Hi! I have been slowly working on building out a new room in my basement for practicing/recording drums. It's been a slow process, that has thus far involved removing water heaters, and breaking up the concrete floor to re-route the water main so that I have a relatively unobstructed floor space to work with. I have about 8' 4" from floor to the bottom of the ceiling joists, and about 11 1/2' x 14' of space to work with. As a side note, the rest of the basement is finished, and the lovely wife isn't wild about me tearing that stuff apart as I do my build. I have started beefing up the existing subfloor above my space using 'rods method' of adding two layers of 5/8 drywall between the joists, with green glue, and then battening them into place with 1x2. My plan is to build the 'room in a room' and have a new "inner ceiling" supported by the new framing I build. In the picture attached you can see what I have going on thus far. My questions are: In the attached picture, you can see a space (labeled A). On the other side of that is the brick veneer of my home. If I seal that area up with drywall and acoustic sealant, am I essentially creating a small 3-leaf system once I have my drum rooms walls built? Should I fill that cavity with layers of drywall? just insulation? Or is it such a small space that I shouldn't be fretting about three leaves? Also, Above this ceiling is our 'formal' dining room (not used much). In the space labeled "B" you can see the ductwork feeding the vents in that dining room. Keeping in mind that I AM going to be building that decoupled "inner" ceiling, what should I do about that duct and vent feeding the dining room?