Piezoelectric mics differ from their counterparts because they use a Piezoelectric crystal as a transducer.
With that out of the way, this is how a piezoelectric microphone actually works:
In a crystal microphone, a thin piece of Piezoelectric material is attached to a diaphragm, and as the diaphragm deflects the crystal, it receives opposite charges on either side.
These charges are directly influenced by the amount of deflection on the crystal, and they inherently subside as the stress is released.
While most microphones will produce a signal by detecting vibrations in the air, Piezoelectric transducers depend on contact with solid objects to produce a signal.
As a result, Piezoelectric transducers are sometimes referred to as contact microphones.
Piezoelectric Microphone Materials, Construction & Specs
Fun fact — early Piezoelectric crystal mics used salt to produce signal.
However, it was soon discovered that this made them susceptible to moisture and heat, which was not ideal.
These materials were eventually altered to incorporate ceramics such as Barium Titanite and Lead Zirconate, making the microphones more resilient.
The top end of a crystal microphone is generally limited to a frequency (pitch) of around 10khz, and the design of the Piezoelectric microphone also limits its inherent transient response.
Despite having a high output, the frequency response of the Piezoelectric microphone did not match that of professional-level Dynamic and Condensor mics at the time. As a result, they were never considered to be suitable for professional studio environments.
Where To Find Piezoelectric Microphones In Use
So if they weren’t being used in professional music studios, what were the primary applications of the piezoelectric microphones?
In their formative years, crystal microphones were commonly found used in the handsets of telephones and also incorporated into public address systems.
Ceramic piezoelectric microphones were also used heavily within the Radio and Broadcasting industry.
The Death & Resurgence of the Piezoelectric Microphone
Much like the fate they incurred upon the Carbon microphone of its day, the Piezoelectric Microphone heavily waned in popularity from the 1970s onwards.
This was due to the increasing use of Dynamic and Condenser Microphones in the industries the Piezo mic had previously dominated.
This led to a period in which many manufacturers discontinued the production of crystal mics.
However, as is common within the world of audio, a resurgence of interest in crystal sound has occurred in more recent decades.
Subsequently, many manufacturers, such as Shure began to bring some models back into production and make them widely available to the public once again.
The Piezoelectric Microphone also found new use cases in other technologies, including the Piezo bridge for electric guitar.
Piezo microphones have found an avid following among a variety of musicians, including harmonica players and acoustic guitarists, with the first use of Piezo pickups being used to amplify an instrument occurring in 1920 on piano.
Enter: The Piezo Bridge
The incorporation of piezo bridges for electric guitar gave electric guitarists the ability to incorporate more authentic acoustic sounds into their setups without the need to physically switch guitars in the process.
The benefits are unparalleled in live scenarios, where quick changeovers are an essential part of a smoothly-running show.
These piezo bridges, such as the Fishman Powerbridge differ greatly from the magnetic pickups found on all electric guitars.
Rather than depending on the string’s vibration within a magnetic field and then converting these acoustic vibrations into an electric signal, the transducers on a piezo bridge are located within the bridge saddles themselves.
These units utilize the contact between the strings and the saddles to pick up the strings’ vibration, amplifying them via a preamplifier, and producing a tone more akin to that of a traditional acoustic guitar than that of an electric one.
In truth, while most would describe the tone of a piezo bridge as being “acoustic”, it is a direct amplification of the strings, body wood, and bridge of the electric guitar itself.
It’s truly a tone unique to itself more so than being a mere emulation of the sound of an acoustic guitar.
Other Forms Of Piezo Technology
Piezoelectric MEMS is another form in which piezo technology has found its way into modern society.
Piezoelectric Microelectromechanical Systems work under the same principles we have discussed previously in this article.
However, piezoelectric MEMS do so on a microscopic scale, often utilizing microchips. Development of this technology first originated in the 1990s and has been incorporated into numerous devices including inkjet printer heads, switches, and sensors.