Home theater acoustical treatments need to be at least two inches thick, and preferably four inches thick for decent audio quality. Why? Because one-inch materials only treat sounds down to 1 kHz. Everything down below that is freely bouncing around the walls of the room.
For proper audio imaging and articulation, you need to control sound reflections down to at least 500 Hz, and preferably down to 250 Hz. Remember that the Middle A on a piano keyboard is 440 Hz, and you want to go down to that, at least.
Just as bad, however, is creating an acoustically "dead" room. It is convenient to go in with one of the franchised stretched fabric wall systems to cover up all of the walls in a theater. They are simple, quick, clean, cost-predictable, but very wrong. Read more - full article published in Residential Systems Magazine.