I have been tweaking out my room, which is rather large, about 27(L) x 22(W) x 10(H) and has various 50 degree angles from about the half way point on the walls up to the ceiling as its built over a garage. Right now its standard drywall treatment, with carpet. Given its odd shape, I'm not quite sure what to do about my problem, which is: I appear to have a mode at 71Hz, as you hear nothing at that frequency, which is about -16dB. However, from about 55Hz to 90Hz there is also a substantial bell shaped dip, centering on 71Hz with a 6dB peak again at around 109 or so, and another bell shaped dip of -6dB around 138Hz, which from what I know, seems to make some sense. I've moved my speakers all around the room on a rolling cart trying all covceivable positions, and located one spot where the dips were less, but probably not a practicle position to monitor from. They are the HR824s, and I've got them with switches positioned at 47Hz, acoustic space B, and the "0" position for the highend. However, the problem areas do not seem to be effected very much by any switch combination. I know these have been debated endlessly elsewhere on the forum, and despite that, I own them and I don't want to re-debate them. The response from them is otherwise reasonably flat, within ± 2dB above 300Hz to about 19K. AND....I have measured them with precision to make sure they are centered and at various equal distances from the rear wall. Nothing seems to make a difference. So what are my solutions to this problem? I'm a bit thrown by the odd nature of the sloped ceilings.