I am a bit confuse, while most speaker crossover design connect all speaker negative post togheter, one of mine connect the woofer in reverse polarity. This result in a DC out of phase with my other speaker in the room. A coil is in serie with the woofer, so I must assume that this cause a 90 phase shift in lower frequency, still the woofer will still be out of phase with the other. Can someone clarified the reason why the woofer is reverse on that particular crossover? My problem is that those two speaker boxes are no longer use stand alone, they are part of a 5.1 system and the bass level is far than be satisfaying, I think the main woofer been out of phase with the subwoofer cause that lack of bass reponse. Using the two main speaker alone is working fine, but now that they are assited by the subwoofer, bass level tend to be inferior than before. I check the output of the main amplifiers with a scope in regard to a tone at the input. While the output is not in phase with the input, the left, right, center and sub are nearly in phase, just the sub that is slighly out of phase, probably because of the active filter involve, both surround speaker are 180 degree out of phase. So the only problem can only originate in the speaker crossover, so I reverse the polarity of the main speaker just to check, I not sure, but I think bass level improve, so should I keep the main left & right speaker in reverse to match the other?