Wall/Ceiling construction questions

[tomk358]

First off, this site is amazing, kudos to those who regularly hand out information to the rest of us idiots.

So I've read the stickies, read the Canadian drywall reports, and also the SAE listing of STC ratings for wall construction.

I'm building a small practice space/demo-recording area for my band, in my basement. It's a typically patheticaly short (7') ceiling, unfinished basement, roughly 11'x19' floor dimensions.

There are a few things I've run into that seem to be contradictory.

First off, I've read that the weakest link in your sound isoation makes it not worthwhile to build a solid double wall when you'll have sound leaking through a shared floor slab, ceiling and through the door(s). Then I also read that the more mass you put up, the more sound you can isolate.. so which is it? I tend to think that the more there is up, the more sound will have to fight it's way to the other side of the wall... but please correct me if I'm wrong.

For the internal walls (between the studio space, and the rest of the basement) I'm planning on a double wall of 2x4 studs on 24" centers, 1" air gap, w/ R19 unfaced pink insulation, and 2 layers of 5/8" drywall on both sides. This seems like the best sound isolation wall from the Canadian research. (STC ~67?)

On this forum I've read the following:
1) heavier leaves block sound well
2) un-equal weights block sound better.
3) RC should only be used on one leaf, and is not needed when using lightweight steel studs.
4) Steel studs in sound walls can lead to moisture problems as they don't retain water like wood, so there is less wiggle room when moisture needs to be trapped before it can be dried out.

So I was considering steel studs to get the extra TL from them flexing, but then the moisture thing steered me towards wood w/ RC, but then I read that RC lessens your low end TL, and thats what we're really fighting against right? Then what about un-equal masses on the leaves? should I do one with 1/2" layers instead so they aren't the same mass on each side?

Now for the walls that are facing the outside of the building (concrete foundation) I was going to do wood studs on 24" centers w/ 2 layers 5/8" drywall, 1" air gap, R-19 unfaced insulation, and some vapor barrier- don't know where yet- still researching. I live in Portland Oregon, where it rains all winter, and is warm in the summers. Sound logical?

For the ceiling I'm doing 2 layers of 5/8" drywall up in the joists, stuffing with R19 unfaced insulation then putting in 1/2" RC, and 2 layers 5/8" drywall on the bottom. The problem is I'll have 2 steel I-beams that the ceiling joists sit on- How to sheild these from sound with the least amount of headroom loss? I was going to do a drywall/wood wrap around them, obviously it won't be as good as the rest of the ceiling, but some is better than none, yes?

Finally, when I'm putting in all these layers of drywall- do I mud and tape them as I go? then acoustic caulk the outer edges? Or could I just acoustic caulk each layer, and just mud and tape the last one? (mudding is my least favorite construction task)



Those are my questions now. Any suggestions would be greatly appreciated..

-Tom