Rehearsal room feasibility

Hello all, first let me say thank you for this excellent resource. I've done a thorough search and some heavy reading of this forum and I feel I understand many of the concepts described, but i'm still a bit confused when i try to put it all together. A building has been made available to me in Queens, NY, and I would like to put a rehearsal studio in it. Since I will probably have different bands in there sometimes that aren't me, (I hit around 90db in my current well treated space,) I'd like to be prepared and have appropriate isolation for some worst case scenarios in the 120-125db region. I understand the basic concepts of MSM, and material density, but i'm uncertain as to how to add these things together, since STC's can't be simply added together, in order to decide whether or not this project is feasible. I would greatly appreciate some help here. The space is a 25'w x 14'h x 70' d empty single story red brick warehouse. the walls appear to be at least 10" thick. Ceiling is a bit tougher to gauge, but looks to be asphalt over wood planking, supported by wooden joists. It is between 2 residential buildings, neither of which share a wall. The one on the left has another minimum 10" red brick wall against the warehouse's left 10" red brick wall, each building is built to support its own upper floors, and roof, respectively. The warehouse is separated from the building at the right by a 4-5' walkway that leads to the building's rear. This space is bricked up with a door at the front. I would like to build the rehearsal studio along the right wall of the warehouse, allowing for a 5' interior corridor at the left, which would give ~5' of airspace inside the building before the wall. This would give the room ~5' of air clearance on either side. So cumulatively between people sleeping on the left and people sleeping on the right, I would have neighbor - 20" red brick - 5' airspace - isolated wall - studio - isolated wall - 10" brick - 5' airspace - 10" brick - neighbor I'm just saying "isolated wall" because i'm not sure yet which design would be necessary. I'm assuming at least: left wall: 5/8" drywall | 5/8" drywall | stud wall | |insulation | ?" airspace | insulation | stud wall | 5/8" drywall | 5/8" drywall right wall: 5/8" drywall | 5/8" drywall | stud wall | |insulation | ?" airspace | 10" brick I could also paint or render the brick walls on either side. I realize the ceiling would also have to match the walls in isolation value, I'm not quite sure what that would require at this point. Question 1: In this situation, is it reasonable to assume that, with properly designed interior isolation, I would be able to hit 120db inside the rooms without annoying the neighbors sleeping in the adjacent buildings? Question 2: Would the above described isolation walls accommodate me? Question 3: How do you go about figuring the isolation value of combined elements in a situation like this? if i have missed anything i will do my absolute best to provide whatever information is needed. thanks so much for your time, -John

basically, build each rehearsal unit to be fully isolated and take advantage of the large air gaps around them to improve the TL. consider putting each room on its own floating floor to avoid problems where structure borne noise (flanking) getting into the residential areas. if you were going to then add another layer of isolation - putting up the 10" brick walls might improve things but could also be very costly versus having fully decoupled rooms. instead, metal stud walls with drywall and then a suspended drywall ceiling over the entire space may be just enough to avoid having voices and other higher freq noises disturb the neighbors.