Hybrid noise control in ducts

Presented in this paper is a hybrid noise control system used to attenuate multi-tonal noise in ducts. The hybrid system is built by integrating active feedback noise control with adaptive-passive noise control. The adaptive-passive part of the hybrid noise control system attenuates the dominant tonal noise within the duct while the active noise control system attenuates the noise at other frequencies. To achieve such a hybrid system, the constituent technology for each noise control solution is extended. In particular, an algorithm is described for tuning adaptive-passive noise control devices in the presence of multi-tone noise sources. Also, a feedback controller design methodology is presented. This methodology, adapted from the robust control literature, is easily applied to uncertain acoustic duct systems possessing significant time delays. In the system studied, the time delay arises from the non-collocation of the microphone and the control speaker. The uncertain dynamics of the duct are due to the on-line tuning of the adaptive-passive element. The extended adaptive-passive and robust noise control technologies are combined into a hybrid system. Experimental results are included as are extensions to broadband noise sources.