I just bought a sub to augment my B&W CDM1Ses. During setup, I was astonished to find that the B&Ws excite the lowest room resonance at 31.5 Hz! Equally there's peaks at 63Hz and 126Hz. There are relative low points at c. 45-50Hz and also at 100-110Hz. I've been playing around with speaker and sub positions and I've found that moving the speakers closer to the front wall diminishes the troughs relative to the peeks. I've also been drawing the sub out of the corner, it's actually about 90cm from the left side wall and the front of the sub is about 60cm from the front wall. The sub is positioned just to the left and just behind the left speaker. In the beginning I set the crossover at 30Hz, but I think it's now closer to 70Hz, the markings on the frequency adjustement are (30Hz - min, 180Hz max). I set the gain, originally, on the sub by getting the same reading at 80Hz on the SPL meter from the main speakers and then from the sub. Can anybody give me an idea of what I should move and how I should move it to get the troughs to come up in level ? Short of the Behringer Feedback destroyer, that is. What about the gain setting, less or more ? I know I can fiddle that as much as like and at the end of the day it's a question of taste. For the moment I'm trying to minimise the nulls rather than fight the resonant nodes.