ft. was better than any other price I found.

You may want to look into that:
http://www.spi-co.com/servicecenterdirectory.cfm

That link should be in a master list of references! One call to the Lancaster office and I was speaking with Rick Remington, who proved extremely knowledgable, friendly, and willing to help out on a small homeowner sized requirement. You just made my day, thank you!

pepar

10-12-06, 10:15 AM

Pepar, my rear speakers will be about 6 feet from the back of the seating area about 1.5 -2 feet above the ears. The same height as the sides.
Sooo, this is a 7.1 system?

Felgar

10-12-06, 10:47 AM

A notable caveat: Toole insists that for the precedence effect (whereby the brain correctly localizes a sound source in the wake of strong early reflections) to work, the tonality of the direct and reflected sounds should be very close. "If the spectrum of a reflection is different from that of the direct sound, the probability that it will be heard as a separate spatial event is increased - not a good thing." In that case, for most audiophiles with their allegedly cool loudspeakers, the drawl of an Alabama Sheriff upon meeting up with a wrongdoer ought to apply; "Tell you what son, yo ass is s*** outa luck!" They are better off sticking with OC 703 and calling it a day.
It seems ludricrous to me to think that for the sound reflected off a sheet of drywall, the wall itself would have little to no effect on the tonal characteristics of the sound. The wall is not perfectly smooth and will also vibrate, thus adding it's own sound to the reflected sound. Even differing wall constructions will yield different behaviour so I don't see how the reflected sound could be considered close to accurate. The ceiling is probably even worse, suffering from (typically) less accurate vertical off-axis dispersion of the speaker and a surface that's not nearly as smooth with a typical stippled construction.

pepar

10-12-06, 10:54 AM

KERMIE

10-12-06, 11:14 AM

eugovector

10-12-06, 01:28 PM

That link should be in a master list of references! One call to the Lancaster office and I was speaking with Rick Remington, who proved extremely knowledgable, friendly, and willing to help out on a small homeowner sized requirement. You just made my day, thank you!

So how much did everything cost, does he ship?

I went with ejdavis.com, based in CT, who shipped 2" unfaced 703 in cartons of 6. I bought 12 2x4 sheets @ 77 cents/sqft. Shipped in 2 boxes, my total was $118.94.

ejdavis was a much better price than I found anywhere else, and though I can't afford any more right now, I'll probably be building some more panels in the future. So far, simply putting a single panel at the first refelction points on my left and right walls produced a noticably more clarity in center channel dialogue. I've started recommending this to everyone,and by far the most complicated part of the whole process is finding 703 at a decent price.

Ethan Winer

10-12-06, 03:41 PM

pepar,

> Does not a room with "decay issues" have a "reverb" problem? <

It depends on the size of the room. Smaller rooms have only modal ringing, where the extended decays are highly frequency selective. A large space, like a gymnasium or auditorium, has true reverb, where you can play 100 Hz or 101 Hz or 97 Hz and have similar decay times at all those frequencies. Medium size rooms fall somewhere in between. As I understand it, to be considered true reverb the sound must first swell over time, during which more and more reflections combine to create a coherent "haaah" sound. As opposed to the modal ringing and discrete "ping" and "boing" echoes you get in smaller spaces.

--Ethan

pepar

10-12-06, 06:34 PM

Yes it is 7.1,

so basically I would have 1 side of each of the 4 dipole surrounds firing towards a Corner Base trap. I see this a lot on some of these theaters but what effect does that have on Dipole for surrounds.
OK, my preference is to use monopoles for the rears in a 7.1. If your's are not adjustable, I would suggest moving them a wee bit closer together. As there are no discrete rear channels (yet) you will not be losing any separation. And you'll probably generate a more enveloping rear soundfield by hetting them away from your traps.

Just my $.01, $.02 or $.03.

pepar

10-12-06, 06:35 PM

TumaraBaap

10-13-06, 02:02 AM

It seems ludricrous to me to think that for the sound reflected off a sheet of drywall, the wall itself would have little to no effect on the tonal characteristics of the sound. The wall is not perfectly smooth and will also vibrate, thus adding it's own sound to the reflected sound. Even differing wall constructions will yield different behaviour so I don't see how the reflected sound could be considered close to accurate. The ceiling is probably even worse, suffering from (typically) less accurate vertical off-axis dispersion of the speaker and a surface that's not nearly as smooth with a typical stippled construction.

Those reflections apply to frequencies above the schroeder/transition frequency where the drywall would be more or less uniformly reflective. Below the transition frequency, drywall flex actually aids modal issues. Any texturing of the typical wall would only affect frequencies way above 20KHz. Rest assured, there is absolutely no need to be looking into a smooth as glass concrete wall. As for vertical off axis problems, you're on top of things. Hence the operative word "lateral" when speaking of the beneficial early reflection in question.
Tumara Baap

Felgar

10-13-06, 10:34 AM

Well, thanks for sharing Tumara. If nothing else I'll be sure to keep an open mind and A/B with and without treatments on my first reflection points.

pepar

10-13-06, 11:14 AM

Well, thanks for sharing Tumara. If nothing else I'll be sure to keep an open mind and A/B with and without treatments on my first reflection points.
The first absorber - 2" OC Selectsound Black - I placed at a first reflection point was the REAR wall, a surface that sometimes gets overlooked by us layman. The difference was ASTONISHING - improvements in clarity, main/surround integration and somewhat tightened bottom. The next surfaces I treated were left and right front walls. This produced an incremental improvement in clarity and main/surround integration. The final surface treated was the front ceiling. This made a larger improvement in the aforementioned areas than the side wall treatment, but not as great as the rear wall did.

Just my $.01, $.02 or $.03.

KERMIE

10-13-06, 11:57 AM

So on my back wall, which will be about 14-15 feet away from my Front speakers, should I use some sort of diffusion panels? if I keep it away from my rears (like above or below)?

pepar

10-13-06, 12:02 PM

So on my back wall, which will be about 14-15 feet away from my Front speakers, should I use some sort of diffusion panels? if I keep it away from my rears (like above or below)?
I used absorption. Others recommend diffusion, and I might give that a try myself - just to see the effect. If you used diffusion, you would (probably) not need to worry about it's proximity to your surrounds.

Ron Jones

10-13-06, 12:32 PM

For item (a) I don't understand what is being implied by the "polyester batting above". Where and how is the polyester batting used?

Ron Jones

Felgar

10-13-06, 01:47 PM

The first absorber - 2" OC Selectsound Black - I placed at a first reflection point was the REAR wall, a surface that sometimes gets overlooked by us layman. The difference was ASTONISHING - improvements in clarity, main/surround integration and somewhat tightened bottom. The next surfaces I treated were left and right front walls. This produced an incremental improvement in clarity and main/surround integration. The final surface treated was the front ceiling. This made a larger improvement in the aforementioned areas than the side wall treatment, but not as great as the rear wall did.
Wow, thanks for the tip. I was thinking to target the sides first and go from there but this is interesting food for thought. In my case the main LP will be a home theatre recliner at front-center, and behind that will be a leather sofa on a 12" riser. I expect the reflection point to be the lower portion of the back of the sofa. So hopefully the sofa behaves better than a wall in terms of absorbtion and reflection. It will probably reflect high frequencies a fair amount; I guess I'll play around to see if buying a cloth sofa would make a substantial difference in SQ...

eugovector

10-13-06, 02:26 PM

Wow, thanks for the tip. I was thinking to target the sides first and go from there but this is interesting food for thought. In my case the main LP will be a home theatre recliner at front-center, and behind that will be a leather sofa on a 12" riser. I expect the reflection point to be the lower portion of the back of the sofa. So hopefully the sofa behaves better than a wall in terms of absorbtion and reflection. It will probably reflect high frequencies a fair amount; I guess I'll play around to see if buying a cloth sofa would make a substantial difference in SQ...

I had the same results, but did the sides first. Based on my temp placement so far, I'd say you should do sides, back, and ceiling.

Instead of buying a cloth sofa, how about just putting a think blanket over the back of the leather one?

chillinintheoc

10-15-06, 03:11 AM

Im getting ready to put the 1" Linacoustic RC on my walls....is there a front and back to this stuff?
What part do I put agents the wall?
And what is the best thing to use for your 1" Furring strips?

Thanks
Chillinintheoc

bpape

10-16-06, 12:25 AM

Ron.

The batting is used on the upper half of the walls to fill in behind the GOM to the same level as the Linacoustic below. If you don't want the extra HF absorbtion you can use something inert like styrofoam that will not absorb anything but will provide a more solid backing.

Chillin,

Use the side with the coating on it out toward the room. You'll have to rip the 1" strips yourself - or spend a lot of money buying craft lumber.

Bryan

Stima

10-16-06, 01:20 AM

Ron.

The batting is used on the upper half of the walls to fill in behind the GOM to the same level as the Linacoustic below. If you don't want the extra HF absorption you can use something inert like Styrofoam that will not absorb anything but will provide a more solid backing.

Damn it...had a nice thought out response as to why I hate my batting...and then I hit the wrong button and it all disappeared. :mad:

So, long story short....I hate my batting above my OC701 so much so I actually considered tearing down all my GOM and wood work to replace the batting with wood, drywall or even Styrofoam as Bryan suggests. I found it impossible to get the batting to lay perfectly smooth as it does over the fiberglass. The fiberglass fibers hold the GOM nice and smooth while the batting causes it to "poof" out.

Anyway, do what you want...but the very very small amount of high freq. absorption afforded by the batting is FAR outweighed by the PITA poofy factor. (IMHO)

Stima

10-16-06, 01:33 AM

Use the side with the coating on it out toward the room. You'll have to rip the 1" strips yourself - or spend a lot of money buying craft lumber.

Bryan

I went a different route than the above suggestions:

I looked around my local Home Depot and of course didn't find any wood that was perfect for 1" tall firring strips. However, I DID find some .75" tall pine and some .25" tall pine that stacked up to be the perfect height. Now, while I could have bought the exact same length for each material...I went the even MORE economical route of cutting the .25" stripes into 2" long "spacers". I simply nailed\screwed the .75" strips to the wall every foot or so with a spacer between it and the wall. I found I had to pre-drill holes in the spacers to keep them from cracking, but it worked very well. I pretty much only air-nailed\screwed at the wall studs. If I had a piece of firring that didn't line up on a stud, I used cheap drywall hangers (the plastic butterfly things that expand when you screw into them). This took a little extra time to put in the hangers, but I probably saved 50$ in wood. In either case, I would have had to use drywall hangers for some short firring pieces around outlets and at the riser steps.

To get a better idea here are a few pics of my room. Every where you see brown trim, there is firring strips behind the trim. This allowed my to make a pattern with my GOM and NOT have ANY visible seams. The GOM on each wall is a single continuous piece. FYI: I used outlet covers to hide the staples around the outlets along with small pieces of window molding under my soffits to hide staples and generic floor board molding at the floor. (It was all generic pine I stained.)

Front:
http://i21.photobucket.com/albums/b262/dstima/DSC00072.jpg

Back:
http://i21.photobucket.com/albums/b262/dstima/DSC00064.jpg

pepar

10-16-06, 07:59 AM

Stima, do you not find you get a lot of light reflecting off of the light surfaces, especially the ceiling, that washes out the projected image on the screen?

Stima

10-17-06, 01:05 AM

I do see some light reflecting off the ceiling and walls, but it does not deter the picture any that I can see.

I will take a picture of a paused movie with a wide angle lens and post it back.

edit: added pictures and modified above sentence regarding reflected light.

Didn't level tripod well, but you'll get the idea. Also, chromatic distortion by unicorns head is only seen on camera, not on screen. :(

Sony DSC-H5 F3.5, 1/2 sec, ISO-125
http://i21.photobucket.com/albums/b262/dstima/DSC00448.jpg

Sony DSC-H5 F3.5 1/6 sec, ISO-125
Zoomed to show lack of "wash out"
http://i21.photobucket.com/albums/b262/dstima/DSC00450.jpg

TAllen01

10-17-06, 09:16 AM

eugovector

10-17-06, 09:40 AM

I agree with some of the posts from last week. We need a sticky for "where to buy" DIY materials for acoustic treatments.

There's one here: Ethan's Forum (http://www.musicplayer.com/cgi-bin/ultimatebb.cgi?/ubb/forum/f/26.html)

pepar

10-17-06, 09:44 AM

I agree with some of the posts from last week. We need a sticky for "where to buy" DIY materials for acoustic treatments. I, like many others, called high and low and spent hours drvingin around trying to find OC 703 or Johns Manville stuff at the Do It Best stores, HD, Lowes, etc. I finally found it by going to the spi website after reading one thread from someone building a theater in my neck of the woods. Once I found them, I made one call and went to pick up as much as I needed. It was all in-stock, 15 miles away, but SOOO hard to find them. I ended up getting a 1.5" thick, Johns-Mansville equivalent to OC 703 for about .80 per square foot near Cincinnati.
These materials can be purchased most economically at an HVAC (Heating Ventilation and Air Conditioning) supplier, but you must find a smaller one unless you need a lot of material or find one who'll accomodate you. I purchased two rolls of J-M Linacoustic at a distributor in the Philly area and three packs of four 4x8 sheets of OC SelectSound Black at a distributor close to MD. When I wanted to buy OC 703, I again priced it at the Balto place, but also found SPI (http://www.spi-co.com/servicecenterdirectory.cfm). Coincidentally, their headquarters is 20 miles from my home. Their price was SO much better than the Balto one that I was insulted! The link is to their service center directory and shows locations all over the country with the highest concentration east of the Mississippi. They carry many brands, have favorable pricing and are the best resource I've run across for acoustical materials.

pepar

10-17-06, 09:48 AM

I do see some light reflecting off the ceiling and walls, but it does not deter the picture any that I can see.
I guess it's a matter of preference - and how easily one is distracted. Personally, the light reflecting off the ceiling and the side walls would distract me too much. I prefer flat black so there is NO light coming at me from anywhere other than the screen.

Stima

10-17-06, 12:16 PM

eugovector

10-17-06, 02:01 PM

The light reflection would probably be more noticeable if the viewing distance to screen diag ratio wasn't so close to 1. (10' wide screen with seating at 12" and 16") :o The picture is just so huge, my eyes just don't ever notice the extra light on the walls and ceiling. :cool:

I'm assuming you meant 12' and 16'. What's your source, don' t you find that too large/close for viewing?

Watching DVDs at a little less than 2 times the screen diagonal, I start to see some softness in the picture.

Stima

10-17-06, 03:42 PM

I'm assuming you meant 12' and 16'. What's your source, don' t you find that too large/close for viewing?

Watching DVDs at a little less than 2 times the screen diagonal, I start to see some softness in the picture.

Yeah, 12' and 16'. I currently am running a InFocus SP4805 with a Panamorph Horizontal Expansion Lens to achieve 2.35:1. Source material is DVD and an old HD OTA receiver for Monday Night Football. I have a media server with DVD rips just itching to be used, but I don't have the cash to purchase a Media Extender that can handle ISO's.

Once I save some more pennies, the FIRST thing I will do is replace the source, projector and lens. I decided to first focus my money on the building of the room and it's audio properties. I can easily upgrade a projector...redoing acoustical treatments on the other hand ain't so easy.

BTW, one of the VERY FEW benefits of poor eyesight is the ability to have a bigger picture and not be able to tell it is soft or pixelated. I have 20/30 and 20/40 vision due to a degenerative eye disease. :o

Now my brother-in-law who has better than 20/20 can see the pixels at 12' but not 16' where I can only see them at a couple feet.

eugovector

10-17-06, 03:45 PM

Yeah, 12' and 16'.

One of the VERY FEW benefits of poor eyesight is the ability to have a bigger picture and not be able to tell it is soft or pixelated. :o

My brother-in-law who has better than 20/20 can see the pixels at 12' but not 16' where I can only see them at a couple feet.

My mom always used to say that sitting to close to the television would give me bad eyesight. I guess with your experience to back that up, I'd better scoot back a couple feet :)

Stima

10-17-06, 03:49 PM

My mom always used to say that sitting to close to the television would give me bad eyesight. I guess with your experience to back that up, I'd better scoot back a couple feet :)

sorry for the edit while you were replying.

Yeah, my problem wasn't sitting to close...rather genetics. My twin brother has also been diagnosied. Sucks for us :(

kjohn

10-19-06, 07:40 PM

I am still trying to under stand about treating the rear wall my room is appox. 13'.5" x 8' x 26' should I put a panel on the rear wall.

eugovector

10-19-06, 07:50 PM

I am still trying to under stand about treating the rear wall my room is appox. 13'.5" x 8' x 26' should I put a panel on the rear wall.

I'm obviously far from an expert, but in my limited experience, I found benefits in treating all first relection points (left, right, front, back, ceiling, floor) for both music and movies.

I'd say yes, at least at 1st reflection points.

pepar

10-19-06, 07:53 PM

I'm obviously far from an expert, but in my limited experience, I found benefits in treating all first relection points (left, right, front, back, ceiling, floor) for both music and movies.

I'd say yes, at least at 1st reflection points.
Treating my back wall made a bigger difference than doing the ceiling or left/right front walls.

myfipie

10-23-06, 10:02 AM

Treating the back wall is going to help with nulls and peaks that you would get off the back wall. Treating the side walls is going to help with imaging of the speakers. So yes you do want to treat the back wall and the side walls. For the back wall it might be best to go with a 4" panel spaced off the wall 4". For the side walls a 2 inch panel should work fine.

Glenn

ciotime

10-23-06, 10:56 AM

pepar

10-23-06, 11:17 AM

When you say treat the back wall do you mean the entire back wall? Coz on a 7.1 setup Ive read a lot of posts' that say to treat only the middle part of the back wall...ie divide the back wall into 3 parts and leave the right/left back wall reflective.
That's good thinking. The rear surrounds, especially if dipole, need reflective surfaces in order to create enveloping soundfields. Determining where *to* treat can be done with the classic "mirror method." I've never used a mirror, but applied the concept by eyeballing. You might be able to visualize it easier if you think of bank shots on a pool table. Angle of incidence = angle of reflection. I've seen some recommending DIFFUSION on the rear wall instead of absorption. With that, one does not need to be concerned about deadening too much rear wall and negatively impacting rear surrounds.

fredpamm

10-23-06, 05:01 PM

Guys I need a little help to understand.

Currently I am building out my basement part of which is a home theater. I am in the drywall stage.

I have a room that is 22'6" by 15'3" with two 45 degree angled walls next to the screen (part of foundation).

Technology includes Yamaha 2600, Panny ae900, Dalite da-snap cinema vision 133 diagonal, klipsch rf5, rs52, rc52 rw12d home theatre, oppo 971 dvd player

I have single walls next to the foundation and double decoupled walls on the sides and back of the HT. The cavities are full of insulation walls and ceiling.

All of this I learned on this web site (thanks so much)

Then I started to read this thread about acoustical treatments.

There are so many opinions that I am not sure what's right or wrong.

My eyes glaze over and I am confused....

Can anyone simply break down for me what is needed in my little corner of the world? I have attached somewhat of a drawing of my theater....

Thanks in advance...

BasementBob

10-23-06, 05:35 PM

myfipie
Treating the back wall is going to help with nulls and peaks that you would get off the back wall. True.

But that's a little like saying the drug digoxin can reduce the ventricular rate of the heart. That is also true, but that doesn't mean that we want to take digoxin all the time.

If the room is large enough and far enough behind the listeners, treating the back wall with absorption might not help at all. In this case the room is 26' long -- which seems to fall into that 'ask more questions' category because the wall is possibly more than 11' behind the listener.

Absorption just isn't something you do. Absorption is a treatment. I'm a big proponent of: Diagnose/describe the problem that needs solving, then treat it.

e.g. Absorption on the rear wall can affect Haas, and/or it can treat a mode, etc. Although the front wall might be better than the rear because the same treatment can also deal with SBIR, and still maintain ambiance. Absorption anywhere can affect RT60, envelopment, as well as the speaker watts required to fill room.

(Side wall reflection taming seems to be good by hugely far most of the time in home theatre. Or to put it another way I'd have to work fairly hard to dream up an example of a in-the-home-theatre where it wasn't the case. Interestingly enough, my living room has a reflection free zone due to the drywall geometry that falls into this category, but it's rare and odd, and unfortunately for me will suffer from other less than optimal problems)

myfipie

10-23-06, 06:56 PM

myfipie
True.

But that's a little like saying the drug digoxin can reduce the ventricular rate of the heart. That is also true, but that doesn't mean that we want to take digoxin all the time.

If the room is large enough and far enough behind the listeners, treating the back wall with absorption might not help at all. In this case the room is 26' long -- which seems to fall into that 'ask more questions' category because the wall is possibly more than 11' behind the listener.

Absorption just isn't something you do. Absorption is a treatment. I'm a big proponent of: Diagnose/describe the problem that needs solving, then treat it.

e.g. Absorption on the rear wall can affect Haas, and/or it can treat a mode, etc. Although the front wall might be better than the rear because the same treatment can also deal with SBIR, and still maintain ambiance. Absorption anywhere can affect RT60, envelopment, as well as the speaker watts required to fill room.

(Side wall reflection taming seems to be good by hugely far most of the time in home theatre. Or to put it another way I'd have to work fairly hard to dream up an example of a in-the-home-theatre where it wasn't the case. Interestingly enough, my living room has a reflection free zone due to the drywall geometry that falls into this category, but it's rare and odd, and unfortunately for me will suffer from other less than optimal problems)

Well said and I would agree. There really is not a "one size" fits all in any of this stuff. We just got back from treating 3 rooms at the RMAF out in denver and all the rooms where the same size. But because of the different speakers we did have to tweak somethings a little different. So it is not only the room but the kind of speakers will matter also.

Glenn

Ethan Winer

10-24-06, 01:17 PM

Fred,

> Can anyone simply break down for me what is needed in my little corner of the world? <

This is a deep subject, and a complete answer requires far more than will fit into a single reply here. The short version is:

* Broadband (not tuned) bass traps straddling as many corners as you can manage, including the wall-ceiling corners.

* Mid/high frequency absorption at the first reflection points on the side walls and ceiling.

* Some additional amount of mid/high absorption on any large areas of bare parallel surfaces, such as opposing walls or the ceiling if the floor is reflective.

For the complete story see my Acoustics FAQ. (www.ethanwiner.com/acoustics.html)

In your case the angled front walls are a problem because they "wall off" one of the best places to put bass traps. But that too can be worked around. For best results you should treat both sets of corners on each side. Also, with seating right up against the rear wall you'll want additional broadband absorption on that wall to avoid the inevitable "early" reflections and comb filtering from that wall.

--Ethan

pepar

10-24-06, 04:00 PM

* Broadband bass traps (absorption)

* Mid/high frequency absorption

* Some additional amount of mid/high absorption

* with seating right up against the rear wall you'll want additional broadband absorption
Has diffusion fallen out of favor? :)

fredpamm

10-24-06, 04:53 PM

Stima

10-24-06, 10:48 PM

Thanks Ethan.

So it sounds to me like some of the OC703/GOM installations that I have seen would handle the angled corners and on the side and back walls. Then put bass traps in the corners...

The floor will be carpet and there is a 12" riser filled with insulation in the back of the room. That should help some, right?

For the riser to be useful as a bass trap, it would need to be tuned through the use of a port (think sub woofer port). Just thinking about it in the simplest of ways...having a solid riser in back will do nothing to help treat bass since the bass can't travel well through the solid mass walls and floor to be properly attenuated. So I would have to say the riser stuffed with insulation will do very little to help the room response.

As far as 703 and GOM. Some would say the front wall needs to be as dead as possible, while others say it should be as live as possible to allow the front speakers to produce the correct ambiance. I personally, went the route of Dennis Erskine's personal suggestions and treated the entire front area floor to ceiling with 703. (I also have a "bay window" foundation cutout behind my screen and front speakers.)

fredpamm

10-25-06, 10:37 AM

Thanks Stima... I appreciate your input....

Ethan Winer

10-25-06, 02:12 PM

Has diffusion fallen out of favor? :)

ROFL. The moment we start shipping, you can bet I'll change my tune.

I'm kidding! :D:D:D

Seriously, there's been a huge amount of interest in our new diffusor, and I'm even getting calls from magazines asking to review them. But when a customer calls and asks, I still explain that absorption is the staple and diffusion is the icing on the cake. Then again, once I load up my own listening room with diffusors to hear them in context properly, maybe I really will change my tune. :eek:

I brought a bunch of traps and "HF" panels to a local potential customer not long ago. He had a really nice setup with RPG classic QRD well diffusors all over the place, including at the first reflection points. The diffusors really did help make the room sound larger, but he ended up buying all of the traps we brought plus two more because they made things even more focused.

--Ethan

Dennis Erskine

10-25-06, 02:50 PM

Actually, the latest research by Toole, Olive, et. al. strongly suggests that diffusion is very much under used and absorption is very much over utilized.

pepar

10-25-06, 03:42 PM

ROFL. The moment we start shipping, you can bet I'll change my tune. :D:D:D
RealDiffusors? ;)

Ethan Winer

10-26-06, 11:46 AM

RealDiffusors? ;)

Yes, I thought that's what you were referring to. We announced a new diffusor last week, and will begin shipping Real Soon Now. In November, anyway.

--Ethan

Stima

10-26-06, 12:06 PM

Please don't take this as anything but a friendly gesture.

I have seen a couple other threads closed due to "sales talk" recently.

I would HATE to see this thread locked for that reason.

Again...I mean NO disrespect to anyone. Just looking out for the greater good! ;)

BasementBob

10-26-06, 01:46 PM

Actually, the latest research by Toole, Olive, et. al. strongly suggests that diffusion is very much under used and absorption is very much over utilized.

I don't know if this is the 'latest', but the below quote is from: "Loudspeakers and Rooms - Working Together" by Floyd E. Toole, Ph.D.

Diffusion refers to the degree of randomness in the directions of arrival of sounds at a point in space. Diffusion in the sound field surrounding a listener in a concert hall is an absolutely essential requirement. It is of some use in home theater rooms. It is of little use in stereo rooms.
In a concert hall, diffusion helps communicate all of the sound from all of the instruments on stage, to all of the listeners in the audience. If there were total diffusion, listeners would not know where the sounds are coming from, so there must be a balance among direct, reflected and diffuse sounds.
In a surround sound application, Dolby ProLogic requires low correlation in the sounds arriving at the ears from the surround channel speakers in order to generate a sense of ambiguous spaciousness. In THX systems, electronic decorrelation in the signals sent to the left and right surrounds helps, and bidirectional out-of-phase “dipole” surround speakers can be of further assistance. The latter is an attempt to increase the diffusion in the sound field. Acoustically “dead” rooms work against that effort, and irregular reflective surfaces and objects in the room work with it. Unfortunately, the front channels really need to “see” a relatively dead room, which creates a dilemma that has not been satisfactorily solved. Dolby Digital / AC-3 and DTS multichannel music call for five identical channels and loudspeakers, thus presumably calling for a relatively dead room. On the other hand, multichannel music might well be better in a normally live room. Then there are systems like Lexicon’s Logic-7 and Citation 6-axis that go directly to the core issue - five channels are not enough. They add channels in the rear of the room. And so it goes. This issue is not settled yet.
Conventional two-channel stereo is another real dilemma. Here loudspeakers range from highly unidirectional through multidirectional to omnidirectional. Each category requires different room treatment and positions. Listener preferences cannot be ignored. Some like a large spacious illusion (a relatively live room), others like pinpoint imaging (a relatively dead room).
A common compromise is to avoid the decision of whether to absorb or to reflect, and opt to diffuse the sound with any one of the several available irregular reflecting devices. A diffuser is an elaborate reflector, in that it sends any incoming sound off in many different directions. This is not a bad idea, and diffusers have an important place in the repertoire of acoustical devices. Just remember that they are still reflectors, and the sound energy is merely redirected. Stereo is a system in which fragile phantom images are an essential part of the illusion. I have been in rooms where many dollars were spent on diffusers which did little more than destroy the stereo image that every other device in the signal path attempted to preserve. One can have too much of a good thing.
A simple test is to reproduce monophonic pink noise at equal levels through both loudspeakers. For a listener on the axis of symmetry, the result should be a compact auditory image midway between the loudspeakers. Moving the head slightly to the left and right should reveal a symmetrical brightening, as the acoustical-cross talk interference is changed, and the stereo axis should "lock in" with great precision.

sdurani

10-26-06, 03:05 PM

Bob, how old is that paper? They still reference old Pro Logic and Citation 6-Axis.

Sanjay

BasementBob

10-26-06, 08:31 PM

sdurani:
Good catch. I thought it was the one I downloaded recently, turns out I downloaded it in 2002, and it was written August 1999. So it's not 'latest'. :)

Dennis Erskine

10-27-06, 09:16 AM

Toole's most recent work is published in the AES library.

pepar

10-27-06, 09:46 AM

Toole's most recent work is published in the AES library.
So, has the thinking changed since '99 on the issues discussed in the paper quoted by Bob?

Terry Montlick

10-27-06, 10:05 AM

Toole's most recent work is published in the AES library.
His latest paper in the June JAES is actually a review article, not new research. But it is an excellent, detailed presentation of his current "stump speech."

I think he is wrong on some implications (he's pushed for his views as far as he reasonably can in a peer-reviewed journal). This is principally because he does not consider the case of movie soundtrack reproduction in any detail. We cannot necessarily lump this together with multichannel music reproduction. Still, his questions are provocative, and when Floyd Toole talks, we listen.

- Terry

pepar

10-27-06, 10:28 AM

Speaking strictly as a layman with only a somewhat educated ear from 40 years of music appreciation and a smattering of live sound reinforcement and studio work, I find the things I knew/thought I knew/assumed about 2-channel reproduction are difficult to reconcile with the 7.1-ness of my current hobby/passion/obsession. While obviously dated, referring to "decorrelation" in THX systems' surrounds when it is now discrete, Bob's Toole quote *does* somewhat address what he considers the needs of the mains vis-a-vis those of the (dipole) surrounds. Perhaps after treating the mains/audience first reflection points with absorption and using a lot of diffusion elsewhere is the way to go. The FRP absorbers would seem to have little effect on sound radiating from the surrounds while the diffusion would help both. Does this make sense at all?

Dennis Erskine

10-27-06, 11:00 AM

when Floyd Toole talks, we listen.
Indeed. :) I'm working on a spectral analysis/measurement problem with Todd and Floyd's input is certainly thought provoking.

Ethan Winer

10-27-06, 01:28 PM

Terry,

> I think he is wrong on some implications ... when Floyd Toole talks, we listen. <

That sums up my feelings too. I don't recall if I posted my "mini review" of Floyd's latest paper here at AVS, so I repeat it again below. This was in response to someone in another forum claiming Floyd "proved" that early reflections are beneficial.

--Ethan

Floyd is brilliant and I agree with most of what he wrote. I enjoyed the article tremendously, and learned a lot too. I hope to read it again at least once if not twice.

Perhaps the most important thing I learned is that "Generic 'good' listening room ratios are a myth" for which he makes a compelling argument. However, his point does not seem to apply for a playback system having bass management if the subwoofer is in a corner, as in my living room HT. I never experimented with four subs, but I suspect the same thing applies there too. If all the modes are activated equally, their ratio should indeed still matter.

I did find a few more things to comment on. In the opening Floyd wrote:

At low frequencies the long-standing problem of room resonances can be alleviated substantially through the use of multiple subwoofers, thereby providing similarly good bass to several listeners in a room.

If you define "good bass" as a flat response, I agree that multiple subs can help. But that does nothing to reduce modal ringing which is at least as damaging as a skewed response, so having multiple subs is not a complete solution. I'm still waiting for proof that modal ringing can be reduced by EQ for an area larger than one cubic inch.

I also think his comparison of music in a concert hall in the context of why we don't mind longer reverb decays is flawed. That's fine for opera and symphony concerts, but it's not relevant for pop music or jazz where the bass instruments are recorded either direct or with a microphone very close. In that case you do not want excess ringing or decay because bass notes can run together losing clarity and articulation.

Likewise, he seems to equate "good" but very late reflections in a concert hall that make the orchestra appear wider than it is, to side wall reflections in a home listening room. This defies my own experience, where absorbing those reflections makes the sound stage wider, rather than the other way around.

Strong directional features were associated with early reflections.

Sure, and this returns us to whether the listening room should impart its own character onto the playback, versus all desired ambience is already in the recording so the room should add nothing further. The latter approach is the only way a recording can be heard as intended in different rooms. I contend that all needed and desired localization is (or should be) already present in the recording through the use of panning and reverb and ambience effects added by the mix engineer.

All of this is clearly relevant to localizing the real sources - the loudspeakers. However, success in doing this may run counter the objectives of music and film sound, which is often to "transport" listeners to other spaces.

Exactly. In a listening room you do not want to localize the sound as coming from the loudspeakers. Untamed reflections defeat this goal. It is very easy to demonstrate that in my own living room, and I do this all the time for visitors. If you stand behind the couch outside the Reflection-Free Zone you can clearly identify the speakers as the sound source. If you then lean forward over the couch the sound stage opens up, becomes wider, and you no longer hear the speakers as the source. (Except maybe for instruments panned all the way left or right.)

Another thing he seems to miss is why a small room seems to sound better than the measurements would imply. As I see it, the reason we can enjoy music in a room that measures excessive comb filtering is because the comb filtering is very different for each ear. He keeps trying to make it sound like the brain is some mysterious processor that is able to make sense of sound even when the comb filtering response is so poor. As Occam would say, I have a simpler explanation: The frequencies missing in one ear due to comb filtering are mostly present in the other ear simply because the ears are far enough apart. Later in the article Floyd seems to recognize this because he observed:

Gilford ... concluded: "The fact that the listening room does not have a predominant effect on quality is very largely due to the binaural mechanism." ... we measure differences that we seem not to hear.

Were we to measure at two locations six inches apart (ear spacing) and combine the results, I believe that would more closely resemble what we hear.

Terry Montlick

10-27-06, 03:48 PM

Terry,
[snip]
... this returns us to whether the listening room should impart its own character onto the playback, versus all desired ambience is already in the recording so the room should add nothing further. The latter approach is the only way a recording can be heard as intended in different rooms. I contend that all needed and desired localization is (or should be) already present in the recording through the use of panning and reverb and ambience effects added by the mix engineer.

Exactly. If you are playing a dry stereo recording of a string quartet and you want it to sound like they are playing right in your livingroom, you want the room to maximally contribute its ambiance. The solution to this was found by Amar Bose, in his invention of the 901 speaker. But today's multichannel recordings require different solutions.

- Terry

Ethan Winer

10-27-06, 04:44 PM

Terry,

> The solution to this was found by Amar Bose, in his invention of the 901 speaker. But today's multichannel recordings require different solutions. <

Not sure I get your points, nor can I even tell if you're agreeing or disagreeing. :D

Bose 901s intentionally bounce sound off the walls to increase the ambience added by the room. So that's the opposite of what I'd recommend. And all string quartet recordings have at least some room/hall sound already in the recording, no? Indeed, I've often thought that a totally dry recording is a great idea because that would finally bring chamber music into the chamber, so to speak, and it really would sound like the players are right there in the room with you. I came "this" close to hiring a pro quartet I know just to do such experiments, but then balked at spending a grand or more on yet another of my pie in the sky ideas. :eek: :D

What I'm talking about is that all recordings already have all the desired ambience in place as decided by the producer and mixing engineer, so the room shouldn't add more of its own ambience. How does that differ from the goal of "today's multichannel recordings?"

One other factor with all this is where you are in the virtual concert hall. I hate being way in the back of a hall because there's more reflected sound than direct sound, and everything sounds like a mushy mess. Even in a really good concert hall. The front row might not always be the best choice either, but in the three local auditoriums I frequent somewhere around the 10th row is pretty good. So if I were mixing a classical CD I'd aim for about that amount of ambience / distance, and hope that the listener's room doesn't wreck that by adding too much of its own "small room" character.

--Ethan

Terry Montlick

10-27-06, 05:21 PM

I'm agreeing. :)

My point was that the acoustical goals in the stereo, Bose 901 days were very different from the goals for current multichannel reproduction.

kiwishred

10-28-06, 06:14 PM

FWIW, if I really want to hear something clearly, for example pick out a vocal from the entire mix, I put on headphones. That should tell us something about the drawbacks of of additional room ambience shouldn't it ?

The only problem with this approach is the voice seems to be coming from within my head rather than in front of m :D.

Brent

Kal Rubinson

10-28-06, 07:49 PM

Texas Aggie

11-01-06, 12:02 PM

I am currently in the design/build stage of a new house. I have read most of these posts(whew!) and will be using the green glue. My room is 28'4' D 18.4' W and 10' H at the screen then 9' for middle tier then 8' for rear tier/entrance.

This will be an upstairs HT over the garage. It will also have a 5.5' deep by 18' W entrance/equipment rm at the rear of the HT. (see pic).

My biggest concern is that my two kids rooms will be upstairs with this room.
Two things that make me feel better are the TWO sealed solid core doors that isolate(hopefully) the hallway and rest of upstairs, AND the staggered stud GG combo.

I worry about transmission through the floor and ceiling plates which I would assume will be connected to the rest of the house. Can I have my builder simply not connect these or is that simply not structually sound?

I think I am close on this but want to run by the experts for some thoughts.

THANKS!!!

Stima

11-01-06, 03:01 PM

As always, I preface every reply in this thread with "I AM NOT AN EXPERT!" ;)

That said, you should research "floating floors" and "floating walls" for examples of each. I can't remember the write up I found a few years back that described how to build said items (the book was for building a recording studio in a home...but the same techniques would apply), but I am certain someone here knows of some good reading material.

In a nutshell, for the highest degree of isolation you need to build a second complete room within a room. First, build a new floor that is isolated from the existing floor via elastic material. After you have a new floor you continue with floating walls and then a floating ceiling. Given you have a 10' room height, even though you definitely lose head room with this approach, I still think its a feasible approach.

I would say, if you can't build a floating floor, the MINUMUM you would want to do is get one of those pads you can set your sub on which decouples it from the floor. If you have large woofers in your fronts, you might want to consider getting pads for them as well. Again, I don't know the exact name of what I am referencing, but I know they are out there and are used with good results.

Hope this helps.

star_gazer

11-02-06, 10:08 PM

eugovector

11-02-06, 10:41 PM

I have noticed a few other posters express concerns about (nearly exposed) fiberglass in reach of small children. I share this concern, but don't know what the alternatives are. Any suggestions? A small price and or performance penalty is acceptable.

Thanks for any input.

You just need some thin polyfill and loose cotton fabric. See the pictures and walkthrough in my thread: http://www.avsforum.com/avs-vb/showthread.php?t=734181

Stima

11-03-06, 01:15 AM

Honestly, GOM is VERY thick. You can not see or feel the fiberglass through it. I would honestly have no concerns with only using GOM.

Terry Montlick

11-03-06, 08:32 AM

If you want something equivalent in performance to semirigid fiberglass, use acoustic cotton in either 3 pcf or 6 pcf density. This is available from Acoustical Surfaces Inc. under the name " Echo Eliminator":

http://www.acousticalsurfaces.com/echo_eliminator/echo_photos.htm

Regards,
Terry

KERMIE

11-03-06, 01:53 PM

Guys I know this in not ideal but it is what I have to work with..cosmetics is a part of it (WAF)

Here is a sketch of my room.

i have a wall that comes into play that goes about 2/3 rds of the way, then an opening, then a small wall (2 foot)

The hallway is about 3 feet wide that goes upstairs.

I have base traps floor to ceiling in black in these corners. I know the small wall corner may not do much but it was the WAF again.

What can I do where the yellow Star is and will it make a difference.

http://home.mchsi.com/~fun_pictures/Layout.JPG

KERMIE

11-03-06, 01:57 PM

This is not to great scale, the rears are close than they look....

where is says "Wall" that is open

thanks for the help

TumaraBaap

11-05-06, 04:56 PM

Actually, the latest research by Toole, Olive, et. al. strongly suggests that diffusion is very much under used and absorption is very much over utilized.

That's the conclusion I too would draw reading most of the posts here. However, I think Toole's take home point was that reflections, absorption and diffusion when used should not be frequency specific lest it unbalance the off-axis endeavor of the loudspeaker. Absorption and diffusion aren't discussed in great depth. As pointed out on post #1660 and #1671 of this thread, the oomph of his review paper was in the discussion of reflections. Given how entrenched some acoustics ideas are here, I'd anticipate a fair amount of resistance to his enthusiasm for lateral reflections.

Tumara Baap

pepar

11-05-06, 07:01 PM

Given how entrenched some acoustics ideas are here, I'd anticipate a fair amount of resistance to his enthusiasm for lateral reflections.
My observation in my theater is that eliminating the first reflections coming from the left and right front side walls increased clarity, improved imaging, widened the front sound stage and improved mains/surround integration. Any thoughts on why when that doesn't square with Toole's position?

TumaraBaap

11-05-06, 10:06 PM

My observation in my theater is that eliminating the first reflections coming from the left and right front side walls increased clarity, improved imaging, widened the front sound stage and improved mains/surround integration. Any thoughts on why when that doesn't square with Toole's position?

This is indeed the opposite of what Toole claims in his paper, with the exception of imaging, which he claims can change size and position. And when it does happen it is not necessarily bad. The width of the soundstage should actually widen with reflections. One reason I hazard to put forth for your observations is that very few loudspeakers will yield a spectrally similar reflection to its on-axis response. The NHT Xd or Linkwitz's Orion just may be one of a kind. Aczel's review of the Orion (which was way before the Toole paper) corroborates just about everything Toole claims in his paper.

In line with conventional wisdom my room currently has side wall absorption. I haven't had time yet to conduct comparisons with and without the absorption. I have a set of B&W CDM1Se's. Like the vast majority of "iconic" brands of loudspeakers on the consumer market, they're hardly up to par. I won't even be bothering with them. It's my Mackie HR624 that I'll run through the paces.

One thing that impressed upon me from the paper is how any acoustic implementation ought to be weighed on its degree of reduction of interaural cross correlation. If what impinges at a given moment in the right ear is different from the left ear, it gives the organ in between a wealth of cues in determining the richness of the sound field. That comb filtering in a room can under certain circumstances be a pleasant thing is not the only surprise in the paper.

Toole is unwaveringly scientific in his approach. Speculation or hard evidence is accordingly delineated. His methods for experiment or literature review rigorously account for bias and confounding effects. What he proclaims should never be taken lightly, my man!

Tumara Baap