Active noise control in a duct using output feedback robust control techniques

An active noise control (ANC) system generally uses speakers and microphones as inputs and outputs. The ANC is effective in regions around the error microphones, known as the zones of quiet. In this paper, a linear matrix inequality (LMI) based robust control method is used to enlarge the zones of quiet around the microphones. This is achieved by considering microphones to have fictitious uncertain locations around their nominal positions, and by designing a controller to guarantee robustness against all these location-based uncertainties. As a result, noise reduction in a wider region is achieved. The control is developed based on a non-minimal state-space realization (NSSR) scheme that allows one to generate an equivalent set of states for the ANC system, using only the measured inputs and outputs, without any differentiation. Actual hardware experiments using a digital signal processor (DSP) have been carried out to show the applicability of the method.