"You're simply saying to cut the drywall to approx 22" to fit between the studs and against the lap siding? "
Yeah, that's exactly what I'm saying - you want more mass in the outer leaf of the wall (where the stucco is), then you want as much air space (with insulation, it's still acting as air space but with better Transmission Loss)
"Would it be a waste to put up new construction paper as well." -
No, in fact it would be a good idea. you will need a good vapor barrier , and since the sheet rock needs to be kept dry, I would put Tyvek house wrap between the studs before adding the two layers of sheet rock up against the outer lap siding. You could then put standard fiberglas insulation between what's left of the studs, move in at least 4 inches, and put up a steel stud wall with RC on the studs horizontally, then at least two layers of sheet rock on the RC. Do NOT put any paneling whatsoever on the INSIDE of the steel stud frame. Remember, only TWO centers of mass (leaves) and only ONE air space.
If possible, don't break either wall surface for electrical - running surface mount boxes and wire mold will keep the TL of the wall better.
When building ALL of this, think like you're in a submarine and don't want to drown. The least little (and I mean REALLY little) crack will screw up most of your soundproofing attempts, so caulk EVERYTHING. The ideal wall is two layers of mass, totally isolated from each other, and totally un-broken. The closer you get to this, the better the TL.
If you can't find the REAL acoustic-rated caulk locally, post back - I have links to online purchase of both the 1 quart tubes of caulk, and the contractor caulk gun you need to put it down. Do NOT, repeat NOT, use butyl or silicone caulk that isn't acoustic rated. That stuff costs $3-$5 a tube for 10 oz, and the acoustic stuff, even online, is only $7.50 a tube for 29 oz - that works out to about $2.50 a tube if you were using the 10 oz. I just talked to a guy in San Diego yesterday, and his local Home Depot had RC (mine doesn't) he also was able to find a commercial insulation place that carried the acoustic caulk in 29 oz tubes for $3 a tube.
Remember, the absolute best use of materials you can get is to use ALL the mass in only TWO leaves, inner and outer, with only ONE air space. The more mass in the leaves, the better the Transmission Loss (TL for short) - The wider the AIR gap, the better the TL. Using 3 lb/cu ft density mineral wool in the air gap gives the best overall TL; higher density improves bass blocking some, but at the expense of high freq blocking. Lower density insulation helps highs some, but worsens low freq response. With live drums, you'll want 3 PCF or a little higher. You'll probably have to hit a commercial insulation place for this kind of stuff.
As to space, I doubt if your room is quite big enough for two rooms - I'd see if John can figure anything, he's a wizard at coming up with designs like that... Steve
