I would just like to comment on how beneficial I have found DIY acoustic panels to be in my theater room. I was skeptical at first and had no expectations.... I would highly recommend them to anyone looking for a fun project for little $ and big impact.
I was careful to set up the mains first to get the soundstage/imaging as best I could. All room EQ was, and remains off. The speakers were not moved once initially set.
I used Roxul Safe n' sound 23" x 47" x 3" batts vertically at first reflection points (mirror on wall) and half width panels in the front upper corners of the room for bass traps. At first I included a panel horizontally directly behind the listening position, but soon found out that doing so removed the spaciousness of the sound; artificially shrinking the rooms feel-- especially noticalbe in vocals. Treating the back wall for me deadened/flattened the sound considerably.
I used 2ch music my testing, as I find it to be pretty telling of absolute potential of the system. If music sounds great, movies will be great as well.
I thought it sounded great. Stereo music was full, enveloping and almost holographic in the way the center image was formed while instruments and drums bounced around the singer. CDs had a live sound and the vocals were pushed noticably forward into the room.
All the above plus:
I heard much, much more detail than I had ever heard out of CDs than I was accustomed to. The speakers themselves dissapeared more and were hard (if not impossible) to pinpoint with my eyes closed. The sound became a wall of energy with a stronger illusion of players spaced on a full stage. I never knew how much reverb my room added before I heard it treated. Instruments, particularly horns and percussion sounded much more focused and sharp.
-Added detail and clarity in vocals and instruments
-Micro details like singers breathing and lips were now noticable when not present before
-Every song I listened to made me appreciate how well (or not) the track was mixed and how much time must have been spent on pouring over every little detail
-Large improvement for little $
-Flaws revealed: Poorly recorded, compressed or mixed tracks sound much worse.
-any noise floor in the track is noticable
-Not all details in songs are meant to be heard (in one track I could hear people faintly talking in the background...groupies?)
-Easy to over dampen sound. Go slowly and listen as you proceed.
-Picking fabric can be a tedious process. Avoid shimmer. Matte fabrics hide imperfections in acoustic material.
In my experience the level of detail/clarity possible from a good setup can become much improved if acoustic panels are used to tame first and secondary reflections. It's not going to make poor speakers sound great, but will help good speakers deliver their potential. I would encourage anyone to experiment with treatments and enjoy the difference.