"Nathan Higgins" -spam wrote in message


I understand what a decibel is and how it is calculated, what I don't
understand is how sound level meters reference the sound to give a
reading in dB.

They convert sound into a voltage, measure that voltage, and compare that
voltage to a predetermined voltage that corrseponds to a certain very faint
sound level.

Surely every power meter would give a different
reading depending on what its reference is for 0dB.

To be standard they use the same reference for 0 dB.

I have the figure
0.02 mPa in my head as a reference but should all meters be
calibrated to this pressure ?

Yes. AKA

2 x 10-5 N/m2 at 1000 Hz.

AKA

10-12 W/m2

AKA
2 x 10-5 Pa

AKA

0.02 mPa

Is there a gentleman's agreement to
what 0db should be referenced to with sound meters (i.e.. to measure
audio in a concert).

Yes.