Piezo transducer pickups range from under $1 all the way up to $150+.
Putting build quality, accessories like jacks and integrated preamp and volume control, is there a fundamental difference between the various options?
Specifically, I'm wondering if all piezo transducers are basically the same when you dig into them. My understanding is that they are a crystal that sends a small electric signal when vibrated. So, is there a fundamental difference between the crystal in a $100 piezo and a $5 piezo, aside from value-added accessories and packaging? Do the expensive ones have a higher quality crystal? Do different piezos give different frequency response ranges? Or is the added cost related to build quality and nothing else.
I've used a $1 piezo, and it worked alright but needed a lot of EQ and had uneven frequency responses. If I spent $100 on a piezo, will I get better frequency response, or just better soldering and wires, etc. Electronic noise is also a factor, but I didn't have buzz/static issues with the $1 option so i figure that's mostly all the same.
I do not want to have a discussion about microphone vs magnetic vs piezo. This topic is meant to be exclusively about the variance between different piezo options.
Many materials are piezo electric, but it's hard to imagine that the audio applications use anything but the cheapest and most available, and I don't think it would make any difference anyway.
But the whole mounting system is a mechanical filter/multichannel equalizer system. The vibrations you want to "transduce" into an electric signal have to get through some stuff. The piezo is also mounted on something; your $1 ones are on a brass disk. They all make a voltage when the molecules or crystal get squeezed or distorted. If it's a surface mount (on a vibrating surface), the squeezing takes place because of the inertia of the piezo and whatever it's mounted on or in. So yes, different designs do sound different. But better is in the ears of the listener.
On cigar box guitars, the $1 ones are popular. Besides the issue of where to attach the thing, folks vary how much silicone or hot-gun glue is on each side of the disk.
Look at the various options available from a specific manufacturer such as K&K. The output signal from any given mounted transducer will vary wildly by the exact size of the transducer active area. You can check this yourself by simply using sharp scissors to cut away half of your $1 transducer, keeping the wired portion, of course!
Again, download an installation pdf from K&K and read about the importance of how the transducer is mounted. Dieter from K&K is pretty transparent about the amount of time and experimental design that went into developing his product line. Any mounting that is elastomeric in nature will effect the produced sound drastically
Physical construction matters.
I can tell you first-hand that shielding the active side of a brass-backed piezo transducer will make a huge difference when it comes to how susceptible to induced AC hum the transducer assembly will pick up from its surroundings.
The main determinant factors in what is produced by a piezo transducer is first, the actual mounting, and second, the impedance of the load which it feeds.
This is all very helpful you guys, thanks for the quick education. It sounds like design/construction is a big part of sound quality. I don't understand electronics much at all, but this is enough to encourage more experimentation with the piezo options out there.