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Measuring sound pressure level

Discussion in 'Electronic Basics' started by Bubba, Oct 29, 2005.

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  1. Bubba

    Bubba Guest

    Greetings to all,

    I was thinking about building low-cost analog sound level meter, however,
    i am not sure how to get the non electrical value of sound pressure and
    transform it in electrical value. I planned to display the level with
    (cascaded) LM3915s', but was wandering about ideas of how to obtain sound
    pressure level in the first place.

    Thanks in advance!
  2. steamer

    steamer Guest

    --Howzabout using a speaker as the input device?
  3. mike

    mike Guest

    Google is your friend.

    You can get audio spectrum analyzer programs that run on your PDA to do
    that function.
    Plug a microphone into your sound card and download a free audio
    spectrum analyzer program.

    You don't say what test equipment you have, but using the sound card
    and replacing one function in the chain at a time will get you there
    in steps.

    Your most difficult problem is the LARGE dynamic range that
    the system has to handle. You'll end up with a bunch of range switches
    that make the project 10X more complex...not difficult, just complex.

    Wanted, Serial cable for Dell Axim X5 PDA.
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  4. Bob Masta

    Bob Masta Guest

    This is a non-trivial problem. You need a calibrated microphone to do
    this. Laboratory-grade "condenser" microphones which have stable
    performance are very expensive ($1000) and require 200 VDC supplies
    and special preamps. Instead, you can get a cheap microphone that
    has a calibration curve. Panasonic electret capsules come to mind,
    available from Digi-Key last time I looked. You will have to accept
    that the calibration will be crude at best, and will not last
    indefinitely. (Electrets lose sensitivity over time.)

    Be sure to get an "omnidirectional" model, since the "unidirectional"
    units generally have much poorer frequency response.

    The calibration information will consist of a frequency response
    curve (which for an omni electret will be pretty flat) plus a
    sensitivity value. A typical listing is "-62 dB +/-3 dB (0 dB =
    1V/ubar, at 1000 Hz)" For more information on how to
    use this to go from volts to SPL, see "Some formulas
    for working with sound" at
    Also a general discussion of dB at:

    Hope this helps!

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Home of DaqGen, the FREEWARE signal generator
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