Piezo comes from the Greek word that means “to squeeze.” Piezo pickups are formed from a crystal or ceramic material, which produces electricity when stressed. They function by the piezo element senses the small changes in pressure as the string vibrates, and produces alternating current. An electrical charge is pumped down a wire proportional to the amount of pressure applied.
Most factory-installed piezo pickups are placed underneath or within the string bridge, where vibrations are the strongest. When under-string placement is not possible or practical (or for temporary use), piezo pickups are mounted with glue or tape to a part of an instrument that receives the most vibrations. For most stringed instruments, the ideal surface for mounting is the instrument’s soundboard or bridge. Graph Tech encapsulates our piezo elements within our ghost saddles.
Piezo pickups were developed in the late 1960s. Prior to that time, amplified acoustic musicians had to stay in one place on the stage to accommodate microphone placement. Piezos also allow musicians to alter the sound of their instruments, when used in conjunction with a tone-adjustable pre-amp or amplifier.
Piezo pickups have a very different sound from magnetic pickups, and also have the advantage of not picking up any other magnetic fields, such as mains hum and feedback from monitoring loops. In hybrid guitars, this system allows switching between magnetic pickup and piezo sounds, or simultaneously blending the output. Piezos are capacitive devices and the sound changes dramatically with the input impedance of the amplifier you use, so a pre-amp is commonly used. A preamp is a small electronic interface that buffers the pickup from these variations and ensures full-frequency response. Unlike the magnetic pickups used in electric guitars, piezos are very good at sensing higher frequency sounds, making them ideal for acoustic guitar applications, which have a higher proportion of the upper frequency sound than their electric counterparts. As they work with pressure rather than magnetism, they are also well suited to non-magnetic strings, such as bronze or even nylon.
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