[nodiak]

Room: 11.5' x 7.5' x 26.5'. Speakers 5-6' out on short wall , ~ 2.5' from sides. I have had 5" thick, 24" x 90" bass traps in each front wall corner. Took me a week or so to get used to the positive effect it was having, as I was conditioned to decades of echoes and bass lift. They helped stabilized the music, keeping the soundstage more firmly in place. Midrange became fuller, bass tightened up some, and the shrill highs diminished.
This morning I finally got around to putting up another piece horizontally along the front wall/ceiling intersection. It's a narrower piece at 12", but is set at ~ 45 degree angle and so has several inches space behind it. It is wrapped in burlap, and framed with basic 2" x 2" fir (functional, could be made nicer). It's 90" length allows 6" of bare wall before the edges of the corner traps.
Sorry no camera.
Anyway, the point is this made a pretty big difference, more of the same. Especially tighter bass, made me turn down the sub, and get much better quality. Another level of soundstage stability. More midrange weight. The shrill highs taken down another notch. The effect is I can turn the music louder before the room problems start to win. That threshold is raised.
I'm using 5" cotton Bass Buster I got from Bryan. It's working great for me.
I have some more and want to continue do a section on the ceiling between speakers and main seat. Should have enough to put two more small ones at angles on wall/ceiling intersections on side walls behind speakers.

Last week I put up skyline type diffusers on the upper corners of the rear wall (it is ~ 10' behind listening seat). They are homemade out of 2" x 2" fir. Heavy, so I screwed them into 2 x 4 studs and the studs into the wall framing. The effect was mild. It seemed to smooth the music out a bit, especially when hanging around the rear of the room near them. But maybe that's a psyche out cause we like their looks!

The treatments are really transforming things. Thanks to Bryan, Ethan, etc. for the helpful ideas! Going good (but slow) here. 

Don     

[bpape]

Congrats!  Those center front and rear wall/ceiling corners can really make a difference.  Many people don't want to do that for aesthetic reasons but it's an excellent piece of the treatment puzzle.

Bryan

[nodiak]

Added the last 24" x 96" piece of 5" bass buster horizontaly against the front wall at the floor level. I just started using dipole speakers again and much of the rearwave reflections get eaten up with this. The speakers are 5' out from the front wall. Not much noticeable effect on the bass, but easily heard on the mids and highs of the dipole's rearwave. More solid imaging and stable soundstage.
I'll need to get more absorbant and do the reflection points of walls and ceiling in the middle of the room.
Don