The Original American Stereophone Company ,Ever since we invented the world's first SP/3 stereophone back in 1958, Koss Stereophones have been bringing back the excitement of a live performance. Music lovers around the world recognize that dedication to accuracy in sound reproduction as The Sound of Koss. ,The Koss QZ900 Noise Cancelling Headphones , ,QZ900 headphones are the latest addition to the Koss Quiet Zone line and add a new level of noise reduction, performance and comfort. The electronics package inside each ear cup is designed to monitor outside noise received through specifically mounted microphones in each ear cup. , ,Once this incoming noise can be analysed, the Koss QZ900 circuit introduces a sound wave that is 180 degrees out of phase with the incoming signal. The result is what Koss engineers term “zero earth” at the point of the eardrum. Most low frequency distractions from airplanes, lawn mowers, fans or even office hum will be dramatically reduced by these noise cancelling headphones. , ,Koss QZ900 noise cancelling headphones will create less reason to turn up volume and overdrive the tiny amplifier in your portable electronics. This means greater efficiency, less distortion, deep rich lows, and sparkling highs. , ,Unlike most other noise cancelling headphones, QZ900s play music with or without the active noise cancelling circuit engaged. A handy removable cord features an in-line volume control, and one standard AAA battery provides approximately 50 hours of active noise cancellation.