16" O.C. is standard construction which would be appropriate for common walls in a home. 24" on the interior for a special purpose room (audio) will improve the LF TL. Further with room within room construction, the structural load is less and 16" OC would not be required.
You do want a double top plate if you're going to carry any load...like the interior ceiling joists. I don't know why you'd want 8" base/top plates. The only advantage is wall depth and you're in full control of wall depth building a room within a room.
that question was regarding a staggered stud array...
I typically don't want the drywall resting on the subfloor to allow a gap for a good continuous caulking job.
got it. but resting on the face of the plates is fine?
It's going to couple which is why I prefer a clips/channel or room within a room method.
soffits provide entry points for HVAC, for wiring chases ... always a good thing. I don't use them for lighting (they could be) but down lights in a soffit will not provide adequate lighting to the center of the room.
Would, let's say an 18" suspended ceiling, not offer the same HVAC/chase entry capabilities? I see the advantage of a soffit offering protection from noise leakage/flanking for the HVAC and chase entry points however. On a limited budget it would seem that a suspended ceiling would be a good alternative...lots of ornate plates available for themed ceilings out there. Would also seem to allow for center lighting without having to worry about sealing the cans?
One other question, would the double stud route (room w/in a room) require any bracing b/t the inner and outer room? are there decoupling braces available for such?
Not sure if this would be an above grade install or on the foundation..