# Treatment for side walls / reflection points



## ALMFamily (Oct 19, 2011)

I am trying to determine how wide my trim needs to be on the side walls - is there a standard / suggested thickness for 703 on side walls to treat reflection points?

If so, does it adhere right to the wall or should a gap be left between the wall and the 703?

Thanks!

Joe


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## Prof. (Oct 20, 2006)

Joe..I found that 2" Ultratel (OC705 equivalent) panels spaced 2" off the wall worked best for me..


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## ALMFamily (Oct 19, 2011)

Prof,

After looking at a couple other builds, it looks like others have just been affixing the 703 right to the wall and not leaving a gap between the 703 and the wall. I am assuming they are not leaving the gap due to space constraints.

I read Simon's process and saw you suggested just to put the cloth right over the 703 and staple it to furring strips and not build boxes - this is what I was thinking I would do. However, if I use 2" 703 and then leave a 2" gap, I would have to use a 4x4 to get the trim to mount flush with the insulation / cloth. That seems a bit excessive. If I understand correctly, leaving the 2" gap allows for the sound waves to in essence go through the 703 twice - once on the initial path and then the resulting reflection of the wall. Is that correct?

It seems I am missing something here that would make this much easier...........


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## robbo266317 (Sep 22, 2008)

Yes, It's the same with corner chunks. You get more benefit by having the wave traverse the material twice


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## Prof. (Oct 20, 2006)

ALMFamily said:


> Prof,
> 
> After looking at a couple other builds, it looks like others have just been affixing the 703 right to the wall and not leaving a gap between the 703 and the wall. I am assuming they are not leaving the gap due to space constraints.
> 
> ...


Simon's acoustic treatment was not your conventional panels fixed to the wall type..He covered his entire walls with 2" insulation (Ultratel) and then covered that with GOM..
If you're planning that type of treatment, then the insulation just fits against the wall..No need for any gap..


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## Prof. (Oct 20, 2006)

Joe..I should add that it's not necessary to cover your walls with insulation, unless you have a large room..

If you're doing this on the basis that you prefer not to see any panels on the wall..then you can do a partial covering of the walls..


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## ALMFamily (Oct 19, 2011)

robbo266317 said:


> Yes, It's the same with corner chunks. You get more benefit by having the wave traverse the material twice


Thanks for the confirmation Bill!



Prof. said:


> Simon's acoustic treatment was not your conventional panels fixed to the wall type..He covered his entire walls with 2" insulation (Ultratel) and then covered that with GOM..
> If you're planning that type of treatment, then the insulation just fits against the wall..No need for any gap..





Prof. said:


> Joe..I should add that it's not necessary to cover your walls with insulation, unless you have a large room..
> 
> *If you're doing this on the basis that you prefer not to see any panels on the wall..then you can do a partial covering of the walls..*


Thanks Prof - this is what I had planned. I was going to do partial covering of the walls with insulation inside of furring strips. Then, I was planning to cover all the walls with GOM to hide the insulation. I would also be covering untreated areas of the wall, but I thought it would look better to maintain consistency. I would staple the GOM to the furring strips and then cover the furring strips with the finish trim.

Does that make sense at all or am I just rambling again? :R


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## Prof. (Oct 20, 2006)

That sounds fine Joe..


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## ALMFamily (Oct 19, 2011)

Thanks for the help!


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## Bullitt5094 (Mar 5, 2012)

robbo266317 said:


> Yes, It's the same with corner chunks. You get more benefit by having the wave traverse the material twice


Just learning so I'm curious, doesn't the sound go through the material twice even without a gap behind it?


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## Prof. (Oct 20, 2006)

It does go through the material twice, but i believe having a gap provides a bit of additional decay and dispersion of the reflected sound..


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## ALMFamily (Oct 19, 2011)

Thanks Prof - that is what I was thinking but was not 100% sure. Cheers! :T


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## HopefulFred (Jan 20, 2011)

Leaving the gap also puts the insulation in a position to have greater influence on lower frequency sound than it would closer to the wall - broadening the effectiveness. Porous absorption, like OC703, works by slowing down high-velocity air molecules as they transmit the sound wave. In general, the air at the walls moves the least; especially for low frequency sound, where the wavelength is much larger, the extra distance is beneficial. I read that generally 10% of the wavelength is a good thickness. So for lower frequency sound - say 400Hz - the wavelength approaches one full meter (around 0.85m for 400Hz), so 3.5 to 4 inches is "rule of thumb" appropriate. The functional difference between two inches of absorber two inches from the wall, and four inches of continuous absorber is very small. (There are lots of assumptions and generalities in this figuring, but that's the situation in a nutshell)

Fred


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## Bullitt5094 (Mar 5, 2012)

Prof. said:


> It does go through the material twice, but i believe having a gap provides a bit of additional decay and dispersion of the reflected sound..


Continuing to learn... I have 4" 703 I was about to carve into triangles and fill the corners of my room. Would it be better to leave them as panels and span the corner of the room instead. That would leave the area in the corner behind them open. Any advantage to that?


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## Prof. (Oct 20, 2006)

Super chunks in the corners will be far more effective than using 4" panels across the corners..
To get the equivalent of corner chunks, you would need 6" thick and 24" wide panels across the corners..


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## Bullitt5094 (Mar 5, 2012)

So space behind the wall panels that are mainly treating higher frequency reflections, benefits from having some open air behind it. But on the lower frequency treatments in the corners, it's better to have full density all the way to the walls? Again, just trying to learn stuff. I would have thought just the opposite. That is wouldn't matter much on the wall reflections because it's collecting small wave forms, but it would help to have space on the corners. That in the corners the additional transition from one density to another would change the speed of the wave two more times and thus disperse the larger wave length more by breaking it up. Maybe even reflect and trap some energy back into the corner from the back-side of the panel. Again, not anything close to an audio engineer and I'm not questioning your statements AT ALL, but I'm very curious and want to learn. :T


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## ALMFamily (Oct 19, 2011)

I am just guessing here, but could it have something to do with the fact that drywall will reflect higher frequencies while lower frequencies will not reflect as much? 

I thought that some of the energy from the lower frequencies would pass through the drywall which is why decoupling the walls from the studs is so important.


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## Prof. (Oct 20, 2006)

Joe is right..Low frequencies will pass through just about anything..including brick walls, so they need to be absorbed as much as possible..
The low to mid frequencies can also produce standing waves in your normal room environment, resulting in peaks and dips in the frequency response..The corner bass traps and wall panels combined help to smooth the overall response..


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