Air Cavity??

I am new to this forum and have been reading back posts. The diagram John posted on Sun Mar 02, 2003 is a real eye opener. One would have thought that two completely separate walls, faced on both sides and built on separate floating floors (that is how I am interpreting the double isolated stud, STC 40, example) would have performed better!? So much for common sense. Regarding the STC 63 example, do the two stud walls rest on one bottom (sole) plate and have one, common top plate? Or do the two stud walls have separate plates? I can't get my mind around this, so I clearly am not understanding something. In the former case, the plates would have to be at least 8 inches wide and would sit on both of the floating floors (assuming the walls were build on the floors). doesn't seem right to connect the floors in this manner. Also to get more than a very small space between stud walls, the width would have to go up from 8 inches. But in the later case, the air cavity between the stud walls would be all the "free" air space in the studio (ie, all the space not inclosed by the stud walls- all the space outside of the control room, live room, isos, etc.) because the stud walls, being open between them at top and bottom, form a channel connecting all non-enclosed space in the studio. This doesn't seem right either (very odd spring). Like I said, I am not understanding something hear. Some one please steer my out of the woods. Thank you.

First, the 63 dB example uses separate frames entirely - their only connection to each other would be if both were sitting on the same floor, in which case if they are wood frames you would benefit by a few dB if Resilient Channel were used on one side. The wierd spring you refer to (all that air) is a GOOD thing - factors that improve isolation (assuming you're sticking to the proven mass-spring-mass model of a 2-leaf wall) are more mass, wider air space (softer spring), decoupling between leaves , stiffer leaf (better bass rejection) proper density of insulation between leaves (2.5-3 PCF is considered optimum for music), insulation touching at least one inner panel (damping improves Transmission Loss), there are probably others I've missed but those are the main ones. Best isolation overall is to completely float each room, with separate frames for each leaf - one frame on one floated floor with one leaf (multi layer, different thicknesses in layers) (the other leaf in that wall would be on the other floated floor)- then, suspending ceilings inside the walls using isolators on each suspension wire. All this is a waste of time unless you use double doors with an air lock between rooms, because any openable partition takes a lot more work to achieve those levels of isolation so you need two in tandem, the more air space between them the better - it also helps to put lots of absorbent in the air lock. Hope that cleared up some of your questions... Steve