Moving iron speaker

Electromagnetic speakers were frequently used in the early days of audio technology, meanwhile, but no more.

In the electromagnetic speaker is moved either an iron membrane, which radiates sound directly (see sketch), or enclosed by a coil iron rod swings before the air gap of a permanent magnet and is connected to a paper cone. Such speakers are no longer built today. A superimposed DC field and the LF- field drives a ferromagnetic membrane.

The disadvantages of these structures are:

• High harmonic distortion, since the force to a distance-dependent and the other is not linear, but quadratic depends on the current,
• Unsuitable, heavy, resonant material for membrane or iron rod necessary, resulting in a tinny sound.
• Even at rest, a force must be applied, so the swinging iron part ( membrane or iron rod) must be hard and rigid, resulting in poor low-frequency ( high resonance frequency due to high stiffness) and treble ( high mass ) results.

This principle is also used in magnetic and electromagnetic microphones, headphones (both obsolete), as well as used in telephone answering shells. The principle is reversed, however, is still used in electromagnetic (Moving Iron ) Schallplattenabtastern (MI).