Electrodynamic loudspeaker

An electrodynamic loudspeaker or field coil loudspeaker is a dynamic loudspeaker in which the field is produced by an electromagnet rather than by a permanent magnet.

An electrodynamic loudspeaker therefore has two coils:

The first electrodynamic loudspeakers were produced in the 1930s, to address the problem that strong permanent magnets of the time were extremely heavy. A compromise was therefore necessary between loudspeaker efficiency, which required the strongest possible magnet, and weight. The use of a strong but relatively light electromagnet solved this problem.