Piezo speaker limitations

[Tim Link]

I've been pondering piezo speakers, and wondering what their main limitations are. How good could one be made if a lot of effort was put in to it? Why do those piezo transducers always have to be disc shaped? I see there are piezo strip actuators. Could a piezo speaker be a thin strip, like a ribbon rather than one of those discs? Those discs have to bow in to a cup shape to make sound. Seems like the metal sheet on the back would resist that a lot. A thin strip might bend easier along it's length, allowing it to more easily reach lower frequencies and greater excursion. Also they could be used in line arrays with much closer center to center spacing than can be had with a disc shape.

 

[solderdude]

Biggest problem is maximum excursion making them really only suited for use as tweeter or as a headphone driver (with limited bass response).
They are limited in max. input voltage and when wanting them to cross-over at a different frequency than their natural roll-off you need to add a resistor in parallel to it as they are a capacitive load meaning the impedance drops the higher the frequency is.

 

[Tim Link]

Biggest problem is maximum excursion

I've seen that piezo strips have much better excursion than the discs. They can be used to move flaps on radio control airplanes, or even as flapper fans to cool electronics.

 

[kemmler3D]

I've seen that piezo strips have much better excursion than the discs. They can be used to move flaps on radio control airplanes, or even as flapper fans to cool electronics.

Are the actuators themselves moving far, or are they using some kind of mechanical linkage or gear to produce larger motions?

I guess a more direct question is - what's the largest linear motion a piezo strip can make?

You can then figure out its capabilities as a speaker using a calculator like this (after converting the strip area to the equivalent diameter of a circle): https://www.baudline.com/erik/bass/xmaxer.html

 

[solderdude]

These will have very high capacitance >100nF or even > 1uF which audio amplifiers won't like directly in parallel with their output.
One could add a small series resistance but that will roll-off treble. These too are limited in frequency range.
Fine as actuators (with very small excursions).

 

[kemmler3D]

These will have very high capacitance >100nF or even > 1uF which audio amplifiers won't like directly in parallel with their output.
One could add a small series resistance but that will roll-off treble. These too are limited in frequency range.
Fine as actuators (with very small excursions).

Solvable in an active speaker with compensating EQ though, maybe?

 

[solderdude]

Not enough for decent bass response levels. They would have to become really big for low bass resulting in many uF connected directly to the output of an amp causing most amps to become unstable.

Bigger panels like the Sonitron SPS-68-T00 can reach 250Hz but require a high voltage and won't do low bass and are 1.1uF and limited to 21V (100W/4ohm).

You would need a bunch of them to get good SPL and would still need a SW XO'ed at 250Hz.

 

[kemmler3D]

Not enough for decent bass response levels. They would have to become really big for low bass resulting in many uF connected directly to the output of an amp causing most amps to become unstable.

Would using a current-drive amp help at all?

I wonder if you could do an MBL-style cylindrical piezo speaker, like 1m+ tall, and then use a normal woofer for actual low bass. As I am describing this, it sounds expensive, though.

 

[solderdude]

current drive would modify the FR so one would have to compensate for that.

Dragonfly™ - World's first full range piezo speaker

Cutting-edge piezo speaker specially designed to deliver a full range frequency response. An ideal choice for a wide range of audio projects.

flora.tech

https://flora.tech/wp-content/uploads/2023/11/Dragonfly-data-sheet_rev5_11162023.pdf

works like exciters.

 

[Tim Link]

current drive would modify the FR so one would have to compensate for that.

Dragonfly™ - World's first full range piezo speaker

Cutting-edge piezo speaker specially designed to deliver a full range frequency response. An ideal choice for a wide range of audio projects.

flora.tech

https://flora.tech/wp-content/uploads/2023/11/Dragonfly-data-sheet_rev5_11162023.pdf

works like exciters.

That's an interesting product! An exciter that's only 3mm thick.

 

[kemmler3D]

current drive would modify the FR so one would have to compensate for that.

Dragonfly™ - World's first full range piezo speaker

Cutting-edge piezo speaker specially designed to deliver a full range frequency response. An ideal choice for a wide range of audio projects.

flora.tech

https://flora.tech/wp-content/uploads/2023/11/Dragonfly-data-sheet_rev5_11162023.pdf

works like exciters.

Very interesting, but also requires up to 80V (!) and distortion is not mentioned anywhere, not even once, which makes me suspect it's terrible. I think it is also not "like" an exciter, but it is one, in the FAQs the mention it doesn't produce much sound on its own.

 

[Tim Link]

Very interesting, but also requires up to 80V (!)

I've got an AC/DC album I could try on that.