Isolation Wall Confusion

Hi guys, I'm currently in the early planning stage of building a studio and I've got a bit stuck on isolation wall design. I've spent many hours reading through numerous threads on here as well as reading other studio design sources both online and in books and I'm still slightly confused about one aspect of studio isolation wall construction. I understand that building a two leaf, mass -> air -> mass, wall is best for isolation however the part I'm confused on is does this take exterior, already in place walls into consideration? For example, if the exterior walls were made of 100mm thick solid concrete blocks, and then I left an air gap of 150mm and then built a single leaf floating wall, overall if I've understood everything correctly, this should make a double leaf isolation. Is this the correct method or should the exterior concrete walls be ignored and a double leaf wall be created within the room? If this is done however when the room is in use and the exterior wall does in fact play a part in the acoustics, won't it create a triple leaf wall as you'll have mass 1 (exterior concrete block wall) -> air gap -> mass 2 -> air gap -> mass 3?

"I understand that building a two leaf, mass -> air -> mass, wall is best for isolation however the part I'm confused on is does this take exterior, already in place walls into consideration?" Yes, exterior boundaries are always part of the assembly unless sufficient space is placed in-between the existing boundary and the new wall assembly.

Sounds like you have an adequate decoupled double leaf assembly. Some low / medium density insulation will help. Don't compress. Then add as much mass as practical on the inside of the new wall to drive the fundamental low frequency mass-air (spring) -mass frequency down