Guys - I don't have any specs on the inside out wall other than having built Left Bank entirely with that system.
In fact Left Bank defies theory regarding airlayers etc.
The building I started with is a typical 2 storey US barn. 4 x 2 stud frame with and external cladding made up of 6 x 1/2" hardwood laid vertically with 2 x 1/2" battens over the joins. They had warped in the sun so were not airtight, so I disregarded it as a soundproof wall. I clad it internally with a layer of 5/8" drywall and the ceiling was the same except I put it on RC. I didn't bother with the expense of putting any insulation in the outer wall cavity, (did in the ceiling) so the only insulation was on the back of the internal walls in the air cavity as per inside out walls.
When it was finished I fired up the genelecs in the control room and turned them flat out. Sounded great BTW, still do, and then went outside to see if I could hear them. Once out of the building they immediately dropped in level and when I was around the corner and down the side they had vanished. I then went to the rear and the client was there chatting with the next door neighbour. I chatted with them and then pointed out that the monitors were at full tilt - they could hear nothing. That was way above my expectation - I expected at least low end getting through.
So why?? - I suspect it has to do with the properties of the air gap. In all lab tests the air gap is contained in the structure top and bottom whereas in Left Bank it is open to the whole space above the rooms which is a large airspace because of the angular ceilings. I suspect the sound dissapates into this cavity in preference to going through another mass in the outer drywall, hey but I'm no scientist
any ideas??
BTW I visited Armirel at Left Bank the other day. He loves the studio and adores the genelecs. He said, "mate , I'm no engineer I'm a muso so I just put mikes over instruments, set levels and hit record. I don't need to eq anything cos everthing sounds great." He was right - he played me some of his jazz sessions and they sounded fine. He's had some of OZ's finest jazz musos through the studio. He's also had clients up from Sydney who have worked most of Sydney's major studios. They bought their own Pro Tools setup and they reckoned it was the best studio they'd worked in, they loved it.
We are now talking about a left bank II as he's about to move to a better block of land with better views new house etc.
cheers
john