We have a local autosound place in town. They carry a no-name brand "tar paper like" sound dampening material, that is about 1/8" thick, sticky on one side, and I believe, 30" width. It's affordable, (compare to Deflex or other name brands), and works quite well to stop wall reflections. Check around @ those kind of shops. You'll still need some kind of stuffing if it's an enclosed or ported cabinet.