I have my first two bass traps up and absorbing which you can see from the pictures in my previous post. I was listening to a YOYO MA duet with piano while completing the assembly in the music / HT room. After placing the first trap in its corner behind the speaker I sat down in my normal listening spot. I was amazed that the piano and cello had seem to have disappeared from any part of the sound stage on the side with the trap. It was as if I was playing only the left channel. I walked up to the right speaker to be sure it was still playing. I was startled (I will probably use startled and amazed a lot in this message, sorry) by how much absorption the trap had. I finished the second trap and put it in place. Upon returning to my seat the sound stage had returned across the full front. The sound stage was as broad as before but it seemed to have much more depth, something I had not expected. After playing a few other pieces of music it was obvious that to much of the mid-high frequency was being absorbed as nothing was quite as clear, crisp and pronounced as before. It was quite obvious how much rear reflection I was hearing from the Martin Logan sl3's. I doubt if it would have affected a non-dipole speaker as much. During the week I played with covering the face of the cotton with different size pieces of brown craft paper. I started with complete coverage. It sounded better but the depth of sound stage had shrunk. So far have settled on half the width of the front face top to bottom but with the paper moved to the left side on the right trap and the right side of the left trap. It seems to allow sound directly behind the ML to reflect some what but still absorbs much of the sound. I even played with adjusting the tilt of the 2 1/2" horizontal blinds on the front wall behind the traps and speakers and was surprised how it would affect the sound.
I have always though most all speakers have way to much bass for my liking listening to music. My Aragon preamp is from the world of, here is the music you don't get tone controls change your room. The bass had tightened up alot to where is was quite pleasing. I didn't know what to expect from the traps so hearing bass I enjoyed was a nice change.
Another thing I had not expected was the increased depth of sound the was coming from the right side of the right speaker and the left side of the left speaker. I have always been puzzled by the ability of a speaker to appear to produce sound not from in front of or between two speakers but from what seems to be well outside of the speakers physical position. It was very pleasing to have the music change that much. I was listening to a piece by Sarah McLachlan where here piano had to have been open and more than one mic for the recording because swear I could hear sound from the strings from up close to a few feet behind it depending on where in the piano the string was located.
I have listened to more music this last week than I had in the last 2 years. Simply because the sound was so improved. Each time I would sit down and the music would start I was shocked that this was the same equipment I had been listening to for the last 4 years. I also choose to do more music than movies at first because the current HT setup is fairly new and my listening reference base to how the music had sounded was greater. In the past I would start listening to rock music (which I enjoy) and after 10 min or so I would start skipping to tracks I really wanted to hear because it often seemed to noisy (if that makes any sense) but now I think it was more a problem of room reflections that made it unpleasant at times. It was great to sit and listen to some early Doors and Led Zeppelin again, it was a totally new listening experience.
As far as movie watching which was why I was installing the traps in the first place the room has lost much of the boomyness that we didn't like, but there is still more than enough low end to shake the room, startle you and scare the deer away outside. I re-played the chase scene from Batman Begins and the low end made your body react but what sometimes felt like your ears needed to pop to clear themselves has been removed I just can't believe that adding the 2 traps can improve the sound as much as it has.
With that much improvement I decided to improve the anchoring of my front L & R and subwoofers to the floor through the carpeting. I glued 3 pieces of 3/4" MDF together to make a 2 1/4" thick base and made long spikes to go through the carpet and pad. I could then stand on the base and be sure the spikes penetrated the plywood underlayment. I then set the speakers with their spikes on the bases. This is probably the first time my speakers have been really anchored to the floor. This also has helped make the bass a little tighter.

My wife is a kind of a "give me one speaker that doesn't sound terrible and I can listen to music I want and I'm happy" type listener. She was impressed enough with the calming of the bass in movies that when at the best possible moment when we were watching a movie I took a deep breath and said " I think I am going to build 2 more traps for the back corners of the room. You don't mind if I move one of the bookcases that are in the corner where one trap would go do you". She looked at the front traps looked at the back corners looked at me and said " that large?" Feeling the tide shifting in my favor I bravely said "Ya you won't really notice them once I cover them with fabric to match the walls. Don't the 4 large rear and side surround speakers blend in now that they match the wall color?" She looked at them and said "No they don't but as long as they (the other 2 traps) don't block the cross ventilation and that's what you want that's fine".
So I will be ordering more cotton from Bryan at Sensible Sound Solutions he seems to be happy to answer question and offer suggestions.

Sorry if this rambled on but I am truly suppried
at the difference. I had read post on forums from people who proclaimed the virtues of bass traps and finally decided to give them a try. My cost so far is about $200 for the two traps.
As I think Doug suggented in another post here think of it as just another piece of equipment you are adding, You won't be dissapointed I'm sure.

Brad