Active noise control products use electro-acoustical sound field modification or cancellation to attenuate or eliminate unwanted sound. By contrast, passive noise control products use materials to absorb sound. Active noise control products include controllers, sensors, actuators, and other electro-acoustical products for limiting or canceling noise or vibration. In a typical active noise control system, sensors are used to detect unwanted sound when it occurs. A controller and speaker are then used to create a sound field that is a twin of the unwanted sound, but inverted, so that it is a mirror image of the sound to be eliminated an anti-sound.