Buy a TacT Room Correction System preamp and forget the room treatments. In the long run, it's cheaper and more effective.
Where to start with room acoustics
I just moved into a new house that has a listening room (13 ft x 27ft with 8 1/2 ft ceiling). It is obvious the room needs some help. I have read some of the chapters in Master Handbook of Acoustics by Everest (although some of it is over my head). The question is how to assess the needs for this room. Where should I start?