10x18 room, speakers at short wall, bass traps in corners, 2x4 panels and 2x4 mondo traps cover rear wall and side wall to sitting position. Throw rug on wood floor. Great sounstage (see systems) Awesome vocals, incredible seperation and holography.
Problem is I cant get the sound to come down the side walls more than a foot or two beyond speakers. I sit outer edge of equalateral triangle. Do I need to cover more wall behind me?
I have a great deal of sympathy with your dilemma as I'm having a very similar problem now, speaker placement in a small room. Oddly enough, to get images beyond the width of the speakers, you need long period reflections from the side wall. However early reflections in your present room placement are highly detrimental to the rest of the soundstage. I have to second Wayne's suggestion of long wall placement, or an imitation of it. So without changing the room around, move the seat closer (80% of the speaker spread) and experiment with toe in. Toe in can either be crossing behind your head a couple of feet, or crossing several feet in front of your seat. Use the same formulas if you're willing to try the long wall placement, fairly near-field listening is about the only option in a small room, so I would embrace it rather than trying to recreate a large room placement.
As far as room treatments, add diffusers to the rear wall, not absorptive panels. Or you might try replacing your side wall absorptive panels for diffusers. The room looks fairly live, you'd want to break up as many reflection modes as possible.
P.S. +2 on the Audio Physic site. They have this one and an older page no longer on their site but copied on several internet sites. Both are primarily focused on early reflection reduction by speaker and listening seat position, with room treatments a fill in for areas that cannot be addressed with this.
