Double width studs for isolation?

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.

L, If you are considering 12 inch center framing, you are on the right track. 2 layers of 5/8 works wonders. Do stagger the joints in both directions. I use 6 inch acoustic insulation in 3 1/2 framing. Also works wonders. You do need both sides of this wall sheetrocked. 1/2 on the other side is fine. Hold the board 1/2 off the floor and 1/2 down from the lid, then fill this void with acousical sealant.

Schipo, I always tell people that every medical class has someone who graduated last, and that person just might be THEIR doctor.

Anyway, builders of townhomes with shared walls often put a "double" or "staggered" wall between units to minimize sound transmission.

If you put some fuzzy stuff between the studs, companies such as Roxul or Corning make insulation with sound absorbing properties. You can find it at Home Depot.

Also, I've never seen it in a store, but on some home reno shows on HGTV, I've seen a new type of sound absorbing drywall. It's a bit expensive. I believe it has a sheet of metal sandwiched between layers of gypsum. It might work through the stiffening effect that Nsgach noted. Maybe you can find it somewhere. Try the websites for drywall manufacturers.

Eldartford is correct about the styrofoam stuff having to be covered to avoid fires. I'm finishing my basement and I'm looking at adding styrofoam or polystyrene panels on the wall as a thermal break and for insulation. The panels all say that they need to be covered with something because they are flammable. The building code where I live requires covering as well.

I'm not smart enough to go to MIT. Maybe some of what I'm saying is true anyway.