Question about inside out wall

I'm not sure if I have this correct. If I want to build an inside out wall in the control room, is this the right order of materials? (Going from live room to control room) Double drywall / roxul / air / double drywall / roxul / fabric Also, how much will this effect isolation?

drywall/insulation/air/insulation/drywall will give you more isolation than the drywall/insulation/air/drywall/insulation/cloth (this second being an inside-out wall) but the second one can help conserve space by building the absorption into the wall. if you can increase the air gap in the second and increase the insulation (which could be R11-R19 batts instead of mineral wool) you could achieve roughly comparable results. Eric Desart has some terrific MSM calculator spreasheets that can help get you into the ball park. I'm not sure there are detailed empirical measurements done on inside-out partitions.

I'm still in the construction phase, but the framing and drywall for the drum iso room is finished. 2 of the 4 walls are inside out walls. The building is a detached garage built in 1913. Listening test results from the outside so far: voice- inaudible boom box on max- inaudible (and it's ear shredding inside the room) hand percussion- inaudible rack toms with sticks- inaudible electric guitar with sub octave pedal at spinal tap volume- ultra low end audible 10-15 feet away. The low end might be due to the fact that I was forced into building a 3 leaf system due to the odd original construction of the building. My wall sandwich from outside in goes like this: -fiberboard siding/tar paper (weak leaf 1) -steel studs -2 layer 5/8" drywall (leaf 2) -4-5" air/insulation -wood frame inside out wall -2 layer 5/8" drywall with green glue (leaf 3) With all of the inaudible stuff, you have to literally put your ear on the siding to "feel" the vibrations to know something is even going on inside. Needless to say I'm really pleased with the performance.

Wow. Thanks so much guys! Should I be using the Roxul AFB on the live room side and the R11 in the control room still? I'm assuming that the R11 will have no effect on the Roxul because there will be drywall between the two.

You can just use the cheap pink fluffy fiberglass between the walls and get the same performance...I've actually read that it may even be slightly better in the low end. As you can see from the pic, I don't have any actual "open air" space between my 2 heavy leaves. The original walls were not plum, so I used 6" fiberglass and doubled it up as needed to slightly compress it to dampen the drywall on both leaves. It worked great, just be sure to NOT pack it in so tight as to couple the 2 leaves together. I still have not acoustically tuned the room, so I don't have any fiberglass/roxul/etc at all in the internal inside out wall cavities yet.

Awesome. Thanks so much for the input! You guys are the best. I was also wondering what I should be using at the joints of the drywall. I'm already planning to use Green Glue between the drywall layers. Should be using the GreenSeries Caulk http://acousticalsolutions.com/products/sealants/green_series.asp where the pieces of drywall join together? I'm reading Rod's book, but I can't remember if I read anything about that yet.[/url]

That stuff is expensive! Where the sheets of drywall meet, just mud and tape your joints as you would a regular bedroom wall. Around the edges (like where it meets the floor etc.) leave a 1/4" gap and stuff closed cell foam backer rod in that gap and then seal it with acoustic caulk. I used USG acoustic caulk. It's easy to work with, doesn't stink up the place, and is not priced for Bill Gates. Green Glue is expensive too, but it's worth it. The cool thing about that stuff is that you can do partial coverage and get most of the potential performance...which is what I did.