The QZ900 is the latest addition to the Koss Quiet Zone line and adds a new level of performance and comfort. The electronics package inside each Koss QZ900 is designed to monitor outside noise received through specifically mounted microphones in each ear cup. Once this incoming noise can be analyzed, the Koss QZ/900 circuit introduces a sound wave which is 180 degrees out of phase with the incoming signal. In fact the noise canceling ability is so good in the new QZ900 that you'll find less need to turn up the volume and overdrive the tiny amplifier in your portable electronics. This means greater efficiency, less distortion and all the excitement of a live performance. The QZ900 operates with or without its active noise canceling circuit engaged.