The nearer to the bridge the pickup is mounted, the more the high-order harmonics are stressed.Īnother important factor is the so-called 'magnetic aperture' of the pickup: how much of the string's length interacts with the pickup's magnetic field. So that's the physics, but what gives a pickup its own sound? The positioning of the pickup is vitally important: different emphasis will be given to different harmonics depending on how far away the pickup is from the end of the string (the bridge). Other pickups may use a plastic or non-ferrous metal cover, while others simply have adhesive fabric tape wound around the coils. Some pickups have a metal cover to protect the delicate coils and to provide a measure of shielding, and these colour the sound as they interact with the magnetic field of the pickup. Modern Strat designs have a reverse-wound, reverse-magnet middle pickup, so that you can get a humbucking effect when the middle pickup is selected at the same time as the neck or bridge pickup (positions two and four). The two coils are connected out-of-phase, but inverting the magnets in one puts the signal from the vibrating strings back in phase and cancels out induced noise.
The signal picked up from the strings combines in a positive way, but any induced hum tends to cancel, much like a balanced microphone connection. A humbucker comprises a pair of single-coil pickups mounted side-by-side, with the magnetic polarity inverted in one, and the coils connected in series. The humbucking pickup, devised by Gibson engineer Seth Lover in the '50s, counters this problem. Careful screening can improve the situation, but is rarely entirely successful in today's stage environments, festooned, as they are, with computer-controlled lighting (even a local pub's light dimmer can cause problems). Although single-coil pickups can sound excellent, they tend to pick up electromagnetic interference from sources such as power transformers and lighting dimmers. Different magnet types produce a different shape of magnetic field, which will affect the sound of the pickup. The Fender Strat pickup is a typical single-coil design, with six magnetised pole-pieces (each one a short bar magnet) wrapped with a large number of turns of fine, insulated copper wire (although some budget imported Strats have a ceramic magnet stuck to their base and the pole-pieces are simply soft iron). The magnet may be made of magnetised steel or a magnetic alloy, such as Alnico (Aluminium, Nickel and Cobalt), Samarium Cobalt or Neodymium, although in some designs a ceramic magnet is used to energise soft iron pole-pieces that are placed in contact with it. Single-coil pickups are the simplest, and comprise either a single central magnet or separate magnets beneath each string.
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