How to connect piezo speakers to an amplifier

[ChrisO]

Hello
I would like to connect a piezo speaker or better few piezo speakers to a "ordinary" amplifier to play some high frequency sine wave sounds, nothing more. Loudness is important, HiFi not, should be used as part of an alarming system. I know about sirens, they are not an option.
I also know the difference, from electronic point of view, between piezo and
inductive speakers, just don't know how to make them look the same to the amplifier.
I've spent hours searching but didn't find anything pushing me to power on my soldering iron
The speaker is: https://www.kemo-electronic.de/en/Car/Speaker/L010-Piezo-Loudspeaker.php

Would be very thankfull for any ideas.
Chris

 

[Audioguru]

ANY audio amplifier can drive the piezo speaker since its current is very low. It operates with voltage, up to 30V peak-to-peak which would be from an amplifier rated to produce 14W into 8 ohms. Its rated 15V p-p will be produced by an amplifier rated to produce 3.5W into 8 ohms.

The graph shows that it is very loud when up close and only when it produces very high frequencies that many people cannot hear. It does not show the drop in loudness at audible frequencies. Of course its loudness is reduced at a distance.

More than one high frequency speaker does not work well because the wavelength of high frequencies is small. Then if you move a little to the side then the sound level will be cancelled or doubled. Also, an amplifier might become instable due to the high capacitance of a piezo.

 

[Audioguru]

If the amplifier is an antique and uses vacuum tubes and has an output transformer then the output transformer must have its rated load.

 

[bertus]

Hello,

What are you trying to do?
The speaker is only for VERY high tones.
The linked page only has a graph from 15 to 39 kHz.
This is well above the tones human can hear.
The page shows a frequency range from 2 to 60 kHz.
I would not expect a high level at 2 kHz, due to the small size.

Bertus

 

[WHONOES]

What sort of frequency are you hoping to use?

 

[Audioguru]

My dog can hear some of those frequencies.

 

[ChrisO]

Thank you Audioguru. I was a bit unsure because I read in some places there should be an inductor in parallel with a piezo speaker.

As for what I'm trying to achieve, well, I feel a shit storm comming ;-)
I'm trying to build a "Pest Chaser" aka "Mosquito" to keep away "kids" from our stairwell.
Before somebody complains: there is no pets living in our house.

For this I would like to play some annoing 17-18 kHz sinus and see how it works.

 

[WHONOES]

Kids might hear that range but I doubt if adults would. The most annoying range is 2 to 3 Khz.

 

[Martaine2005]

Kids might hear that range but I doubt if adults would.

That's the point of using a 'mosqito'.
To annoy loitering youngsters while leaving adults alone. Some shopping malls have used this method.
It is normally about 15kHz.
Incidentally, I drive my teenagers nuts while charging Dewalt batteries. I can't hear it at all.
Edit....I have a 'Function generator' app on my phone, the tone generator is great for this purpose...
Here it is
Martin

 

[ChrisO]

@martine2005: I am in the 8-9kHz max group, so I could enjoy the silence watching the video from your link ;-)
As for tone generation no problem, there are, for Linux users likie me, sox, ffmpeg and possibly others.

My problem is, how to generate "enough" loudness, just in case it matters ;-)
The kemo piezo speaker I mentioned in my original post is the loudest I could find.
If anyone know of a louder one please let me know.
I wonder how many of them I could drive from one amplifier and how the emitted dB's "sum up".
I guess: 2 x 115 dB/W/m != 230 dB/W/m
It's quite a new area for me, so please forgive my inexperience.
Chris

 

[Audioguru]

I read in some places there should be an inductor in parallel with a piezo speaker.

That would tune the inductor and capacitance of the piezo to produce a higher level if it is fed from a fairly high impedance. But an audio amplifier has a very low impedance so it will not work. Besides the capacitance of the piezo is not accurate so you would need an adjustable inductor to set the loudest frequency.

I'm trying to build a "Pest Chaser" aka "Mosquito" to keep away "kids" from our stairwell.
Before somebody complains: there is no pets living in our house.

Teens who deafened themselves with earphones blasting acid rock will not hear high frequencies but many normal young adults will hear your high frequency and be offended.

I am in the 8-9kHz max group, so I could enjoy the silence.

No, you will hear it because your high frequency sensitivity is reduced with a slope, it is not a very steep cliff.

The kemo piezo speaker I mentioned in my original post is the loudest I could find.
If anyone know of a louder one please let me know.

Some bands use a loud awful-sounding piezo horn tweeter.

I wonder how many of them I could drive from one amplifier and how the emitted dB's "sum up".
I guess: 2 x 115 dB/W/m != 230 dB/W/m

Nope. With two tweeters you add only 3dB. With 4 tweeters you add 6dB. .But the wavelength is short so you will have phase cancellations.
The Kemo tweeter is not rated properly. 120dB at what distance and with how much power? ae 10cm or at 1m? At 1W or at its max of "14W"?

Here is a graph showing typical hearing loss with aging. Here is a sales sheet for a loud piezo tweeter.

 

[WHONOES]

I'm 71 and my ears are still OK to 11.5KHz. I have just tested them.

 

[Audioguru]

Whonoes, was your hearing professionally tested? I have normal-for-my-age high frequency hearing loss but I hear high frequencies fine when they are loud enough. My hearing aids do it.

A hearing test done by an Audiologist measures the threshold of hearing at various frequencies. Many old people (like me) have tinnitus which is a background noise. My tinnitus is very high frequencies all the time which covers up my threshold of hearing the high frequency test tones so they warble the tones for me which gets confusing about if it is the tinnitus or is the warble tones.

I have had 4 hearing tests by different Audiologists and the results are all the same. I even got paid for having one test and survey done at the University.

 

[ChrisO]

@Audioguru: thank you very much for all your explanations.
BTW, I'm 64 and for me at about 10.5kHz is the end. Just tried it. Not a proffessional test but I used very good headphones.
And don't feel like missing anything, as long as my hearing is OK in the "normal" range, it's OK.
Any more ideas for "Pest Chaser"? ;-)

 

[bertus]

Hello,

Did you see the adjustable module at the site you linked:
https://www.kemo-electronic.de/en/Animal-Repeller/Car/Modules/M094N-Marten-repeller.php

Bertus

 

[WHONOES]

No. I did it myself using a sig gen and a tweeter. I too have tinnitus which is a bit more broadband than just hiss.

 

[ChrisO]

Yes, I've just received it and two of four of them: https://www.kemo-electronic.de/en/Car/Speaker/P5123-Mini-piezoelectric-tweeter-for-M094N.php.
Somehow I got the impression, that the "Marten repeller" powered at 12V doesn't squeeze all from those tweeters, the same for the L010 tweeter.
I also received this one: https://www.kemo-electronic.de/en/Car/Speaker/L001-Piezo-spherical-dome-tweeter-with-flare.php
I guess it's time to do some experimenting with them and an amplifier...
BTW, the ksn1001A Audioguru suggested looks interesting, hard to get it in my area, CH, though.
One more question: polarity, some of tweeters I have indicate where + and - go, other not.

 

[bertus]

Hello,

Have a look at this:
http://www.simonsdialogs.com/2015/12/ultrasonic-pest-chaser-final-design/

Bertus

 

[WHONOES]

Yes, I've just received it and two of four of them: https://www.kemo-electronic.de/en/Car/Speaker/P5123-Mini-piezoelectric-tweeter-for-M094N.php.
Somehow I got the impression, that the "Marten repeller" powered at 12V doesn't squeeze all from those tweeters, the same for the L010 tweeter.
I also received this one: https://www.kemo-electronic.de/en/Car/Speaker/L001-Piezo-spherical-dome-tweeter-with-flare.php
I guess it's time to do some experimenting with them and an amplifier...
BTW, the ksn1001A Audioguru suggested looks interesting, hard to get it in my area, CH, though.
One more question: polarity, some of tweeters I have indicate where + and - go, other not.

The polarity doesn't matter unless you are going to connect 2 in parallel.

 

[ChrisO]

Bertus, I was there already. The schematic of the circuit is a bit unclear for me. Maybe I should try to ask him few questions.