Bose QuietComfort Headphones utilise both active and passive noise reduction technologies. They use a sophisticated proprietary electronics approach for active noise reduction, placing microphones both inside and outside the earcups. The electronics system senses the sound in almost any environment and then measures, compares and reacts – instant by instant – to produce an opposing cancellation signal. Meanwhile, passive noise reduction is achieved by the combination of earcup fit, design and clamping force of the headband.