Voice Coil

A voice coil is a type of linear actuator which consists of a coil surrounded by a permanent magnet. When DC flows through the coil it will move parallel to the surround. Unlike a solenoid, the direction of movement depends on the direction of the current.

Unlike a Ballscrew Jack, there are no gears, threaded rods, or other noisy or failure prone mechanical items.

The Soundfucker uses a dildo mounted on the voice coil actuator of a subwoofer.

See also Voice coil on Wikipedia.