Costas Vlachos said:
OK, let's see what we have here. The meter scale is in dB, but the meter's
needle really measures voltage. We also have the following relation:
dB = 20 * log ( P / Po )
where P and Po are the two sound pressure levels we're comparing. So, if
you feed your meter with a voltage that is proportional to sound pressure
level (SPL), then the readings will be correct.
Hmmm, I shouldn't have used SPL in my reply above, as SPL has a fixed point
of reference. Please read the above as simply "sound pressure", *not* SPL.
So, if you feed your meter with a signal whose voltage is proportional to
sound pressure, then the readings will be correct. This is because of the
20*log relationship shown above. In addition to that, if your reference Po
is equal to a sound pressure of 20 microPascal (the threshold of hearing),
then the readings will be in dB [SPL].
Sorry for any confusion caused.
Costas