I treated my ceiling like I did my side walls for a high end 2 channel system in 4000 cubic feet space. The floor is carpeted. Lastly, the speakers are pulled out from the front wall with scatter plates behind them. Bass absorbers are inserted in the front corners. Locations for the admixture of absorption and reflection panels were determined based on 1st and 2nd reflections. The sound detail is magnificent, because the structural boundaries have disappeared — especially for depth of the sound stage. I found that strong equipment is made better by sound treatment of the listening space.
Treating the ceiling and floor, who else has had great results?
Two areas of the room often neglected by audiophiles IMHO is the ceiling and floor. We focus so much on first reflections we forget about overall energy left in a room after the speaker has stopped.
I've had excellent luck with treating the ceiling, especially for home theater applications, and this was before Atmos. The area behind the speakers near the floor often hides noise and distortion which we didn't know we were hearing. Throw a blanket over there and listen for yourself.
Who else has gone through the trouble of treating their ceiling?