MOVING IRON LOUDSPEAKER, 1920's
Before permanent magnets were made strong enough and cheap enough, loudspeakers used a coil moving an iron reed which was attached to the diaphragm of the speaker.
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Internally a high resistance coil with a permanent magnet through it was used to move an iron reed, attached to a rod on which was placed the paper cone. An Adjustment was provided for maximum efficiency. This method did not require a strong magnet to operate, and the quality was inferior to modern loudspeakers which use the moving coil principal.