In this paper the attenuation of sound propagation in an air-handling duct using robust and adaptive feedback active noise control strategies is investigated. The case of multiple narrow band disturbances located in distinct frequency regions and the interference occurring in the presence of disturbances with very close frequencies are considered. The active control uses a loudspeaker as compensatory system. The objective is to minimize the residual noise at the end of the duct segment

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... d. The system does not use any additional sensor for getting in real time information upon the disturbances. A hierarchical feedback approach will be used for the control of the system. At the first level a robust linear controller will be designed taking advantage of the knowledge of the domains of variation of the frequencies of the noise disturbances. To further improve the performance, a direct adaptive control algorithm will be added. Its design is based on the use of the internal model principle combined with the Youla-Kučera parametrization of the controller. Both robust and adaptive control require the knowledge of the discrete-time model of the secondary path (the transfer function between the control loudspeaker and the residual noise measurement) which is obtained by identification from experimental data. Experimental results on a relevant duct active noise control test bench will illustrate the performance of the proposed methodology.