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We're having a contractor put up drywall with fiberglass insulation behind it to cover the cinderblock walls in our basement (soon to be an audiophile listening/spare HT room).

I was wondering if instead of putting acoustic treatments over the drywall if we could replace the drywall with the treatments themselves. Does anyone know where we could get materials to accomplish this?

Here's a link to an 'ideal' HT room we were hoping to approach. Btw the basement is basically a square box.
Thanks for any info!
 

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Quote:
Originally Posted by Acropora /forum/post/15427772


We're having a contractor put up drywall with fiberglass insulation behind it to cover the cinderblock walls in our basement (soon to be an audiophile listening/spare HT room).

I was wondering if instead of putting acoustic treatments over the drywall if we could replace the drywall with the treatments themselves. Does anyone know where we could get materials to accomplish this?

Here's a link to an 'ideal' HT room we were hoping to approach. Btw the basement is basically a square box.
Thanks for any info!

Since you hired a contractor, I assume he got the proper permits, and that you will have to have this inspected by local officials. Usually, any insulation is required to be covered by drywall, or another fire retarding material.
 

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Quote:
Originally Posted by Acropora /forum/post/15427772


We're having a contractor put up drywall with fiberglass insulation behind it to cover the cinderblock walls in our basement (soon to be an audiophile listening/spare HT room).

I was wondering if instead of putting acoustic treatments over the drywall if we could replace the drywall with the treatments themselves.

In general acoustic treatments of an absorbtive nature are designed to augment an existing room of a fairly conventional nature.


A good sounding room has a mix of reflection, absorbtion, and diffusion. Only diffusion elements are able to replace the function of a traditional wall. Absorbtion elements typically presume that there is a standard reflective wall behind them. Indeed, many absorbtion elements depend on reflections off the wall for some of their effectiveness.


One rule of thumb is not to have your acoustic elements be large and unbroken areas, but rather to have smaller areas of each kind of acoustics element that are intermixed.


Here are some links to articles about the basics of room acoustics:

http://www.realtraps.com/

http://www.stereophile.com/roomtreatments/

http://www.audioholics.com/education...cs-principles/
 

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Quote:
Originally Posted by Acropora /forum/post/15427772


We're having a contractor put up drywall with fiberglass insulation behind it to cover the cinderblock walls in our basement (soon to be an audiophile listening/spare HT room).

I was wondering if instead of putting acoustic treatments over the drywall if we could replace the drywall with the treatments themselves. Does anyone know where we could get materials to accomplish this?

Here's a link to an 'ideal' HT room we were hoping to approach. Btw the basement is basically a square box.
Thanks for any info!

no no no! what you want to create is a damped wall, essentially one that is flimsily mounted and so vibrates in order to absorb instead of reflect very low frequency sound. since you haven't put the wall up yet, it's not a big deal and will solve almost all your low frequency sound problems right from the start. and, you only need to do this to one of the opposite walls (for example the left side wall, and the rear wall). this will reduce axial modes to near zero. i forget what the technique is called. good luck.
 

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Quote:
Originally Posted by LTD02 /forum/post/15457841


no no no! what you want to create is a damped wall, essentially one that is flimsily mounted and so vibrates in order to absorb instead of reflect very low frequency sound. since you haven't put the wall up yet, it's not a big deal and will solve almost all your low frequency sound problems right from the start. and, you only need to do this to one of the opposite walls (for example the left side wall, and the rear wall). this will reduce axial modes to near zero. i forget what the technique is called. good luck.

I only wish there was such a technique! About the only thing I know of which can "reduce axial modes to near zero" (which I'll assume to be a max of 10% reflection) is to build a custom membrane/porous bass absorber for the entire wall. This will take a few feet of wall thickness. If your room is 20 feet long, then my back-of-the-envelope calculation says that 6 feet of bass absorber depth is required to kill all the axial modes down through the first, at 28 Hz.



Regards,

Terry
 

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Quote:
i forget what the technique is called.

It's called "bad" technique.



Attempting to use a wall as a diaphragmatic absorber (particularily a broadband device) creates more problems than it solves (if it even solves the problem you're attempting to fix) and, frankly, needs to be placed into the same bucket as green magic markers on CD's and purple silk on speaker cables.
 

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The number one thing one can do to help in the bass region, is to start with proper room dimensions (Terry has a great Excel room size calculator on his website). As far as what to do once you got the room dimensions down, I will leave that up to the local experts such as Terry and Dennis.
 

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Quote:
Originally Posted by LTD02 /forum/post/15457841


no no no! what you want to create is a damped wall, essentially one that is flimsily mounted and so vibrates in order to absorb instead of reflect very low frequency sound. since you haven't put the wall up yet, it's not a big deal and will solve almost all your low frequency sound problems right from the start. and, you only need to do this to one of the opposite walls (for example the left side wall, and the rear wall). this will reduce axial modes to near zero. i forget what the technique is called. good luck.

I believe but am not sure, that this is a technique that Earl Geddes uses. Earl occasionally posts here so perhaps he can respond and either confirm that this is not his approach or defend it's useage.


His chapter from a book (that was written several years ago) on room acoustics is here-

http://www.gedlee.com/downloads/Chapter%204.pdf


Since I know Earl is going to Alma and then CES, it may be awhile before he responds.
 

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This business of using flexible walls to reduce modal reponse (or other bass response issues) in rooms is wrong on so many levels. Let's look at a few of them:


1. Standard framing is 16" O.C. As such every wall cavity will resonate at the same frequency and Q (in a perfect world). Bass problems encompass a significant number of frequencies, not just one. (typically, standard framing will provide for either a 3.5" or 5.5" cavity depth...again, consistent throughout the space). You are just as likely to absorb (over absorb) a frequency which needs to be boosted as you are to absorb a frequency which needs to be reduced (and hopefully the Q of the wall will match the Q of the problem...if it does, buy a lottery ticket for me).

2. The usual matra is to use a single layer of 1/2" drywall. Examining the characteristics of 1/2" drywall will quickly tell you the effect of the diaphragmatic absorber will vary based upon whether the drywall is applied vertically vs horizontally.

3. Framing may be wood studs or steel. You'll have a difference between these two due to their different flex properties. You'll also have differences based upon code compliance...such as fire blocks, shear walls, etc.

4. In every case where someone has purported this worked well and I subsequently measured the room, it hasn't worked at all...at least not as described. The fact is the room exhibited the modal characteristics of the room itself AND, at some frequencies, the modal chacteristics of the room+surrounding rooms. IOW, the bass was simply passing through the boundary to the next more massive wall (like a foundation wall). They achieved some differernce (not a fix) simply due to the fact the bass was responding as if it where a larger room (at the ire of the wife, children, neighbors, and pets).

5. The performance of such a wall cannot be reasonably predicted. If it cannot be predicted you (a) don't know if this type of construction will fix your problem or (b) if it will create a problem you didn't otherwise have.

6. There are far better, far more predicable, more focused methods and materials which are available to resolve bass response issues, why would anyone want to use a less reliable, less controllable (once built), less predictable method.

7. If you rely upon the use of an unpredictable structure to fix a problem, and it doesn't fix the problem (or it creates other problems), ask yourself this: "Is it more expensive to replace the wall or to move a bass trap (or buy one in the first place)?"
 

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I know that Earl does not believe a flexible wall "solves" all the modal issues and I don't think he advocates standard framing, but I don't have the book with me at work. I think his method does not create a cavity as you described. He does believe in a multiple subwoofer approach but uses a more random approach than Welti.
 

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In any case, it is important to understand what Todd's research is saying...basically, such layouts provide "consistent" response over the seating area ... not necessarily good response. However, once your seating area is consistent, your calibration efforts are also reasonably consistent. I'm rather confident Earl's placements are NOT "random". The results he obtains can be approximated by the HAA's "virtual" subwoofer methodology. At the end of the day, multiple subwoofers, when you can individually set phase and SPL provide significant advantages in tuning bass response in a room.


While Earl does not suggest flexible walls fixes all modal problems, crux of the issue is that using such construction techniques is not likely to fix any modal problem (it's more likely to move a modal problem to an unexpected frequency) and will induce other problems far more difficult to address (and, I for one, don't like my walls becoming secondary speakers). Since other more effective means exist to resolve bass response issues, I am not willing to sacrifice sound isolation in order to get unpredictable bass response.
 

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Quote:
Originally Posted by Dennis Erskine /forum/post/15464044


Of course there is a cavity! Standard construction methods leave you a cavity whether you want one or not. (That cavity may be the next room.)

Here is what he suggested in a book written quite awhile ago-I didn't think it was that different from your suggestions, but I may be wrong--


"Geddes talks extensivly about a double layer of sheetrock on the RC with a mastic material in between the 2 layers of sheetrock. He uses "Liquid Nails for sub flooring" to act as the mastic."


Do you not recommend that except with green clue?


As far as Welti's approach and Earl's I know that Earl's is not completely random. I think it is best to let him speak for himself though as I am not defending his approach. However, his theater was the best I have heard especially with regard to bass implementation. I also know that despite Welti's paper and approach when I took the HAA Level 2 course, we did not end up with the two subs in precisely the manner recommended by Welti (and it measured darn well). We tried the virtual subwoofer method of course, but ended up with better measurements by modifying it slightly-good start though. Earl talks about a minimum of three but they don't have to be very expensive.


You appear however to know more about Earl's approach than a casual understanding and so you know that he TOO is pretty sure of his approach:)
 

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Two layers of sheet rock bonded with adhesive on old fashioned RC channel won't provide any flex. The old RC cannot take the weight. Drywall (mass) with Green Glue (absorption) and clips (mechanical isolation) are a good entry level combination.


Making a hotel room sound good is a pain in any case. If you did this course in Bellevue, you also noted the modal response included not only the room boundaries but the boundary from the hall as well.
 

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Quote:
Originally Posted by Dennis Erskine /forum/post/15464412


Two layers of sheet rock bonded with adhesive on old fashioned RC channel won't provide any flex. The old RC cannot take the weight. Drywall (mass) with Green Glue (absorption) and clips (mechanical isolation) are a good entry level combination.


Making a hotel room sound good is a pain in any case. If you did this course in Bellevue, you also noted the modal response included not only the room boundaries but the boundary from the hall as well.

Yes and yes.
 

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With due respect to Dennis, I think a properly designed and executed damped flexible wall might be useful. If you can tune the walls to absorb the primary mode that gives you one less room mode to worry about. This can be done using helmholtz absorbers, or tuned/damped absorbing membranes. Since any wall you make in a basement is not load bearing you have more flexibility to space supports as needed (or use none). The problem is they are difficult to design and implement properly - they can be easily designed to work very well, but then the the materials used change their moisture content and you end up absorbing a frequency you did not intend. It can be a crap shoot - sometimes you might be better off using something that at least has known and fairly constant properties. In any case, make sure whatever you build cannot rattle! Unfortunately in this game there is no right answer, you just do the best you can. If I was designing a room from scratch I'd consider using a combination of tuned helmholtz resonators - tuned damped membranes - and broadband absorbers (lots of these) - hoping that somehow they would work well together. But since my walls are already built I just stuff as much thick high density fiberglass/rockwool as possible without overdamping mids and highs. The advantage of tuned absorbers is they take less space, the disadvantage is they are tuned (and that tuning may change with time)
 
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