Soundproofing 101

So the studio is coming along slowly. We have the largest of the soundproofing walls completely framed. The two foot top sections (trusses) take about 5 times as long as the rest of the wall, because we more or less have to be exact in our measurements for the wall to stand straight and have a tight seal against the blocks and rubber that decouple them from the floor and ceiling.
The idea is to build a very dense wall inside the existing wall to cut down the STC or sound transmission coefficient to practically zero at high and mid frequencies and to reduce low end transmission to negligible amounts. To accomplish that we place a layer of highly absorptive foam rubber over the studs and conventional insulation, then two sheets of drywall, and a rigid fiberglass product generically called 703 covered with fabric. So after passing through an inch of rigid fiberglass, 1 and a quarter inches of sheetrock, 6 millimeters of high density foam rubber, 7 inches of packed fiberglass insulation, and another half inch of sheetrock, the amplitude of the sound waves has died enough that 2 feet of dead air and a conventional wall will do the rest. The hardest thing is that we really will have no idea how much we've reduced the STC till the wall is finished and we place a drum set or guitar amp inside and rock out.