Active Control of Outgoing Broadband Noise Fields in Rooms

Active noise control system has been actively researched over the past half century, and implemented to reduce noises in ducts, headsets, and inside several automobile models. However, active control of noise fields, and specifically broadband noise fields, in rooms is still a barely explored topic due to the difficult of obtaining the reference signals, the challenge of online secondary path estimation, and the causal control constraint. In this paper, an active noise control system is developed that can cancel outgoing broadband noise fields in rooms. The proposed system decomposes the noise field on a sphere surrounding the noise sources into spherical harmonic modes, exploiting their directionality to generate the reference signals and remove the need for online secondary path estimation. A time-domain sound field separation algorithm and a time-wave domain adaptive algorithm allow the proposed system to meet the causal control constraint. Simulation results demonstrate that the proposed system can cancel broadband noise field globally in a room without suffering from the secondary source feedback problem.