What's phase 0 degree - 180 degree?

Yo Worldcup86, Phase in simple terms is the direction a driver cone is moving relative to the electrical signal being sent to it. In a perfect world, all the drivers in a speaker system would move out at the same time and in at the same time. That way they would be "in phase" with each other. But in the real world, we have crossovers (inside the speakers) that change the phase angle of the various drivers relative to each other. In extreme cases, if the phase angle between two drivers is 180 degrees apart, then they will cancel each other out at overlapping frequencies. This will cause a dip in the frequency response in the region where the crossover point is. Depending on how low your main speakers will go and where you set the rollover frequency on the sub, this region can be fairly large or very small. Lets suppose that your main speakers put out bass down to 50hz. and you want to achieve the flattest frequency response possible. If you set the sub crossover point to 40-45hz then the sub will be rolling off about 3db (half as loud) at 50hz. The main speakers will be rolling of about the same amount and you'll have enough overlap that you shouldn't have a big bump or a big dip at 40-50hz but this is also quite dependent on the room characteristics and sub placement. Once you have the crossover point set, then you can experiment with phase setting. Ideally, you want the cone of the sub moving out (toward the room) when a bass note, gunshot, explosion, or any other loud sound occurs. That will provide the most "felt" impact. If the cone is moving in (away from the room) then the air in the room is not compressed at the right time and some of the effect is lost. Once you get the sub in phase, then the main speakers need to be checked as well. You can change the phase by reversing the speaker wires (red on black) if you need to.