i used Owens Corning 703 rigid fiberglass panels (2'X4'X2") wrapped in burlap. Placed 4" thick on ceiling and side wall first reflection points - 2" airgap... all the corner panels are 6" deep. I wanted to try some diffusion at the back of the room but didn't quite have enough depth in the room to make them efficient - so I covered 1/2 of the back wall and all corners with similar absorbing panels. I treated the room simply because of what I read how it should help the sound...but what made me a believer was when I (reluctantly) treated the first reflection point on the ceiling...I originally only treated the area over one speaker to compare... and that speaker really came alive - clear/tight/focused! (The rigid fiberglass is real easy to work with...if you can wrap a Christmas present and use a hot glue gun you can make an absorbing panel...I treated the whole room for about $400... )