Both voltages may be either positive or negative when referenced to the potential of the earth which, by the way, may not be resting at zero with respect to the universe. Phase is a term that is implicitly linked to an ongoing time sequence of two or more series of events as observed relative to some common reference point in time. The measure of the difference in phase is always expressed as a time relation, be it in terms of actual seconds, minutes, hours, etc., or as relative time in terms of increments or fractions of complete cycles of events, such as in units of degrees or radians. It is clear that two or more events may be precisely in phase with one another while being of either positive or negative polarity. Phase and polarity are related although one is not precisely identical to the other.
Most manufacturers indicate with colored binding posts a difference between the speaker terminals.
Unfortunately, inconsistent or incorrect polarity distinction is quite common, partly due to erratic quality control and the fact that some manufacturers wire their elements opposite to other manufacturers. When the speaker leads touch the battery terminal, the cone will move in or out. If it moves out the terminal touching the positive side of the battery is positive in that it condenses the air. If the cone moves in then the terminals are reversed. The negative side of the battery is connected to the positive side of the speaker causing the cone to rarefy.