I was just wondering what the theory/science behind the phase control setting on the sub. When I try to calibrate the sub using this control, the manual says to turn the phase control, starting from zero degrees, until you hear the greatest quantity of bass output. However, the setting seems very subtle. I have a servo-15 and borrowed a friends x-30 crossover. Why does adjusting the phase control allow the sub to increase it's bass output? Since the servo-15 does not have a phase control on board, is the use of this control necessary since I only heard a subtle difference? I really had to strain to hear a difference. I understand if the explanation is very long and complicated so links would be fine if anyone knows of any. Thanks.