A virtual ANC headphone. (a) A quiet zone is formed in each ear by using a nearby secondary loudspeaker pair to reduce the sound in the ear, the required error-signal being determined from an LDV measurement of the vibration of a small membrane pick-up located close to the ear canal. Movement of the user is accommodated by a camera-based tracking system, which actively controls the galvanometer-driven mirrors to steer the laser beam and maintain its position on the membrane. (b) The locations of the secondary loudspeakers. Each secondary loudspeaker generates anti-noise signals through the ANC controller (not shown).