Re: Measuring sound pressure level

On 29 Oct 2005 15:13:57 GMT, Bubba <nickname@xxxxxx> wrote:

>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.

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
www.daqarta.com/uuccunit.htm#yy01
Also a general discussion of dB at:
www.daqarta.com/gg00glos.htm#gg0a

Hope this helps!



Bob Masta
dqatechATdaqartaDOTcom

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

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