Higher coil mass, sensitivity low to medium.‡ Soft non-linearity as the coil exceeds limits. Underhung coil Gap's height is greater than the coil's height. This method keeps the magnetic flux that the coil experiences, constant over the coil's normal excursion range. Low coil mass, sensitivity medium to high.‡ Hard non-linearity as the coil exceeds limits. Both topologies attempt the same goal: linear force acting on the coil, for a driver that reproduces the applied signal faithfully. Other uses for the term The term "voice coil" has been generalized and refers to any galvanometer-like mechanism that uses a solenoid to move an object back-and-forth within a magnetic field. In particular, it is commonly used to refer to the coil of wire that moves the read–write heads in a moving-head disk drive. In this application, a very lightweight coil of wires is mounted within a strong magnetic field produced by permanent rare-earth magnets. The voice coil is the motor part of the servo system that positions the heads: an electric control signal drives the voice coil and the resulting force quickly and accurately positions the heads. See also Galvanometer References , A good paper on Voice Coil Actuators. The Hisco Loudspeaker Voice Coil Handbook, 7th Edition, August 2001. Hisco, Anaheim, CA 92807. 714 777 2665. Voice Coil Actuators, Principle and Practice. Electromagnetic coils Loudspeakers