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?

  • \$\begingroup\$ Is that the $20 10k count DMM? is it worth it? \$\endgroup\$ – dandavis Oct 26 '17 at 5:09
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    \$\begingroup\$ @dandavis they're astonishingly good for the money, but they're too light and the CAT is fake. \$\endgroup\$ – Neil_UK Oct 26 '17 at 5:25
  • \$\begingroup\$ You don't mention what the exact type and model the microphone is. You might think it has no electronics but the mics that are used the most are Electret mics and they need a DC voltage to work. Even if the mic was of the dynamic type (coil in magnetic field) then you'd have to SHOUT very loudly into the mic to get a reading a multimeter can measure. Signals from mics are very weak and DMMs are unsuitable for measuring them. \$\endgroup\$ – Bimpelrekkie Oct 26 '17 at 5:49
  • \$\begingroup\$ @Bimpelrekkie, how weak are the signals exactly? The multimeter's specs say it will do AC volts: 0.001mV to 750V & DC volts: 0.001mV to 999.9V. \$\endgroup\$ – fuzzybabybunny Oct 26 '17 at 6:06
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    \$\begingroup\$ Depends on how loud you shout and also the microphone. To measure the voltage properly you need an oscilloscope. Also the frequencies of the signals coming from a mic aren't suitable for most (especially cheap) DMMs. Most DMMs can only handle 400 Hz and lower. \$\endgroup\$ – Bimpelrekkie Oct 26 '17 at 6:12

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)

  • \$\begingroup\$ Interesting. Yes, it has a standard TRS output, but why wouldn't there be a reading? Isn't the voltage just a standard AC voltage in the millivolt range? \$\endgroup\$ – fuzzybabybunny Oct 26 '17 at 5:35
  • \$\begingroup\$ In a dynamic microphone, the microphone signal is between Tip and Ring (or pins 2 and 3), and is not connected to Ground/Shield (sleeve or pin 1). \$\endgroup\$ – Peter Bennett Oct 26 '17 at 15:58

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