Active noise control of reverberant sound

The problem of active noise control of interior sound field is investigated. It is found that the direct sound is directional and is not subjected to active noise control, excepc the application of anti-sound sources as in case of noise sources in the open. While the reverberant sound field is a field of standing waves, a secondary sound source at the corner of the room may excite all the standing waves (normal modes of vibration), and hence is suitable for the suppression of the whole reverberant sound field after being modulated approprietely. Theoretical analysis and preliminary experiment confirm this prediction and encouraging results are obtained. The existing problems are discussed.