There are several good products that can be purchased locally to insulate your HT room. One of the most effective items is to make sure that you use resilient channelt to mount the wall board. Resiliant channel isolates the wall boards from the studs eliminating the transmission of sound to the frame work. You can use this to mount all the wall board, ceilings & walls, the better the isolation the better the sound damping will be. I also stuffed all the walls and the ceiling with Rouxal safe and sound, this is a very dense mineral fibre product. The combination of the channel and the rouxal has made a huge difference in my HT room. Even at very loud volumes you cannot hear anything but the lowest frequencies even in the rooms directly above my system.
