I have an Aneng 8008 auto-ranging "true RMS" DMM with an AC mode that can measure mV. I have an unpowered lavalier microphone but when I put the probes on the ground and right or left contacts of the TRS plug, I have a voltage reading of 0.000 mV when I speak into the mic. Any idea what's going on? Or is it just impossible to directly test a microphone with a simple DMM?
If the microphone has a balanced output (TRS or XLR connector) you should not read any voltage between the ground (sleeve of TRS or pin 1 of XLR) and either signal lead, but you may be able to measure a small voltage between the two signal leads (tip and ring of a TRS plug, or pins 2 and 3 of an XLR connector) (I don't have a microphone handy to check - the voltage may be too low to measure with a DVM)