Proper Room Acoustics/Designs

I'm no expert, but I took a quick look at Dennis' wall construction and I'm not sure all this is needed to build a very good sounding room. Unless you're also very concerned about sound getting out of the room, a room within a room may not even be necessary. Seems to me a couple slabs of Sheetrock sandwiched together with something like Green Glue and then attached to the studs using resilient channels (all very cheap by the way) may accomplish much the same thing without having to do all that extra construction and/or having to buy all those presumably expensive charcoal bass traps and diffusers. I'm not saying Dennis doesn't know his stuff or that his method doesn't work, but also consider he's in the business of selling sound absorption products and there are other proven ways to go. As I mentioned on your other post, read Premium Home Theater by Earl Geddes -- invaluable information to know regarding room design and sound optimization, and I consider it a must read before taking on a project of this magnitude.

Yeah, since bass seems to be your biggest issue I'd have concerns over the proposed design. The double drywall will do little or nothing to absorb long bass waves, which means they will continue to be reflected back into your room. Secondly, since the bass diffusers are located behind the double drywall I don't see how they could solve a problem that would already have occurred inside your room. Seems like that design would possibly help reduce transmitting bass outside (or outside sound getting into) your room but not do much for the sound inside your room.