Three-leaf questions

OK, this is a hypothetical question here, but will someday (sigh) be important in designing my studio. I hope. So, 3-leaf construction is bad. I get that vibe from all the other posts. I also dig that each situation is completely unique, and that all answers around here are to be taken as advice, not rules, unless well-detailed, specific plans were posted along with the questions. Now for the questions. #1 - I've seen it mentioned that a cinderblock wall, without mortar or sand filling it in, is essentially a 2-leaf construction. Is this a situation wherein having a 3-leaf system is unavoidable, and probably even preferable? #2 - I'm in a city with lots of empty warehouses, and one of them will hopefully eventually house my studio. Given a large enough space, I have it in my mind to build a hallway or closets around the entire perimeter of the studio part, giving at least 4' of air between the outside world and the outer wall of the studio rooms. I've read here that a 3rd leaf can be extremely detrimental to the overall STC of a structure. Should the internal studio walls then be approached as an independant 2-leaf structure, or would it need to be considered as a 3-leaf, with the exterior wall being the third? Transmission between the studio and the hallway would be important, but not nearly as important as transmission to/from outside. That's it for now, I think...thanks in advance! MPEDrummer

Ok, one more... I just read in another post that there's not much benefit to more air beyond about 12"? Is that correct? Does that mean in question 2 above, the exterior wall would be far enough away to be considered as its own structure, and not a 3rd leaf? MPEDrummer

Yes. A wall, a very large airgap and then a double leaf construction isn't very bad. STC is a worthless standard for isolating sound with a music spectrum. STC is about mid frequencies, and a triple leaf wall can be better for such a spectrum. For music, the lower frequencies are dictating TL, and then a triple leaf construction isn't good. But with a 120 cm airgap you should be save.

Excellent. I feel like I'm this close to actually getting all this stuff. It's been far too long since my acoustics classes in college. Thanks! MPEDrummer