MAJOR bass cancellation probs.(bass traps?) HELP PLEASE (1 Viewer)

[Ethan Winer]

Sankar,

> my thinking is that if the inclusion of RCs now makes bass management somewhat easier later, then it may be worth giving it a shot. <

Yes, it can only help - even if just a little - and the more surfaces you treat that way the better.

--Ethan

 

[Rutgar]

Sanker, sorry I haven't posted in a few days (I just got back from Vegas).

This is important. Besides RC, you also need to put two layers of sheetrock on top of the RC, with a mastic layer in between the two pieces. This sheetrock configuration creates whats called "Constrained Layer Damping", and adds a "one-two" punch to the RC. Again, buy the aforementioned book before you do ANYTHING. It explains all of the details. If done like the book says, then you won't need additional bass treatments inside the room (which take up valuble space).

- Rutgar

 

[John Prator]

Sanker,
I think you need to do a little more research. Some of the things I'm hearing here don't sound right. Have never heard you need to put two layers of sheetrock on RC, among other things. Have you gone to AVS and done some research? I would also recommend you give Ethan a call or at least email him. I'm not trying to slam anyone, just think you really should check into this more and not just go changing all your plans off of one persons advice.
John

 

[Rutgar]

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. However, he says you can also use silicon, or latex caulking. There also are some commercial products available. Here is a link to a site that sells such a product, and also talks about the double layer of sheetrock with a mastic center.

http://www.asc-soundproof.com/iso-diagrams.htm

- Rutgar

 

[Sankar]

Hi again!

I contacted Earl Geddes and since he was reluctant to comment on my questions, I decided to pay for the extra handling charges and get the book sent to me by overnight delivery.

I have read the book (its quite easy reading). It deals mainly with acoustic issues relating to small rooms (such as HTs) which it argues are somewhat different from those in large rooms such as commercial theaters.

With regards to construction, the idea is to try and dampen the low frequencies by translating the energy to motion. This is where the RC comes in ... essentially the wall acts as though mounted on springs. Furthermore, since the wall is going to be flexing, anything we do to increase energy absorption by exploting this can also benefit. To this effect he considers Constrained Layer Damping --- the principle that is also used in dampening sound using flexible mastic between metal panels in automobiles. In essence, consider the inclusion of a flexible glue (it must be non-hardening for it to work) between 2 layers of relatively stiff panels. As one side flexes, the energy is transmitted through the glue to the other side. The flexible bond between the two layers acts like a "spring" again, dissipating energy. This is indeed similar (as Rutgar pointed out) to the principles used by ASC in their Wall Damp product. What Geddes suggests is the use of a non-hardening glue such as Liquid Nails for Subfloors or latex caulk as the flexible bond between 2 layers of the walls. This is likely to be somewhat cheaper than the Wall Damp solution (which of course is more convenient).

Most writeups on dual walls atop RCs deal with sound attenuation as such. The general consensus appears that the inclusion of a second layer of RCs provides no appreciable benefits as regards sound isolation. However, in our case the objective is different. Its not sound isolation but absorption. The flexible glue will provide a "semi-stiff" bond between the two layers that could act as a means of additionally dampening the energy of low frequency waves (where the wavelength is of significant size). The dampening effect declines at higher frequencies which will need treatment inside the room as usual.

This approach will probably not solve all the bass frequency trapping problems, but it does not sound outlandish to me.

Comments, thoughts?