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Frequency response of a piezo speaker? — Parallax Forums

Frequency response of a piezo speaker?

kf4ixmkf4ixm Posts: 529
edited 2011-09-01 18:34 in General Discussion
Hi all, im working on a project to generate a swept audio frequency from 30khz to 60khz through a piezo speaker, like the BarkOff contraptions for sale. basically, it produces a frequency between 30khz to 60khz that dogs can hear, whenever a loud sound is detected with a microphone, (like a dog's bark) that is supposed to irritate dogs to make them stop barking (supposedly). I've got the circuit and programming made in .spin, using the PropLab design platform, and verified the frequency is being generated as desired with a o'scope. the thing im not sure of it that the piezo speaker is capable of producing frequencies in that range. i've tried the circuit, using my mother's lil 'ankle-biter', missy, as my 'lab rat', but she just lay's there and looks at me, then goes back to sleep, so im not sure that the piezo speaker is actually producing the sound. i've google'd for the answer but haven't came up with any useful info. im thinking that the frequency response of any given piezo speaker will be dependent on the size of the element itself. can anyone verify this? anyone have any ideas?

Thank you for any input and/or suggestions!

Comments

  • ercoerco Posts: 20,259
    edited 2010-09-19 09:16
    I haven't gotten into ultrasonics, but piezo speakers definitely have resonant audio frequencies and are much louder at those freqs. Some dogs react more to those ultrasonic repellers, wonder if your dog can't hear, doesn't care or won't react. Maybe borrow a known working Barkoff unit and see if he reacts.
  • ElectricAyeElectricAye Posts: 4,561
    edited 2010-09-19 09:25
    kf4ixm wrote: »
    ....the thing im not sure of it that the piezo speaker is capable of producing frequencies in that range....

    I really doubt you're going to get 30kHz out of a piezospeaker from the lab kit. You'll probably have to find a transducer with a center frequency in the 40kHz range.
  • kf4ixmkf4ixm Posts: 529
    edited 2010-09-19 09:26
    thanks erco, i did think about that, the dog not being able to hear it, but i really have no way to verify it, and i don't know of anyone that has one of these to test it. seems like i read somewhere that these piezo speakers are capable of up to 75khz, but from the spec sheets i've read, none tell what the frequency response of the element is. i will keep on looking though. our neighbor's dog like to bark at frogs and possoms at 2-3 in the morning, EVERY morning and it's getting old! and talking to the neighbor has done no good.:mad:
  • kf4ixmkf4ixm Posts: 529
    edited 2010-09-19 09:31
    ElectricAye wrote: »
    I really doubt you're going to get 30kHz out of a piezospeaker from the lab kit. You'll probably have to find a transducer with a center frequency in the 40kHz range.

    I also thought about that too, i have another piezo speaker in my stash o' parts that is around 1 3/4" to 2" in diameter. i'm going to try it and see if i have any better results. i was just wanting to verify what the actual freq. resp. is for these before i started digging.

    I didn't want to start 'barking up the wrong tree'!
    :lol:
    :smilewinkgrin:
    :rolleyes:

    Thanks for all the feedback guys, i really appreciate it!
  • LeonLeon Posts: 7,620
    edited 2010-09-19 09:55
    I was playing with those 40 kHz ultrasonic transmitters and receivers once and my cat could obviously hear the 40 kHz - he came over and investigated the source of the sound. It was useful; I knew that the transmitter was working, at any rate. :)
  • RavenkallenRavenkallen Posts: 1,057
    edited 2010-09-19 10:05
    I wonder if they can hear a PING))) sensor?
  • ElectricAyeElectricAye Posts: 4,561
    edited 2010-09-19 10:06
    This guy is driving a tweeter but he's doing so at 75 watts. Maybe you need that much power to make the unit do anything besides just cause the dog to bark even more?

    http://williamson-labs.com/sdi.htm
  • Tracy AllenTracy Allen Posts: 6,666
    edited 2010-09-19 16:06
    There are wideband transducers such as the Polaroid (Senscomp), which can produce (and also hear, as a microphone) frequencies from 20 to 80 kHz. The circuit is more complicated, because they require high voltage drive on the order of 100 or 200 Volts, plus a DC bias. They are not piezos.

    Ultrasonic piezo transducers are narrowband (like the one on the PING))) have a relatively sharp resonance and must be driven near their design frequency. Readily available frequencies are 25, 34 and 40 kHz. You could probably obtain good results with a mix of those frequencies or by driving ensembles of them at nearby frequencies to create beats.
  • FranklinFranklin Posts: 4,747
    edited 2010-09-19 18:50
    http://cgi.ebay.co.uk/PIEZO-CAP-TWEETER-ULTRASONIC-SPEAKER-60kHz-/200520143202
  • UnknownUnknown
    edited 2010-09-19 18:52
    Can't you run the piezo speaker frequency through an amplifier?
  • ElectricAyeElectricAye Posts: 4,561
    edited 2010-09-19 19:27
    Chuckz wrote: »
    Can't you run the piezo speaker frequency through an amplifier?

    The problem is this: piezo elements usually have strong resonances, which means they provide the largest amplitude (loudest sound) when driven at a very narrow band of frequencies. If you try to drive them at a frequency far away from their resonance frequency, their sonic output might drop to nearly zero, so it probably won't matter if you amplify the driving signal or not. Most piezo speakers you get at Radio Shack, etc. are designed to be used in the audible range, so they might have resonances around 3kHz or 5kHz, etc. To get up to 40kHz, you need something with its resonance in that region.
  • ercoerco Posts: 20,259
    edited 2010-09-19 22:01
    When you crack this code, please post your results. I also have an inconsiderate neighbor whose barking dog is driving my light-sleeper wife nuts. I wouldn't mind aiming a giant HF tweeter into his backyard pumping 1000W of 40kHz signal when his pooch barks at 2 AM. If it slowly cracks the stucco off his house in the process, that's a bonus!

    Edit: A friend of mine warns that even though we can't hear these high frequencies, we can still get hearing damage from them. So don't shove your ear against an apparently silent transducer.
  • potatoheadpotatohead Posts: 10,261
    edited 2010-09-19 22:54
    That's true.

    I once had a remote control car that used ultrasonics for the control scheme. The lower harmonic was right at the edge of human hearing.

    As a little kid, I could hear 22Khz. Verified it later in life, when I knew how, based on sources I heard earlier. Now it's sort of 18Khz, maybe 19 in the better ear, when it's clean, and it's really loud! (like that actually, because the little bit of roll off eliminates a lot of messy bits found in a lot of gear today) I'll bet it starts to roll off from the response it used to be, starting at 14 to 16Khz.

    Anyhow, the toy used a mechanical means to generate the signal, and it was actually LOUD, but just high in frequency. After listening to it up close a few times, my right ear rolled off it's high frequency response for DAYS. Came back, with a little tiny ring that faded after a considerable length of time.

    I never did it again, despite it being a very compelling sound! Almost nothing in life resonated at that range, and it was this nice, pure, really high tone :)

    Now, being older, I've a few ringers below 20db or so. Almost never hear them in ordinary life because the noise floor is often above that. When it's really, really quiet, there they are! --and slowly worsening, which is why I use protection religiously now --might just be an artifact of age. I suspect that, but am taking no chances at all.
  • kf4ixmkf4ixm Posts: 529
    edited 2010-09-20 12:09
    Thanks for all of the responses guys, im thinking i'll look for a tranducer of some type centered around 40-45khz, from what i've researched, anywhere between 30khz to 60khz is the range that dogs can hear, and that's what those devices emit. plus i will probably use either a transistor or mosfet output circuit to amplify the signal, again depending on the transducer i find and what kind of performance i can get out of it. i will post all findings as i gather them.

    Thanks again for everyone's time and effort in helping me silence the dog!:smilewinkgrin:
  • Spiral_72Spiral_72 Posts: 791
    edited 2010-09-21 07:07
    erco wrote: »
    I haven't gotten into ultrasonics, but piezo speakers definitely have resonant audio frequencies and are much louder at those freqs. Some dogs react more to those ultrasonic repellers, wonder if your dog can't hear, doesn't care or won't react. Maybe borrow a known working Barkoff unit and see if he reacts.

    My wife's dog either doesn't care, or can't hear these frequencies.... Too bad too, cause I was going to have some fun :) BWaaaAAAHAHAHA!!!
  • kf4ixmkf4ixm Posts: 529
    edited 2010-09-21 07:17
    found this one that seems to be what i need, not bad on the price either at $15.95.

    http://www.steminc.com/piezo/SMATR15F45H5.asp

    SMATR15F45H5.jpg
  • Duane DegnDuane Degn Posts: 10,588
    edited 2010-09-21 09:54
    Do you know what they mean by "Max. Input Voltage: 160 Vpp" ?
    Are you going to need some sort of transformer to use them?
    Let us know how it they work out.

    Duane
  • grenoblegrenoble Posts: 1
    edited 2011-09-01 18:21
    Hello,
    I clicked on the link above, on the steminc site, and that is not a piezo speaker.
    The part number SMATR15F45H5 is an Air Transducer and not a piezo speaker. You can use it to send and receive signals at a range of 2 meters. It works on the same principle of the sensors on the back bumper of cars. You can use them on robots as a directional device, distance sensors and frequency listening device.
    On the same web site I found the multi layer piezo speaker part number SMSPK2724300.
    This is a small size loudspeaker multilayer piezoelectric ceramic. This multilayer ceramic wafer is characterized by low operation voltage which makes it suitable for mobile applications such as cellular phones, gaming devices and others.
    I hope that helps. :smile:
    Regards
    Grenoble
  • Mark_TMark_T Posts: 1,981
    edited 2011-09-01 18:34
    grenoble wrote: »
    Hello,
    I clicked on the link above, on the steminc site, and that is not a piezo speaker.
    The part number SMATR15F45H5 is an Air Transducer and not a piezo speaker. You can use it to send and receive signals at a range of 2 meters. It works on the same principle of the sensors on the back bumper of cars. You can use them on robots as a directional device, distance sensors and frequency listening device.
    On the same web site I found the multi layer piezo speaker part number SMSPK2724300.
    This is a small size loudspeaker multilayer piezoelectric ceramic. This multilayer ceramic wafer is characterized by low operation voltage which makes it suitable for mobile applications such as cellular phones, gaming devices and others.
    I hope that helps. :smile:
    Regards
    Grenoble

    In ultrasonics you get transducers for solids/liquids and transducers for use in air (the extreme difference in acoustic impedance between air and solid/liquid means the same design of transducer cannot perform well in both situations).

    Air transducer is the scientific way of saying speaker (or microphone or both).
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