David Clark M-5B Microphone Overview:

The M-5B Microphone is a noise cancelling type designed to operate in place of carbon and amplified dynamic microphones. This microphone will not operate in circuits that do not supply a DC bias voltage. Most modern aviation communications equipment do supply this required voltage.

Microphone must be zero to 1/8" from lips for best signal to noise ratio (maximum noise cancellation).

David Clark part number 09168P-85 (also known as part number 09168P-82).  This microphone is on all of the David Clark One-X headsets and David Clark Pro-X2 headsets.

TECHNICAL DATA
DC Supply voltage and source resistance: 8-16 volts,
220-2200 Ohms – polarity sensitive
Type: Amplified Electret Microphone
Impedance: 150Ω Nominal
Microphone DC Supply Voltage:8 –16 volts, polarity sensitive
Sensitivity: 400mV ±6dB @ 1kHz for 114 dB SPL input
Frequency Response: 150Hz – 8kHz
Dimensions: 1.033” x 0.458” x 0.295”
Weight: 2g (0.071oz.)