Two quick questions... First the situation is I'm moving my room and all my HT components from the 2nd bedroom of my apartment to the larger first bedroom. Nice thing about my little 2nd room was it wasn't bordering any other units, but the new room is. By code my apartment and the one next door is bordered by 4 layers of 5/8" sheetrock (firewall), which is a decent sound barrier as it is. BTW the room I'm bordering is a bedroom next door, isolation is a must, and insulating inside the walls isn't possible. What I'm considering is adding an additional layer of 5/8" sheetrock to that bordering wall. Question is... am I wasting my time cause it'll have to be installed, floated, primed and painted... or is it going to be too little improvement to even worry about doing all that work. One thing we can all agree on is it can't hurt. I even considered perhaps putting a thin layer of foam in between the old rock and new layer to help out. Second questions is this: The subfloor is concrete. That steel reinforced concrete which the whole building is made out of allows sound to travel easy, particularlly banging, knocking, and booming sounds (like a Subwoofer). What I'm considering doing is liquid nailing a layer of 3/4" plywood and putting carpet over that. Again, I ask... pros/cons of this. Will it do any good, or am I wasting my time. Any alternatives are welcome. Thnkas everyone for reading and any help you can offer.