[Boatanchors] lcr meter question

[Brian Clarke]

Please don't use an LCR meter or an Ohmmeter to measure impedance or resistance 
of a microphone. In order to make the voice coil in a microphone as light as possible, 
extremely fine wire is used. 

A better way to measure to measure microphone impedance is to: 
  1.. Put the microphone in front of a loudspeaker driven by a constant oscillation, 
  2.. Feed the mic output to a CRO. You may have to use a pre-amp to get a useful display - make sure it's a high impedance input.
  3.. Put about a 100 Ohm resistor across the CRO input [or the pre-amp input] and a 5 k pot in series with the mic. 
  4.. Measure the Voltage on the CRO with the 5 k series R set at zero. 
  5.. Increase the series R till the Voltage seen on the CRO falls to half what you saw in the previous step.
  6.. Remove the series R and measure it; that's the approx impedance of your mic.
  7.. Repeat all steps at several different frequencies. Graph the results on log-linear paper. The results will be all over the place - most people quote the value at 1 kHz, but it does depend on what particular frequencies you want to use the mic for.
  8.. In practice, that's not the impedance you load the mic with - normally, you would use about 5 times that.
73 de Brian, VK2GCE.
  Yong Surk Lee said:


   I use the 1KHz to measure microphone or
  speaker impedances.