STC rating of this wall?

[OzNimbus]

Hello all, here's a simple question I haven't been able to find the answer to.

I've been going over John's designs, specifically, his "Project studio wall."
You know the one on page 1 in the recording manual.... The 2 by 4 wall with the slot resonator built in, sealed up with drywall on the outside, and an extra layer of insulation on the outside.
This one: http://www.saecollege.de/reference_m...ages/Walls.htm
Unfortunatley, I haven't been able to find an STC rating for this wall ANYWHERE. I'm thinking on using these walls in my drum room (My outside walls are 8 inch concrete) but I'd like to know how much these walls will isolate.

Also, for the sake of argument, if you had 2 walls BOTH with an STC of 45 separated by a 2 inch air gap, what kind of STC rating would you get for the both of them combined? Is it just simple addition (like 90) or does it work by a formula?

Thanks,
-0z-

[John Sayers]

I'm sorry I can't give you a STC rating for the wall but at Left Bank, where the outer wall is timber you can just hear the kick drum low end

cheers
JOhn

[Transputer]

Oz, over on http://groups.yahoo.com/group/acoustics/files/
is MASS-SPRING RESONANCE xls file. You may have to join the group to access the file, lots of good info over there BTW.

Cheers

[laptoppop]

Originally posted by OzNimbus
Also, for the sake of argument, if you had 2 walls BOTH with an STC of 45 separated by a 2 inch air gap, what kind of STC rating would you get for the both of them combined? Is it just simple addition (like 90) or does it work by a formula?

I believe that is is not that simple, darn it! The air trapped between the walls can make the walls act as a drum. It can couple the sound especially at certain frequencies, so you can't just add the STC ratings. I've seen some recommendations for filling the space with insulation to cut down the air coupling -- but I would think that if you put too much in, you'd get physical coupling from the insulation! Bottom line is that I'd expect you to get some nice improvement with a second wall, but not 90.

Oh well. I give up. I think I'll just put up some 4 feet thick concrete walls on all sides. Trust in mass!! Nothing will get through that!! Oh wait, how about doors and air? ::::sigh::::

-lee-