More Insulation vs. More Airspace

Audio Elements · Post by **Audio Elements** » Fri Aug 20, 2004 9:39 am

Ok guys, so I have a couple spaces where the space between the double walls gets fairly large:
one of them is 18" apart at the widest (7" at narrowest), and another is 3' at the widest.
(See the space between the control room and the shop,
and to the back right corner of control room in the pic below.)
This is measured from frame to frame, not sheetrock to sheetrock.
I've read that the airspace is important and effective, as well is insulation.
These walls are double walls with
5/8"-5/8"-frame-rockwool-airspace-rockwool-frame-1/2"-1/2"

So what would be most effective?
Leave the space dead air, or stuff it full of insulation?
Any suggestions?

NOTE: grey rectangle to right in pic is a (now) interior stone
retaining wall that comes up about chest high, with framing
to outside resting on that.

knightfly · Post by **knightfly** » Sat Aug 21, 2004 1:05 am

You'd get better isolation filling with unfaced fiberglass, but maybe not worth the cost/effort - with that wide a gap, you might see another 2-3 dB isolation by filling with insulation instead of just the stud frames . If you can afford it, I would go ahead and fill the cavity but don't use 3 PCF rigid for the entire cavity, only against the wallboard. The normal, fluffy fiberglass in UN-faced is as good or better for studio use once you have the rigid stuff against the wall panels... Steve

z60611 · Post by **z60611** » Sat Aug 21, 2004 9:27 am

Knightfly

In this thread you wrote

If you can afford it, I would go ahead and fill the cavity but don't use 3 PCF rigid for the entire cavity, only against the wallboard. The normal, fluffy fiberglass in UN-faced is as good or better for studio use once you have the rigid stuff against the wall panels

But in this thread you wrote

it's better to use 703 or SAFB's on BOTH sides of a wall, partly for damping

Just so I'm clear, you're suggesting double stud walls be built as follows:
a) gypsum
b) woodstuds and 3pcf insulation
c) airgap with fluffy insulation
d) woodstuds and 3pcf insulation
e) gypsum

knightfly · Post by **knightfly** » Sat Aug 21, 2004 10:03 am

Right - couldn't have put it more succinctly...

Just so you know to be at least slightly wary - this is a "gut feel" thing on my part, based on USG's recommendation for 2.5 PCF being best for music walls, their comments about lighter insulation being better for bass TL, the cost of a foot or two of ALL 703, the thought that VARYING insulation density in a wall seems like it should "confuse" the sound more

, the knowledge that a light pressure against centers of wall panels reduces ringing, and the IRC wall document (linked here by Andre I think, sorry I don't have time to look - it's IRC-761, or something like that) , and probably a few dozen OTHER things my brain has absorbed in the last 20 years or so -

Bottom line is, YMMV - but this is, at this point in time, the way I intend to build most of the walls in my next facility... Steve

AVare · Post by **AVare** » Sat Aug 21, 2004 10:34 am

Here is the link to IR-761

http://irc.nrc-cnrc.gc.ca/fulltext/ir761/

You may find this useful also. It is like "IR-761 in useable guidelines"

http://www.cmhc.ca/publications/en/rh-p ... -108-e.pdf

Enjoy!
Andre