If you take a regular battery and put the postivie end to one connector of the speaker and the negative end to the other side of the speaker the cone will move either up or down (doesn't matter which way, as long as all 4 go the same way). If you reverse the phase / polarity of the subwoofer, the door woofers are no longer fighting against the subwoofer pressure. When speakers are operating out of phase the cones mirror each other and the resulting sound is reduced greatly. The difference is heard when one speaker (L or R) is wired correctly, and the other isn't. Put the speakers face to face, with the amp in mono and turn the balance control -- if the bass disappears, they are out of phase. So as long as you know the polarity from the HU the rest is easy, if you don't find the manual online. Its actually not always the easiest thing to tell if you have correct polarity checking with the speakers in their normal positions in the listening room -- reflections and unequal path lengths to your ear etc can cause confusion. This effect - stronger at lower frequencies - will result in a loss of bass. Both speakers and amp outputs have + and - terminals so that the phase is maintained. The effect is much more noticed at the lower "Bass" frequencies. One will move in, while the other moves out. If the input applied to several speakers wired with mixed polarity, it puts them "out of phase" with each other, meaning that while one speaker moves "in" the other move "out" and therefore create distortions in the resulting sound. At the listening position (right in between the speakers) the displaced air from one will be cancelled out by the other. You won't hear a difference in polarity because there isn't any. When polarity is wrong, the speakers will be out of phase. In fact the subwoofer reverse pulse actually creates less pressure and the midwoofers breathe easier. Speaker polarity then becomes a very important parameter to check. Polarity is the right word. Bottom line- you get more midbass and sub-bass when the sub is reverse polarity.