Acoustical Treatments Master Thread - Page 290

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

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

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

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

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

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

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

welcome to acoustics.

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

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

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

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

Cool it with the personal comments guys...

And I guess the owner of this magnificent theater:

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

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

Cheers

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

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

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

Question about acoustically transparent fabric:

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

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

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

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

Opinions?

Thanks.

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

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


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

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

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

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

Cheers,

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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

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

Someone needs to write the Room Model Primer

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

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

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

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

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

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

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

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

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

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

Do so in a way that can be...

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Yamaha made that rather reasonable approach starting with the DSP-1

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

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

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

Jeff

+1 and leave this one for theory banter.

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

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

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