Physical classification and recent developments of active noise control systems

The rapid growth of the industry has a major effect on the environmental noise pollution, and it ranks second to the air pollution that adversely affects the human health. Passive noise control techniques are impractical and very expensive for lowfrequency noises. To solve such acoustic problem active noise control has been studied since early 20th century. Active noise control is based on the principle of superposition: i.e., it mitigates the unwanted noise by generating an anti-noise having the same amplitude but opposite in phase. In this paper, we present the physical classification of the existing literature on the basis of both noise source and quiet zone characteristics. Examples are point to point, point to zone, zone to point and zone to zone. We focus on the developing trends of active noise control in the last decade and discuss latest add-on features and multi-channel active acoustic shielding for open windows