The diaphragms of moving coil loudspeakers are liable to drift from the zero position and jump out at high amplitudes, owing to the magnetic leakage field. The drive force (flux-linked turns) is not constant with voice coil position, even with very long coils, but is a maximum at the zero position and falls off on either side. In the mass-controlled region, the coil drifts towards the weaker field, i.e. it is fundamentally unstable. This is the major cause of distortion in moving coil loudspeakers.
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