Dreaded street noise vs. soundproofing

[jonothon]

I'd love some advice regarding soundproofing. I've got a normal existing exterior wall (drywall on inside, siding and brick on the other) onto which i've put a layer of 1/2" celotex and a layer of 1/2 drywall. I've built a 2x4 wall an inch inside and I'm still up in the air about exactly what to put on that. 2 layers of sheetrock and a layer of celotex? I bought a bunch of resilient channel, will it hold all these layers? Or should I put the RC on after a couple of layers of something, and then put a final layer of rock on that? On top of all that will be tongue and groove or acoustic paneling, something like that.

Give me the good news or the bad news. How am I doing? And what should I do different?

 

[jonothon]

and here's a jpg of the proposed layers. By the way, what would be the preferred sequence of layers? the diagram shows RC, drywall, celotex, drywall, but I have no idea what order makes the most sense.

 

[jonothon]

no one has opinion on this? come on, somebody here can help, i'm sure.

 

[knightfly]

Have you checked out the SAE site John has so thoughtfully set up?

http://www.saecollege.de/reference_material/index.html

Tons of info there, click on STC and Construction links and read it all. Also, go to

http://www.studiotips.com/

click on file area, and scroll down to absorption tables - shows the absorption characteristics for several different materials. for example, ceiling tile (Im' assuming similar to Celotex - is shown as
Ceiling Tile, standard
0.10 0.28 0.66 0.91 0.82 0.69 Where the numbers are absorption in Sabins at 125, 250, 500, 1k, 2k, and 4kHz. compare to drywall, which is
Drywall, 2 layer 5/8", on 2 x 4's,
0.02 0.02 0.03 0.04 0.04 0.03

My point here is that even though sound transmission is hindered more by changing medium, which suggests the rock/celotex/rock approach, that you might benefit more by the increased absorption of having the Celotex on top. Although, if you're going to panel the wall, putting the celotex in the middle probably makes the most sense due to the changing medium effect.

All this is pointless if you haven't hermetically sealed every step of the way with Butyl caulk or non-hardening silicone. Also, what about the rest of the walls? if they are Shoji panels, you're wasting your time and money on the one wall you mentioned.

Even if you've already been there (SAE), you should re-read John's comments on sound proofing. There are an awful lot of factors to consider here, and any one that's ignored can bite you in the ass... Steve