How Do Pick-Ups on an Electric Guitar Work?
Although they might have distinct shapes and colors, every electric guitar uses a pick-up. A string vibrates to cause an electrical current from the pick-up to run to an amplifier, then to a speaker and then to your ears. A few variations of guitar pick-ups can transfer the physical vibrations of a string to an electrical signal, but guitar makers (luthiers) most commonly use electromagnetic pick-ups.
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History
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In 1931, George Beauchamp of Rickenbacker International Corporation (formerly Ro-Pat-In Corporation and Electro String Instrument Corporation) built the first guitar using an electromagnetic guitar pick-up. He used two horseshoe magnets wrapped around the strings and a coil of wire underneath the strings. The overall shape of the instrument led enthusiasts to nickname the guitar "Frying Pan." Although filed in 1932, the patent office did not reward a patent for the magnetic pick-up technology until 1937, giving other manufacturers time to create their own electric guitars using this model.
Permanent Magnet
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A permanent magnet creates a static magnetic field through the air--the closer to the magnet, the stronger the strength. Pick-ups can use long bar magnets or individual button-style magnets to create the field. The size and material of the magnet affect the field strength. Rare earth magnets have greater strength than AlNiCo magnets. AlNiCo magnets have greater strength than ceramic magnets. You will not, however, always desire a stronger magnet. Although a stronger magnet can induce a stronger electrical current, it might also grab the string too tightly so that the string cannot freely move when struck.
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Ferromagnetic Strings
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Given an external magnetic field, a ferromagnetic material lines up its electron spins parallel to the field. The permanent magnet in the pick-up lines up the ferromagnetic string's electron spins. When struck, the string vibrates at a certain frequency, and its physical movement oscillates the magnetic field around it.
Coil of Wire
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A coil of wire with an electric current running through it creates a magnetic field. On the other hand, an oscillating magnetic field induces an oscillating electric current through a coil of wire. Guitar pick-ups use a coil of wire to "pick up" the ferromagnetic string's magnetic vibrations and transfer them into an electrical signal. This signal then runs out of the guitar to an amplifier and a speaker.
Piezoelectric Pick-Ups
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Some electric guitars, as well as acoustic guitars, use piezoelectric pick-ups on the bridge to convert the physical motion of a string to an electrical signal. A mechanical strain on the piezoelectric crystals causes the crystals to electrically polarize. An oscillating motion induces an alternating electrical current from the pick-up to an amplifier and speaker. When used on an electric guitar, a piezoelectric pick-up emulates an acoustic guitar tone.
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References
- Photo Credit Tonabnehmer image by Jakob Sons from Fotolia.com
