Guitar pickups come in many different designs and varieties, intended to produce a broad spectrum of sounds and tones for players of different genres. A jazz player would be looking for very different characteristics in a pickup than someone who played thrash metal. The output level is one of the most striking characteristics of a pickup. As well as creating more volume, high output pickups have a number of specific tonal and electronic attributes that make them different.
Guitar pickups generally have one or two coils, spools of magnetic wire that create an electromagnetic field around the pickup. The vibration of the strings disturbs this field, creating modulation of the signal. The amplifier then converts these modulations into sound. The single coil came first, and is generally a lower output pickup. Humbuckers were introduced as an upgraded version of the single coil. They feature a pair of coils, wound in opposite directions. They create a larger magnetic field, capturing more of the vibration. However, their larger size means that they aren't compatible with all guitar types.
The electromagnetic field generated by the pickups is extremely sensitive, it can be manipulated by any number of electronic devices that give off a field of their own. Televisions, fluorescent lights and speakers all give off a field that can cause buzzing or humming in the signal of a nearby guitar. High-output pickups are much more sensitive to electronic interference, due to their higher volume. However, high-output pickups are often double-coil units, and winding the coils in opposite directions has a phase-canceling effect that overrides much of the electrical interference, hence the name "Humbuckers."
After the coils are wound, pickups are often dipped in wax or a similar sealing agent, in order to make their assemblies airtight. Pockets of air, subjected to the high frequency vibrations in the body of a guitar, create a high-pitched "squealing" sound. High-output pickups suffer from this problem more frequently, as their construction has a greater number of crevices and small spaces where the wax may not penetrate. Their higher volume also makes quieter squeals more audible. On a guitar with low-output pickups, those quieter squeals might be masked by the guitar sound, or not detected at all. Higher output pickups generally amplify handling noise and other undesirable sounds much more than the low output versions.
Despite their different technical qualities, the tone of a pickup is likely to be the deciding factor for a player. Low-output pickups have a smoother, more mellow and rounded sound, ideal for players of jazz and country. High-output pickups have fat bass and piercing highs, ideal for rock and metal players who need to cut through the mix, and generally create as much volume as possible.
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