A guitar pickup, also known as a transducer, is an electromagnetic device that gives electric guitars their distinctive sound. Working on the principle of magnetic induction, it creates a magnetic field around itself, "pick ups" vibrations of the steel or nickel guitar strings as they interrupt the magnetic field, and converts them to an electrical signal. This signal is then relayed to a guitar amplifier and converted into an audible sound. Guitar pickups are also employed in acoustic guitars to produce louder volumes than possible with naturally produced sound-box amplification.
The structure of a pickup is simple. It consists of a thin rectangular magnet wrapped in a bobbin made of several thousand turns of very fine copper electrical wire. There can be a single coil-wrapped magnet reaching across all of a guitar's six strings or a separate one for each string. These magnets are attached with screws to the guitar body, under the strings, with the magnetized surface in the upward direction.
A guitar can have a single pickup or multiple pickups located at different positions at the neck, the bridge or pick-guard. Position is crucial since the sound of string changes along the string length; a bridge position, for example, produces a clear bright sound, while a neck position produces a softer sound. Each pickup can have a distinctive sound, which can be altered by adjusting the height of the pickup in relation to the string. Different pickup configurations or combinations produce a layered sound. Sound variations also depend on variations in magnet type, magnet strength, wire size and number of turns of the coil.
Many varieties of guitar pickups are available in the market. Magnetic pickups, which a majority of electric guitars use, come in two main styles: single coil, which has a single coil magnet for each string, and a double coil or Humbucker, which has two coiled magnets in opposite polarity. Stratocaster guitars from 1954-1979 had single coil guitar pickups. Humbuckers were developed in 1955 by Seth Lover, an engineer at Gibson, in order to cancel out the unwanted "hum" sounds from any nearby electrical wires, lighting or appliances that the single coils tend to pick up in addition to the string vibrations. Many latter-day guitars include both single coil and Humbuckers.
Optical pickups work by sensing the interruption of a light beam by the string. Ron Hoag, the inventor of this pickup, first displayed an optical pickup guitar at the music products trade exhibition NAMM Show in Chicago in 1969. Piezo electro-acoustic pickups, which use crystals to detect pressure changes, can be found in Parker Fly guitars and Godin guitars.
The difference in guitar pickups is of type and quality. Musicians generally use the ones most suited to their particular musical sound, or combine different ones to get the sound they want.