Driver

Any of the moving elements that turn signal into sound — woofer, midrange, tweeter.

A driver is the motor-and-diaphragm assembly that moves air: a voice coil in a magnetic gap pushes a cone or dome. Woofers handle lows, midranges the middle, tweeters the top; a crossover divides the signal among them. Driver count and quality set what a speaker can do; the cabinet and crossover decide whether it does it cleanly.