Out-of-band overshoot in narrowband active noise control system
Acoustic noise problems become more and more evident as increased numbers of large industrial equipment such as engines, blowers, fans, transformers, and compressors are being employed. Active noise control (ANC), in which additional secondary sources are used to cancel noise from the original primary source, has drawn considerable attention and shown significant promise. However, the performance of narrowband ANC systems is limited by out-of-band overshoot (one kind of the passband disturbance), which was first addressed in a 1991 study by Dennis Morgan. Although several methods for alleviating the out-of-band overshoot were presented in his study, practical limitations still remain. In this thesis, the out-of-band overshoot problem in narrowband ANC is comprehensively studied. One characteristic of the out-of-band overshoot, asymmetry, is analyzed from both mathematics and zero-pole placement theory points of view. An effective technique to eliminate the out-of-band overshoot, phase compensation, is presented. Computer simulations for verifying the theoretical results are also provided.