Last Summer, I built a dedicated listening room in my basement. We subdivided a very large rec room. Given spousal restraints, the room's final interior dimensions are only about 13x15, but it is totally built for audio. Since we had to put up two new walls to form the space, I had the contractor use 2x6 lumber rather than the more standard 2x4. This makes the walls thicker and a bit more rigid. Also, I have the walls well insulated with heavy fiberglass insulation. This was primarily for sound-proofing, but it seems to dampen some of the resonance nicely in the room.I probably should have used commercial grade sheetrock. It's thicker and has a higher fire rating. My contractor/friend squawked about it plus the costs were going above budget at that point anyway. Are you going to lay a wood floor in your garage space? I just have thick carpet over the concrete basement floor which seems to work well, but wood could offer some benefits. Other features of the room include a new, dedicated 20 amp power line and hospital grade outlets. I also use Realtraps very liberally in the room. I have floor to ceiling Mondotraps in the corners and several more Minitraps along each wall. I have Sonex 2x2 squares all over the ceiling as well. Having a room I can freely play with, with no WAF to worry about on its interior is a great, continuously variable way to tweak things!