Humbuckers

A humbucking pickup, humbucker, or double coil, is a type of electric guitar pickup that uses two coils to "buck the hum" (or cancel out the interference) picked up by coil pickups. Most pickups use magnets to produce a magnetic field around the strings, and induce an electrical current in the coils as the strings vibrate (a notable exception is the piezoelectric pickup). Humbuckers work by pairing a coil with the north poles of its magnets oriented "up", (toward the strings) with a coil which has the south pole of its magnets oriented up. By connecting the coils together out of phase, the interference is significantly reduced via phase cancellation. The string signals from both coils add up instead of canceling, because the magnets are placed in opposite polarity. The coils can be connected in series or in parallel in order to achieve this hum-cancellation effect, although it's much more common for the coils of a single pickup to be connected in series. In addition to electric guitar pickups, humbucking coils are sometimes used to cancel hum in dynamic microphones.

Hum is caused by the alternating magnetic fields created by transformers and power supplies inside electrical equipment using alternating current. While playing a guitar without humbuckers, a musician would hear a hum through the pickups during quiet sections of music. Sources of studio and stage hum include high-power amps, processors, mixers, motors, power lines, and other equipment. Compared to unshielded single coil pickups, humbuckers dramatically reduce hum.

The "humbucking coil" was invented in 1934 by Electro-Voice, an American professional audio company based in South Bend, Indiana that Al Kahn and Lou Burroughs incorporated in 1930 for the purpose of manufacturing portable public address equipment, including microphones and loudspeakers.

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