David Clark M-7/DC Microphone | 09168P-31
This Electret Microphone is a noise canceling type designed to operate in place of carbon and amplified dynamic microphones. It will not operate in circuits that do not supply a DC bias voltage. Most modern aviation communications equipment do supply this required voltage. If unsure, consult with your radio technical manual or with your local avionics shop. It is intended for use with wire booms.