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Used DVM for SPL (Sound Level) Meter

Discussion in 'Electronic Basics' started by [email protected], Mar 6, 2007.

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  1. Guest

    Hi all, I have a nice DVM that has recording and PC interface and I
    would like to use it for a sound pressure level meter. I would not
    mind buying something that does this, but all I can find are complete
    units. Anysuggestion on how I can do this myself without getting into
    "yet another project"?

  2. Phil Allison

    Phil Allison Guest

    ** I gather you want to measure and log SPL readings over some period of
    time - right ?

    A great deal depends on what range of SPLs you need to be able to read and
    over what frequency range.

    DMMs are not sensitive to the tiny signals levels that typical mics deliver
    or to the highest frequencies in the audio band.

    More info on what you REALLY require will permit others to give good
    advice on cheap and simple solutions.

    ......... Phil
  3. Guest

    I am confused, what more do you need?

    I want to measure Sound Level. RS makes a meter that I can buy for
    $50. I already own a nice DVM. So why spend the $50? Is there anyway
    I can turn a DVM into a SPL Meter?
  4. Phil Allison

    Phil Allison Guest

    ** Go buy the damn RS one.

    Since you are not interested in " yet another project ".

    ........ Phil
  5. Eeyore

    Eeyore Guest


  6. Guest

    Hmmm, we'll I guess this is no effin good. What did you guys even
    get out of grade 8 electronics? Stupid Americans
  7. Bob Masta

    Bob Masta Guest

    Sure, just add a calibrated mic, mic preamp, A, B, and C weighting
    curve filters, a precision rectifier or true RMS circuit, a smoothing
    filter with adjustable time constants, and a log converter and
    *presto*, an SPL meter!

    Best regards,

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!
  8. Chris

    Chris Guest

    Chuck, you actually got a good set of responses from Phil, Graham and
    Bob (and I don't believe they're all from the US, either). It might
    have been a little brusque, but these guys are all very capable. The
    way you describe your requirement (i.e. not another project), it can't
    be done. Mr. Masta described exactly what you'd need to include in
    your project.

    Possibly if you learn a little more about SPL measurements, you'll
    understand why it's more complicated than just cobbling together an op
    amp or two:

    The Radio Shack Sound Level Meter (Catalog #: 33-2055, $49.99) is
    actually a pretty good deal for what you get. If you don't need
    automatic datalogging, I'd suggest you go that route. And if you do
    finally decide to cobble something like Mr. Masta's suggestion
    together, you could do worse than borrowing an RS meter to calibrate
    your project. Output readings on the one I got for a factory job
    several years ago compared pretty favorably above 75dB (A weighting)
    with an instrument costing about twenty times that much.

    If you do need datalogging, I guess you might want to rent or borrow
    one of those SPL meters costing twenty times more which have a DC
    voltage output proportional to reading, and just log that with your RS
    datalogging DMM.

  9. But then won't you end up with a bulkier package than the storebought
    sound level meter?

    And then won't it cost a fair percentage of the storebought sound level
    meter to get the parts for building it, especially for someone who doesn't
    have much of a background in electronics?

    The problem with people who "know something can't be difficult" is
    that they often don't know what's involved, so they think it should
    be really easy to turn a DMM into a sound level meter.

  10. Bob Masta

    Bob Masta Guest

    Ahh, my comments were all with tongue firmly planted in cheek! <g>
    I assumed he didn't know how difficult it was, and was trying
    to show that it was not at all simple.

    To the OP: If your goal is to own a nice portable SPL meter,
    the RS unit is a good deal, whether you get the digital model
    or the older analog one (if it's still offered).

    If you just need SPL measurements, my Daqarta package
    allows you to calibrate your sound card to do that. However,
    as you might imagine, you have to have a calibrated mic.
    Just getting one of these will cost more than the RS meter.

    So far, I've never found any good way to calibrate a mic
    other than by comparing to a known reference mic,
    or using a reference sound source. (There are some
    theoretical-but-impractical methods that work with
    certain kinds of mics, that don't require a reference.)

    Best regards,

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!
  11. ehsjr

    ehsjr Guest

    Your comment is uncalled for, and innacurate.
    Neither Phil nor Graham are Americans, and neither are

  12. Rich Grise

    Rich Grise Guest

    Sure. Get a calibrated mic, and measure its output voltage. You might
    want an amp of some kind, if it's a low-output mic (which the really
    classy ones usually are.)

    Then again, you might find that a decent mic costs more than the sound
    level meter - talk to the RS guy, and see if replacement parts are
    available - it's just a mic and a vu meter. - oh, yeah; vu meters have
    a log response.

    Given that, you might want to use your PC interface and some S/W to give
    you the log response, and calibrate the gain to read out directly in vu or

    Have Fun!
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