Voice coil originally described the coil of copper wire mounted to the moving cone of a loudspeaker. By applying a voltage to the voice coil, a magnetic field was produced. This magnetic field would be cause the voice coil to be attracted to or repelled from a magnet fixed to the speaker's frame, thereby moving the cone of the speaker. By applying an audio waveform to the voice coil, the cone will reproduce the sound pressure waves, corresponding to the original voice, music, etc.

Because the moving parts of the speaker must be of low mass (to accurately reproduce high-frequency sounds), voice coils are usually made with the lightest-weight wire possible. Because of this, applying too much power can cause a voice coil to overheat. Voice coils wound with flat wire (so-called flat-wound voice coils) are better able to dissipate heat than coils made of round wire. Modern coils may also use a ferrofluid in the gap between the coil and the magnet frame to assist in cooling under high power conditions; the ferrofluid conducts heat away from the voice coil to parts of the speaker that have both more thermal mass and are better-able to dissipate the heat.

Applying too much power can also cause the voice coil to bottom out against the magnet frame, causing a thumping noise and distortion. In extreme cases the cone has been known to tear off the cone.

Other uses for the term

Nowadays the term has been generalized and refers to any coiled wire that is used 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 disk heads in a moving-head disk drive. In this application, a very light weight coil of wires is mounted within a very strong magnetic field produced by rare earth permanent magnets. By means of a servo system driving the voice coil, the heads of the disk drive can be positioned very quickly and accurately.