Connecting multiple piezo ceramic elements in a sound installation

[terjeabusdal]

Hi there,

I am a Norwegian artist working on a project with field recordings, and I was wondering if I may ask here some questions with regards to use of piezo ceramic elements as speakers. I plan to make an sound installation of at least 100 of them mounted to a wall, which will all play the same recording.

In the past days I have been trying to google my way to how to do this. The internet is full of conflicting advice (or probably I am not asking the right questions) – in any case, I am completely lost.

So, to be very concrete, this is what I currently have:

• 100 piezo ceramic elements in size 27 mm + 100 piezo in size 35 mm
• 1200 watts amplifier from Thomann
• Omnitronic ELA-T30 Transformer 30 W

Could anyone point me in the right direction of how to proceed from here? Here are some basic questions I was wondering as a start:
- Should I connect the piezo in parallell or series?
- Will I need to use resistors somewhere? (I read one place that this was needed, but did not really understand why).
- Should I run the signals from the amplifier through the transformer?

I attach a picture of the transformer in question, as well as a picture of a similar installation with piezo so you can see what I am trying to achieve. Below are also the stats from the supplier of the piezo ceramic elements that I have bought.

Diameter // Resonant Frequency // Resonant Impedance // Capacitance
27mm 4.0KHz ±0.3KHz 200W 25,000pF ±30%
35mm 2.6KHz ±0.3KHz 200W 24,000pF ±30%

Any help is greatly appreciated! I understand that on this forum, these are probably quite basic questions so please bear with my ignorance.

Best regards,
Terje

 

[Audioguru]

What kind of sounds will your many piezos play?

The cheap piezo elements are designed to be the single sound frequency beeper in a smoke alarm. They are not to be fed from an audio amplifier because they are useless for music and will cause a voice to be very tiny and beepy.
None of the Chinese sellers provide any sound specs for those piezos.

The transformer is made to drive one normal low impedance coil and magnet speaker from a 100V output on a PA amplifier and not for those piezos.

 

[terjeabusdal]

Hi, thank you for your answer.

The sounds played are some old wax roll recording of voices from the early 1900s, along with sounds from nature. I understand this setup will not sound like a proper speaker at all, and I am interested in using these piezos primarily because of the visual qualities when grouped on a wall.

Now I did already try to connect ten of them in parallell and it seemed to work ok. It does sound tiny and beepy as you point out, but in this case and for this use, it is ok. When I ran the signal from the amp through the transformer (in reverse), it became stronger/louder.

Perhaps I could ask you, if I use this setup with 100 in parallell, am I at risk of destroying the amp (or anything else)? I have seen that when hooked up to an Arduino, they connect a resistor in series with the piezo.

PS. I bought the piezos from a supplier in the UK and he provided sound specs I posted earlier. Pretty sure he got them from China though.

 

[bertus]

Hello,

The piezo speakers can have very narrow frequency range.
Only the frequencies given (27mm 4.0KHz ±0.3KHz and 35mm 2.6KHz ±0.3KHz) will be reproduced.
If you seller can give you a spectrum like in the link, you can tell more about the reproduction of the sound:
https://itectec.com/electrical/elec...piezo-elements-and-generating-multiple-tones/
As you can see the spectra are quite different.
The second graph only shows responce at high frequencies.

Bertus

 

[Audioguru]

Perhaps I could ask you, if I use this setup with 100 in parallell, am I at risk of destroying the amp (or anything else)? I have seen that when hooked up to an Arduino, they connect a resistor in series with the piezo.

The specs for the piezos shows that they have a high capacitance that cuts high frequencies when fed from a series resistor and the capacitance is multiplied by your quantity of 100 for one piezo and another 100 for the other piezo.. An audio amplifier can be destroyed when driving such a high capacitance.

PS. I bought the piezos from a supplier in the UK and he provided sound specs I posted earlier. Pretty sure he got them from China though.

I saw NO sound specs. The very basic sound spec is the sound pressure level at a certain frequency with a certain input level which was not listed. I do not know why "200W" was listed.
I am glad that you understand that the piezo speaker is a shrieker or squeaker instead.

 

[terjeabusdal]

The specs for the piezos shows that they have a high capacitance that cuts high frequencies when fed from a series resistor and the capacitance is multiplied by your quantity of 100 for one piezo and another 100 for the other piezo.. An audio amplifier can be destroyed when driving such a high capacitance.

Thanks for the answer. Is there a safe way to drive these without running a risk of destroying the amp? I have seen it been done earlier, but I am not sure how they did it behind the scenes. I am taking my assumptions from this video:

 

[terjeabusdal]

Hello,

The piezo speakers can have very narrow frequency range.
Only the frequencies given (27mm 4.0KHz ±0.3KHz and 35mm 2.6KHz ±0.3KHz) will be reproduced.
If you seller can give you a spectrum like in the link, you can tell more about the reproduction of the sound:
https://itectec.com/electrical/elec...piezo-elements-and-generating-multiple-tones/
As you can see the spectra are quite different.
The second graph only shows responce at high frequencies.

Bertus

Hi, thank you for the link! I understand the sound quality will be poor, but for now I am trying to understand how to safely configure the setup.

 

[Audioguru]

Why play the sounds of insects and ticking? I also heard a few short duration high frequency beeps in the video.
Try any amplifier and if it blows up then try another then another until you find an amplifier that survives.

 

[terjeabusdal]

Why play the sounds of insects and ticking? I also heard a few short duration high frequency beeps in the video.
Try any amplifier and if it blows up then try another then another until you find an amplifier that survives.

So to sum up: it does not matter if I attach resistors anywhere in this setup?

 

[Audioguru]

A resistor parallel with each piezo simply loads down the amplifier more causing the amplifier to be overloaded.
A resistor in series with each piezo reduces the effect of its high capacitance overloading the amplifier but causes high audio frequencies to be reduced so there is almost no sound.

 

[terjeabusdal]

Ok, thank you for your help.