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Measuring SPL — Parallax Forums

Measuring SPL

FrannyFranny Posts: 127
edited 2011-10-02 22:42 in BASIC Stamp
Hi, I need to be able to measure the level of a sound coming out of a mic preamp (at line level) It doesn't have to be high quality, all I need is a fairly accurate sound preassure level reading.

Thanks

Comments

  • ercoerco Posts: 20,257
    edited 2011-10-02 01:55
    Amp + ADC + Stamp, but that's a long row to hoe. There are easier/cheaper/faster ways.
  • LeonLeon Posts: 7,620
    edited 2011-10-02 03:16
    Then there is the calibration problem.
  • FrannyFranny Posts: 127
    edited 2011-10-02 06:15
    easier/cheaper/faster! And what would that be?
  • Mike4421Mike4421 Posts: 131
    edited 2011-10-02 13:54
    @ Franny.... if you have time to look around, try looking in the Nuts&Volts Achives 1994/5 and up in the Parallax Website, for some ideas and code samples for you project. Theres some neat projects there... like were the Basic Stamp2 to is connected to a phone line to make phone calls.... the schematics must be reviewed for todays use, so be carefull, if your not sure what or how it works, ask for advice at the forums again :)
  • W9GFOW9GFO Posts: 4,010
    edited 2011-10-02 14:17
    Are you sure that you need to measure SPL?
  • FrannyFranny Posts: 127
    edited 2011-10-02 14:32
    Yes, in other words I just need to measure how loud a sound is coming out of a preamp at line level so basically I need the ADC to BS2 part, I guess some kind of a cheap sound recorder would do but I don't even need it to record, I just need to compare different sounds to find the lowest one
  • W9GFOW9GFO Posts: 4,010
    edited 2011-10-02 14:58
    Sound pressure level is not measured in this way. It is the measurement of air pressure not voltage.

    There is a free iPhone app called JL Audio. It will measure SPL. I am sure there are others.

    If you want to measure the level just after the preamp - that is some kind of level - but it is not Sound Pressure Level.
  • FrannyFranny Posts: 127
    edited 2011-10-02 15:39
    Sound pressure level (SPL) or sound level Lp is a logarithmic measure of the effective sound pressure of a sound relative to a reference value. It is measured in decibels (dB) above a standard reference level.
  • W9GFOW9GFO Posts: 4,010
    edited 2011-10-02 16:12
    Franny wrote: »
    Sound pressure level (SPL) or sound level Lp is a logarithmic measure of the effective sound pressure of a sound relative to a reference value. It is measured in decibels (dB) above a standard reference level.

    Right. I'm not sure if you are agreeing or making an argument.

    Measuring the voltage after the preamp may give you an idea of the expected SPL, in the same way that measuring the voltage to a motor will give you an idea of the speed of the motor.
  • Peter KG6LSEPeter KG6LSE Posts: 1,383
    edited 2011-10-02 18:17
    GFO is right


    your meter may be right for a 100W amp feeding some book shelf speakers but a pare of ear buds would read the same in the meter bur not in real life ............


    you want a VU meter???

    http://http://www.national.com/mpf/LM/LM3916.html#Overview


    no offense to the BS2 but there are COTS chips that are really good at this ..

    If you do use a BS2 and a ADC be shure to cal it!!!!!!!!!.




    Peter
  • FrannyFranny Posts: 127
    edited 2011-10-02 21:00
    Good point, My bad, I'm not explaining myself well, Let's say you go in a room and take 20 snapshots of different spots and you don't even need to know the values, all you need to know is which one was the lowest one, That's it, So basically you guys are absolutely right, 99.99999% of the time you'd have to cal but in this case it doesn't matter what the value is relative to reality but just between those 20 snapshots you took, kinda like measuring the frequency responce of a room. So I went to the store and got an LM339, TL082, LM324, LM386N, anybody knows how to integrate any of these to the Bs2 ? Thanks for the help!
  • W9GFOW9GFO Posts: 4,010
    edited 2011-10-02 22:36
    Sorry Franny, what you said does make sense. When re-reading your post I noticed you said mic preamp - it did not get absorbed into my brain the first time through.
  • Mike4421Mike4421 Posts: 131
    edited 2011-10-02 22:42
    @ Franny... here is a link to the Original Scribbler Bot.... it uses a BS2 OEM = same but it has less pins on the board, but it has bigger through hole parts, cost less...... Down Load the Schematics near bottom of page....... then look at the speaker amplifier.... you can see how an LM386M is connected with resistors and caps to pin11...... dont for get to look at the Nuts&Volts Achives in the Parallax page for future/current ideas in projects.

    http://www.parallax.com/ProductInfo/Robotics/ScribblerRobotInformation/ScribblerRobotDownloads/tabid/458/Default.aspx
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