Electrodynamic loudspeaker

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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.[dubious ]

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.

While now uncommon, electrodynamic loudspeakers were once common in top quality mantel radios and similar domestic audio applications, particularly in the post-war period of World War II. In these appliances the field coil of the loudspeaker was also used as the main or only filter choke in the high tension power supply to the valve anodes.

Advances in permanent magnet technology rendered the traditional electrodynamic loudspeaker obsolete. The type survives in some high-end hi-fi applications.

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