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Frequency Range for Piezospeaker — Parallax Forums

Frequency Range for Piezospeaker

bmcnichobmcnicho Posts: 40
edited 2014-04-24 07:50 in General Discussion
What is the frequency range for the piezospeaker that comes with the Boe-bot? A student asked me and I couldn't find the answer.

Thanks,
Diane

Comments

  • GenetixGenetix Posts: 1,754
    edited 2014-04-21 14:36
    The datasheet for the Piezospeaker can be found in this question asked by someone else:

    http://forums.parallax.com/showthread.php/140150-What-are-the-specs-for-the-piezo-speaker-in-Activity-Kit?highlight=piezo
  • Duane DegnDuane Degn Posts: 10,588
    edited 2014-04-21 15:23
    I recently wrote a program to play music with a piezo speaker. The notes go as low as 16.4Hz and as high as 7,902.1Hz. All these notes can be heard. The low notes sound more like clicks than notes.

    The short answer is pretty much any frequency you would want to hear and then some. The volume varies dramatically with different frequencies. It will be loudest at the resonate frequency. I don't recall the resonate frequency of the speaker but I'm pretty sure it's several thousand Hz.
  • potatoheadpotatohead Posts: 10,261
    edited 2014-04-21 23:13
    That datasheet does not provide a frequency range, nor a response curve.

    I seriously doubt that thing can actually reproduce meaningful sound under a couple of hundred Hertz. Reproducing low frequency sounds as clicks really isn't reproducing lower frequency sound as much as it is representing low frequency sound with higher frequency sounds.

    The resonant frequency is stated to be 4Khz. At that frequency, the response will be very high for an input signal. The response going from 4Khz to < 200Hz is going to be a fairly aggressive roll off, with some harmonic peaks at divisors of 4Khz, with response in the very low -db range at <200Hz and below. Meaning you won't move much air, but if you did somehow mechanically connect it to a bone in a solid way, those sounds might be heard.

    Toward the higher end, it's also gonna roll off some, but not in the same way, and those harmonic peaks will still be there. A little device like that should shoot well above 20Khz and still produce meaningful sounds.

    In terms of frequency range, it's something like 100-200Hz to 30Khz or so.

    Heh... If you PWM the thing, using something like a 30Khz carrier or maybe higher, you might really improve the lower end response. Just saying...



    In terms of response, somebody needs to find some better data, or graph it. Output at 300Hz is going to be a lot different than output at 2Khz, 4Khz, 8Khz, etc...
  • bmcnichobmcnicho Posts: 40
    edited 2014-04-24 07:18
    Thanks for your help. I'll tell my students to keep it between 1 kHz and 7 kHz. I just want to hear a discernible difference in a high, medium, and low pitch.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2014-04-24 07:50
    bmcnicho wrote: »
    Thanks for your help. I'll tell my students to keep it between 1 kHz and 7 kHz. I just want to hear a discernible difference in a high, medium, and low pitch.

    I think 100Hz doesn't sound too bad myself. I think potatohead's 100Hz to 30kHz range is about right.

    I started to make a video to record the various notes but my SD card was full. I may try again later today.

    Of course the students could program in various frequencies themselves and find an acceptable range they like.
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