Hi All
I wanted to enquire whether a speaker needs to be driven via a bipolar sinusoidal waveform or can it be driven by a bipolar square wave, for the piezoelectric part to move mechanically I am less concerned about the actual sound quality but more about the piezoelectric part moving just wanted to enquire about this.

Kind Regards

Art

 

A square wave will be fine.

 

There are three states a piezo can be in: In its natural state the piezo is in a neutral position, neither distorted positively or negatively. The other two states are positive distortion or negative distortion. Why is this important? Because if you pulse a piezo with a positive signal, be it square wave or sinusoidal or even audio, once it's distorted in one direction it won't come back to neutral unless the charge across it is dissipated. Using a single sided square wave will produce 50% of the total movement of the crystal. So if when you drive the piezo with a positive pulse then short its plates during the zero voltage phase of your square wave you should get some decent sound out of it. But if you can power it positive for the positive square waveform then negative during the neutral part of the square waveform then you'll get more volume out of it.

Take a 9 volt battery and touch its leads to the terminals. Then disconnect it. Then touch it in the same exact way again. You'll hardly notice any response the second time. But if you disconnect it from the battery then short its terminals you'll notice some sound. Then when you touch it again you'll get the same initial sound every time. NOW, touch it to the battery one way, then touch it the other way around, switching polarity you'll get a much more noticeable response.

Yes, you can drive it with a square wave, but unless you also discharge it you won't get much response out of it at all.

 

There are three states a piezo can be in: In its natural state the piezo is in a neutral position, neither distorted positively or negatively. The other two states are positive distortion or negative distortion. Why is this important? Because if you pulse a piezo with a positive signal, be it square wave or sinusoidal or even audio, once it's distorted in one direction it won't come back to neutral unless the charge across it is dissipated. Using a single sided square wave will produce 50% of the total movement of the crystal. So if when you drive the piezo with a positive pulse then short its plates during the zero voltage phase of your square wave you should get some decent sound out of it. But if you can power it positive for the positive square waveform then negative during the neutral part of the square waveform then you'll get more volume out of it.

Take a 9 volt battery and touch its leads to the terminals. Then disconnect it. Then touch it in the same exact way again. You'll hardly notice any response the second time. But if you disconnect it from the battery then short its terminals you'll notice some sound. Then when you touch it again you'll get the same initial sound every time. NOW, touch it to the battery one way, then touch it the other way around, switching polarity you'll get a much more noticeable response.

Yes, you can drive it with a square wave, but unless you also discharge it you won't get much response out of it at all.

Sorry just to clarify say if I drove the piezo with the a square wave from a class d amplifier without the LC filter going from a positive to negative voltage, the piezo part should still mechanically move in a similar fashion?

 

To clarify - yes.

 

To clarify - yes.

great thank you so much appreciate the assistance

 

A square wave will be fine.

thank you for the assistance