Acoustic Guitar Pickup Primer: Part 4 Piezo, Piezoelectric Pickups
Piezo or Piezoelectric Pickups
Perhaps the piezo pickup is the hands down favorite for acoustic guitar, for it comes closest (in the opinion of many) to replicating the acoustic guitar’s sound (closer than most magnetic pickups) without many of the hassles of a microphone and being nearly invisible when installed on a guitar.
Piezo pickups sense vibration. But it only senses the vibration of the surface it is attached to such as the soundboard of the guitar, as opposed to a microphone which senses the vibration in the air which is the culmination of the entire guitar (and anything that is causing vibration in the near vicinity, such as the drums, bass, etc.). So when recording in a live environment the piezo would be the idea choice for it wouldn’t pickup other instruments being placed in the same room.
The first generation of piezo pickups were simply attached to the top, often hidden from view by being placed inside the guitar with an output jack or the now familiar combination endpin/output jack, as to keep the appearance of the instrument stock.
Since the pickup is sensitive to changes in pressure such as vibrations, it wasn’t long before it was determined that the optimum amount of pressure (hence vibration) was at the saddle of a guitar’s bridge. Soon after that under saddle pickups were developed, with one of the most notable being the landmark design by Ovation guitars which had an individual pickup for each string!
Others followed suit. So now under saddle pickups are the most popular both as factory installed pickups and after market installations, though surface mounted pickups still are marked (and more advanced magnetic soundhole pickups).
The surface-mounted pickups are heralded by some musicians with their argument being the sound of the instrument isn’t just from the bridge, but the entire top, and the larger sampling of the top produces a truer tone. To that effect, there are some systems that have two or three elements to them.
While these pickups (both under saddle and surface-mounted) may sound more “acoustic-like” than a magnetic pickup, they do have characteristics of it’s own that color the sound. Some artists have used this sound on both live albums and studio CDs alike with various degrees of success of approximating an acoustic guitar’s sound. (Some I like, such as Neil Young’s “Live Rust” recordings, and others I don’t so much for example Dave Matthew’s “Live in New York City” or the Grateful Dead’s “Reckoning” both of which typify the “plugged in” acoustic sound.)
The popularity and ease of use of these pickups have almost defined a sound all it’s own…much in the way the a Rhoads electric piano has become an instrument all it’s own even though it’s heritage was initially that of being a portable piano.
The general consensus is that (and impedance matching is a must, but most systems are now active impedance matching systems so this is seldom an issue) these pickup sound “quacky” unless assisted by outboard gear.
These pickups are more resistant to feeding back than a microphone because it’s not sensing the vibration in the air (like a mic does), but the vibration of the guitar itself.
What generally makes a good sounding acoustic guitar is sensitivity to vibration, generally the vibration of the string. But, the guitar is also sensitive to vibration from other sources, including the monitors which are reproducing the vibration of the pickup: hence, feedback.
This phenomenon let to the creation of the solid-body acoustic guitar. While not actually neither an acoustic guitar, nor a true solid-body, they match a piezo and/or pickups system with a semi-hollow (they usually have tone chambers within them) that is more resistant to feedback but look and sound like an acoustic (well, like a plugged in acoustic).
These guitars are thinner than standard acoustics to keep the weight manageable, and may or may not have soundhole. Taylor’s T5, Tom Anderson Guitarworks’ Crowdster and Epiphone’s SST are examples of this style of guitar.
But for better or worse (better, in my opinion), there were those that sought to continue the pursuit of a more true, accurate reproduction (rather than approximation) of acoustic sound leading to some of the advances to be covered later in this series, but these include feedback suppressors, active and passive d.i. boxes depending on the pickup system being used, mixing/matching of two or more pickup systems, development in new materials, old school tube technology, digital processing and an open mindset.