Originally Posted by m. zillch
Comparing the motion of the woofers to the microphone diaphragm which recorded the music, that's called absolute phase, aka polarity.
Minor point of clarification. I didn't mean to imply only electro-acoustical transducers* have polarity. In audio, any
device which has both an input and an output has the potential to flip the polarity as it passes through the device, aka "inverting the polarity", so EQs, AVRs, powered subwoofers, tape recorders, etc. also have a polarity. [Unless specified otherwise, one assumes, or hopes, that it is normal, aka "non-inverting"]
To the human ear it usually doesn't matter, unless
two or more devices with alternate polarity are used together and mixed: this is for example why both L and R speakers, or say both subwoofers, need to be in the same
phase so when their sound waves collide in the air they amplify each other rather than cancel each other out.
*a transducer is a device which takes one form of energy and transforms it into another. Electro-acoustical ones move energy between the electrical domain, a voltage, and the acoustical domain, a sound wave in the air. Microphones and speakers are the two main ones of these.