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How to connect piezo speakers to an amplifier

Discussion in 'Audio' started by ChrisO, May 6, 2020.

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  1. ChrisO

    ChrisO

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    May 6, 2020
    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
     
    Last edited by a moderator: May 6, 2020
  2. Audioguru

    Audioguru

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    Sep 24, 2016
    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.
     
  3. Audioguru

    Audioguru

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    Sep 24, 2016
    If the amplifier is an antique and uses vacuum tubes and has an output transformer then the output transformer must have its rated load.
     
  4. bertus

    bertus Moderator

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    Nov 8, 2019
    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
     
  5. WHONOES

    WHONOES

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    May 20, 2017
    What sort of frequency are you hoping to use?
     
  6. Audioguru

    Audioguru

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    Sep 24, 2016
    My dog can hear some of those frequencies.
     
  7. ChrisO

    ChrisO

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    May 6, 2020
    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.
     
  8. WHONOES

    WHONOES

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    May 20, 2017
    Kids might hear that range but I doubt if adults would. The most annoying range is 2 to 3 Khz.
     
  9. Martaine2005

    Martaine2005

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    May 12, 2015
    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
     
    Last edited: May 8, 2020
  10. ChrisO

    ChrisO

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    May 6, 2020
    @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
     
  11. Audioguru

    Audioguru

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    Sep 24, 2016
     

    Attached Files:

  12. WHONOES

    WHONOES

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    May 20, 2017
    I'm 71 and my ears are still OK to 11.5KHz. I have just tested them.
     
  13. Audioguru

    Audioguru

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    Sep 24, 2016
    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.
     
    Cannonball likes this.
  14. ChrisO

    ChrisO

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    May 6, 2020
    @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"? ;-)
     
  15. bertus

    bertus Moderator

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    Nov 8, 2019
  16. WHONOES

    WHONOES

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    May 20, 2017
    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.
     
  17. ChrisO

    ChrisO

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    May 6, 2020
    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.
     
  18. bertus

    bertus Moderator

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    Nov 8, 2019
  19. WHONOES

    WHONOES

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    May 20, 2017
    The polarity doesn't matter unless you are going to connect 2 in parallel.
     
  20. ChrisO

    ChrisO

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    May 6, 2020
    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.
     
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