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Acoustical Panels... what should I use?

573 Views 2 Replies 3 Participants Last post by  Ethan Winer
I posted this under Acoustical Treatments Master Thread, however, it seems like everyone on there is into bass traps right now...

Here was my original post:


I don't understand which type of acoustical backing I should use on my back and side walls. What is the rule of thumb? Over 40 pages of posts, and I still don't understand what you all are talking about.


I was thinking of using homosote? Would that do the trick?
Here is a response from Dennis:

Whether or not you want diffusion or absorption in the areas indicated will depend on several factors:

1. Are these panels in mirror points for the seating positions? If so, if your speakers have excellent off axis response, you want diffusion. With poor off axis response you'll want absorption.

2. Based upon the total of all materials in the room, what is the predicted decay time and, based on that, is more, or less, absorption needed (at what frequency ranges)

3. And, be real careful about bass traps. Most of them do nothing in the 80Hz and below range ... the first three or four (and most audible) axial modes in the typical room are below 80Hz. Most bass traps are also serious absorbers at all frequencies above 120Hz and can result in over absorption, reduction of room reverberation way below what you'd want, and you can find yourself needing to get more powerful amps and then speakers that can handle the addition power.


D. Erskine

Design Cinema Privee

Architectural Acoustics

Design/Build - Worldwide

GA - TX - MN
Here is my question that was never answered due to bass traps:

Thanks Dennis & bpape for the response.

Dennis, I do have a couple questions...

1) you state that if the panels are in mirror points (first order reflection point), I'll want diffusion. What material is recommended for diffusion? Then for the reset of the panels, what is recommended? Plywood? Homosote? Fiberglass?

2) How do I figure out the predicted decay time? The room is 20x15 but the actual area (non-stage) is about 16x15. The stage and room is carpeted, I do have wood panels on the angled part of the stage left and right (see rendering above).

3) Bass traps... I'm clueless... wasn't even considering them.

Thanks for the help... I'm doing fabric stretch walls, so if I don't get it all right the first time... the idea is, I can tweak them later...
Thanks for the help folks!

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There are plenty of us that will design room treatments for you - but Dennis is the best it gets as far as advice. Dennis is referring to unpublished Harman International research regarding absorption/diffusion at mirror points depending on off-axis response. Generally members of AES/ASA are up to date on the latest research. If you find an acoustical engineer too expensive for your tastes - then check out homeacoustics.net for a list of experienced HT installers with acoustical training offering design and calibration services.

You can find out the basics of predicting reverb if you buy the Master Handbook of Acoustics by Everest - the best book on acoustics there is written for the average joe with very little math. You need to be able to write a simple spreadsheet for the basic model - but reverb calculations can get very complex with advanced models. If you plan on designing it yourself - at least buy the book - otherwise you will be held hostage by treatment sellers whose treatment plans just happen to be what they sell. Nobody can really say which panel goes here unless they have come up with an entire treatment plan for the room - which is likely why your specific question has gone unanswered.

Basically with a spreadsheet you can figure out the absorption of your room without treatment - then what absorption do you need to add at what frequencies. Then you search out the panels and figure how much are needed to get that absorption, but this also assumes you know what the desired reverb of the room should be.

BasementBob has an excellent website with a database of absorbers. But you also need to factor in what brands are available to you at what price- as warehouses do not carry everything.
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