Double width studs for isolation?

Nsgarch...I too went to MIT, but was more interested in women than calculus. Tech Hi Fi in the warehouse also, Graduated elsewhere; Pratt Institute of which, as an architect you are probably aware.

Yes, eldartford, Cambridge was an interesting place in the early 60's: Tim Leary, Lou Reed and Andy Warhol (no comment ;-) My 4th floor walk-up was neatly sandwiched between the AR and the KLH factories ;-)

As to acoustic isolation, my expertese is that I actally did a room with the foam insulation sandwiched between sheet rock. I did it for thermal insulation, but was astonished by the acoustic isolation result.

What you did, from a structural/mechanical POV (in addition to the thermal thing) was to construct a (kind of) laminated skin structure (with the styro as a core.) This added considerable stiffness to the wall surface itself, which may account for the increased transmission loss.

Stagered studs have pros and cons. It minimizes direct transmission through the wall, but, with sheetrock on only one side of the studs the walls are not very stiff.

The wall's structural stiffness depends more on a short(er) length/height and larger depth of the studs (6" v. 4") than the stiffness added by the surface material -- unless that skin is stretched/stressed somehow. I think of a stud as a vertical beam -- you don't want it to bend as the sound wave applies pressure against it (via the drywall surface.)
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Nsgarch...I have built many 2X4 interior walls, and they are almost floppy until you get the sheetrock on the second side.

Eldartford -- Nsgarch...I have built many 2X4 interior walls, and they are almost floppy until you get the sheetrock on the second side.

Yes that is so, but it's mainly because the drywall adds a bit of a 'flange' to the stud making it sort of an "T"- or "I"-beam shape in cross-section. Better to use more nails/screws than the code requires too -- doing so helps create the stressed-skin effect I mentioned earlier.

In any case, the main feature of staggered stud construction is the 'decoupling' of one side from the other; I think the improvement in transmission loss far outweighs any stiffness lost by the studs not being double-faced.

If I were starting from scratch, assuming a new wall and 8 - 9 foot ceilings both sides, I'd do 2x4 staggered studs (2x6 plates) and see if that seems enough (before painting ;-) It it wasn't, I'd start adding more drywall. That usually does it.

What I'm saying is, in a typical residential setting, I'd start with the staggered studs, and add from there as necessary. Why? Try changing your mind after a regular wall is up and 'rocked! ;-)
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OK, I'm going to do something I've never done here publicly and state my credentials: I attended grammar school PS 101 Oyster bay and at the age of 19 I suffered a grave disappointment I wanted to go to college but they said I had to graduate grammar school first.So then with hard study I went to medical school at Oxford in England. But it was so foggy over there I got lost and didn't know where I was so I couldn't find my way back to class. So with that I missed a whole semester but I finally did graduate forty in a class of forty and became a doctor. I started a practise but I was so good at medicine I didn't have to practice it, I knew it. I now head a research team experimenting with and trying bringing to market a "dehydrated water" supplement for Olympic athletes but the draw back is to liquefy it you need "WATER". Well I am off {really off} so enjoy your evening all and back to the dry conversation about dry walls and such.

Staggered studs is the most insane thing I've heard from a construction standpoint. Not only would a building inspector frown on this, your electrician would kill you if you ever needed any work done. You couldn't hang anything in that room ever because you couldn't confidently find a stud? You can add extra studs at a staggered rate within your 16's, for that matter, you could even stagger steel studs within wood ones?

Yes, I've built clubs. 18" of concrete won't even stop the problems. Eldaford is correct that you should be 16" on center for studs, period. Keeping speakers from being mounted in any way to a wall will reduce the bass transfer.

Doubling the interior drywall helps. Make sure you tape and mud the first layer, then hit is with a second layer. Stagger the drywall seams and not only screw but also glue the first layer to the studs. Ideally if money, time and space didn't matter, I'd build a double wall with the inside wall completely decoupled from the outer wall, built on rubber seams and a false ceiling too-this is only a pipe dream.