Acoustic Power: The magic of piezoelectricity
Piezoelectric materials are a bit magic.
Certain solid materials can ‘generate’ an electrical charge when they’re squished or streteched. Magic. Sort of.
An electric generator works by moving a coil of wire in a magnetic field. Electricity happens if you do this. An electric guitar or bass pickup works by vibrating a string in the pickup’s magnetic field. Electricity happens if you do this and its ’signal’ reflects the vibration of the string.
An undersaddle piezo pickup works by being ‘deformed’ (alternately squashed and stretched microscopically) by string vibrations passed through the saddle. Like a regular magnetic pickup, the electricity that’s generated follows the sting vibration.
As Arthur C. Clarke said, "Piezoelectric technology is indistinguishable from magic." Probably.
All magic.
This ability of piezoelectric materials to be used to amplify instruments has been known for some time. Things really kicked off in the ‘70s though, when Ovation and Takamine began fitting (quite different) piezo pickups into their guitars.
Suddenly, using an acoustic guitar on stage became a much more practical matter. Piezo was here to stay and soon, pretty much every acoustic builder was offering some sort of pickup option.
I want to take a look at a couple of quirks of different acoustic guitar pickups over the next while so it’ll definitely be useful if I go into a little detail about how these things actually work.
Piezo Undersaddle Pickups: How They Work
The basic concept of a piezo pickup is to have a positive and negative conductor with a hunk of magic piezoelectric material sandwiched between them.
This assembly sits under your guitar saddle (hence the ‘undersaddle’ thing), and the strings sit on the saddle.
String vibrations are transferred, through the saddle, to the pickup. This vibration will cause tiny fluctuations in compression and the piezo material turns these fluctuations into an electrical signal. That signal can then be sent off to a PA so the entire stadium can hear you play Every Rose Has Its Thorn.
While there are many variations, the exploded image below shows a very simplified version of these pickups.
Like I say, it’s pretty simplified but it does the trick. The copper strip is the ‘positive’ conductor and the housing channel forms the negative conductor. There’s a separate piezo element for each string (although the signals from each all run ‘together’ — there’s only one signal path to the amp).
Put ‘em under pressure
The hugely important thing to remember about piezo undersaddle pickups is that they won’t function well without effective transfer of those string vibrations. Again, more details in the future but, for now, I’ll point you at an article where I discuss one of the most important aspects — string break angle.
Terminology: Transducer
You might have seen undersaddle pickups called Undersaddle Transducers (abbreviated to UST).
A transducer is any device that converts one form of energy into another.
So, for instance, a magnetic pickup in an electric guitar converts vibrating string energy into electricity. It’s a transducer. Likewise, a piezo pickup also converts vibrating string energy into electricity (the only difference is how that string energy gets transduced).
Which brings me to…
Piezo soundboard transducers
We know about undersaddle transducers (pickups) so let’s take a whistle-stop tour of the other application of piezo technology that’s relevant to the musician: soundboard transducers.
The principal is mostly the same as with other pickups — turn vibrations into electricity. Instead of getting those vibrations transferred through the saddle material, this pickup is fixed or adhered to the guitar soundboard/top. It’s sensing the vibrating top.
The construction of these is pretty simple. A thin piezoelectric element is glued to a thin metal (usually brass or similar) disc. The vibrations from the guitar top are transferred to the piezo element and turned into lovely electricity
IMG
The big question: How to pronounce ‘piezo’
I’ve heard (and used) a number of different pronunciations over the years. However, Merriam-Webster recommends the following (and most people seem to have settled there):
pē-ā-zō
That’s nice long vowel sounds all ‘round.
ē as in evil
ā as in ace
ō as in go
pē-ā-zō, got it?
Right. That’s the basics of how piezo pickups work and the important bit about how you say it. I’ll get into some more detail later — properties of different types, problems, installation, etc. For now, digest and practice… pē-ā-zō… pē-ā-zō… pē-ā-zō. 😉
This article written by Gerry Hayes and first published at hazeguitars.com
