Sennheiser HMD120 Instructions For Use Manual page 12

For positioning the microphone of the HMD 120 headset, proceed as follows:
Adjust the length of the microphone boom so that the microphone is placed at the corner of
the mouth. To do so, loosen the quick-fixing device and adjust the microphone boom in length.
Pull the middle part of the microphone boom towards the mouth so that the distance between
microphone and mouth is approx. 2 cm.
Tilt the microphone for final positioning.
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