Sennheiser NoiseGard HMDC 322 Instructions For Use Manual page 52

HMEC 302 headset:
Connect the ¼" (6.35 mm) stereo jack plug for the headphones and the PJ-068 jack
plug for the microphone to the corresponding jack sockets of your intercom.
HMEC 305 headset:
Connect the XLR-5 plug to the aircraft's XLR-5 socket.
HMEC 305-C headset:
Connect the XLR-5 plug for the headphones and the microphone to the aircraft's XLR-5
socket.
Connect the XLR-3 plug to the XLR-3 socket.
HMEC 306 headset:
Connect the 6-pin Redel plug to the corresponding socket in the aircraft.
HMEC 322 and HMDC 322 headsets:
Connect the U-174/U jack plug for the headphones and the microphone to the U-174/U
socket of your intercom.
Connect the XLR-3 plug to the XLR-3 socket.
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