Hybrid noise control in ducts

Presented in this gaper is a hybrid noise control system used to attenuate multi-tonal noise in ducts. The hybrid system is built by integrating activ e feedback noise control with adaptive-passive noise control. The adaptive- passive part of the hybrid noise control system attenuates the dominant ton al noise within the duct while the active noise control system attenuates t he noise at other frequencies. To achieve such a hybrid system, the constit uent technology for each noise control solution is extended. In particular, an algorithm is described for tuning adaptive-passive noise control device s 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 po ssessing significant time delays. In the system studied, the time delay ari ses 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 adapti ve-passive element. The extended adaptive-passive and robust noise control technologies are combined into a hybrid system. Experimental results are in cluded as are extensions to broadband noise sources. (C) 2000 Academic Pres s.