Anti-sound techniques enable acoustic and vibrational fields to be mimicked and cancelled bysecondary sources. That is, an unwanted sound can be suppressed if it can be completely reproducedin amplitude and phase over a required frequency range and over an area of required extent bysecondary sources. Devices for exploiting this aspect of linear wave fields has been experimented withfor over 50 years but it is only in the last decade that active noise control have emerged as a practicalpossibility as a result of the rapid development of electronic sensing processing techniques.