Voice coil

Loudspeaker part A 7.5 cm diameter dual voice coil from a subwoofer driver A voice coil (consisting of a former, collar, and winding) is the coil of wire attached to the apex of a loudspeaker cone. It provides the motive force to the cone by the reaction of a magnetic field to the current passing through it. The term is also used for voice coil linear motors such as those used to move the heads inside hard disk drives, which produce a larger force and move a longer distance but work on the same principle. In some applications, such as the operation of servo valves, electronic focus adjustment on digital cameras, these are known as voice coil motors (VCM). Operation By driving a current through the voice coil, a magnetic field is produced. This magnetic field causes the voice coil to react to the magnetic field from a permanent 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 input signal. Design considerations Because the moving parts of the speaker must be of low mass (to accurately reproduce high-frequency sounds without bein