Wireless Outdoor Speakers

The coil is oriented coaxially inside the gap, a small circular volume (a hole, slot, or groove) in the magnetic structure within which it can move back and forth. The gap establishes a concentrated magnetic field between the two poles of a permanent magnet; the outside of the gap being one pole and the center post (a.k.a., the pole-piece) being the other. The center post and back-plate are sometimes a single piece called the yoke.

An audio engineering rule of thumb is that individual electrodynamic drivers provide quality performance over at most about 3 octaves. Multiple drivers (i.e., subwoofers, woofers, mid-range drivers, tweeters) are generally used in a complete loudspeaker system to provide performance beyond 3 octaves.