meta, if yer wall is only 4' behind ya, i'd suggest absorbers extending at least 3' either side of the *sweet-spot*. if the wall is a bit further back, but still in the vicinity, then i'd go w/diffusors. if ya got lotsa room behind ya (i'm fortunate to have >20'), then i am a follower of the *dead-end/live-end* room set-up, where the walls to the sides of, & behind the speakers are *dead*, ie - w/absorbers & diffusers, and the walls in front of the speakers are *live*. my only mod to this would be to place absorbers at the 1st-reflection-point to the listening position along the side-walls, if they are close to the speakers.
doug s.