By Tom Mulhern
Along the same lines of "You say ‘to-MAY-to’ and I say ‘to-MAH-to’ is the ever-present confusion over pronouncing the word "piezo." Almost every guitarist knows it’s a type of pickup, but you’re unlikely to hear any two pickers articulate it the same way. Some say "PIE-zo," while others say "PEE-zo," "pee-AY-zo," etc. According to Webster’s Encyclopedic Unabridged Dictionary, it’s pronounced "pie-EE-zo." Regardless of how anyone utters its name, piezo means pressure, and piezoelectricity is a phenomenon in which electricity is produced by placing mechanical pressure on nonconducting crystal. Because it changes one form of energy (pressure) into another (electricity), anything using the piezo principle is known as a transducer. To be fully accurate, microphones, magnetic pickups, and even speakers are transducers (yep, transduction works in reverse, too). In the 1970s, when piezo pickups were first introduced to acoustic guitars, they were almost universally called transducers to avoid a mixup with magnetic pickups. Unfortunately, confusion wasn’t averted, because some called them "transducer pickups."
Piezo pickups of one kind or another have been used since before World War II, most often in inexpensive microphones. Piezo pickups once replaced magnetic pickups–in phonographs. During the 1930s, when electrical recording was still in its infancy, a way was found to grow crystals that could be used in the pickup attached to a needle that played records. The result was less weight (and hence, less wear on the records’ grooves), greater fidelity, and lower cost than magnetic pickups could offer. (Les Paul often relates that in 1929 he took the tone arm off of his dad’s phonograph, stuck the needle into his guitar, and used the rest of the phono as an amp; his setup obviously used a magnetic phono pickup, but the principle would work the same way with a piezo setup.) Because of their extreme sensitivity and extraordinarily wide frequency-response range (typically from less than one cycle per second all the way up to hundreds of thousands of cycles per second), piezo transducers and piezo film are used in all sorts of gadgets, from scales to blood-pressure monitoring gear, to earthquake sensors.
Because their frequency-response range is huge–going from well below human hearing to many times above it–most people perceive piezo transducers to sound too bright. In actuality, magnetic pickups sound dull, because their range is only several thousand Hertz (cycles per second). As a result, this added brightness gives an acoustic a sound more like a guitar miked by a condenser microphone. An added advantage is that piezo transducers work by sensing changes in pressure (vibrating strings on the bridge saddle, for instance), so nylon strings and bass strings work as well as steel strings–with different resulting volume levels, of course.
Today, piezo pickups come in stick-on types and under-saddle types. The stick-on types are convenient, but require careful placement so that they pick up the best sound from a guitar. Under-saddle piezos are usually a single strip that fits into a slot routed beneath the saddle. Recently, piezo transducer elements have been implanted into the saddles of electric guitar bridges, creating a new type of hybrid. As the technology of piezo transducers for guitars has matured, so has the technology of getting better tone. Initially, piezo transducers sounded brittle, edgy, overly bright. A large part of that was due to a huge impedance mismatch between the transducer and the amp or other gear it was plugged into. Today, most transducers come with a preamp/tone module that lets you tailor the highs while matching the impedance to the downline equipment.