Noise cancelling headphones in ear headphones series sennheiser travel line sennheiser cx line type of fitting in ear transmission mode wired features in line control manufacturer specific features noisegard digital talkthrough sound functions passive noise reduction active noise reduction sound mode stereo sensitivity 111 dbmw impedance 42 ohm frequency response 20 21000 hz number of drivers 1 distortion factor 05 operating time 16 h length o