Modeling, control and experiment of a feedback active noise control system for free sound fields

Feedback active noise control (FB-ANC) systems need no reference signal sensors and their implementation cost is therefore attractive due to the relatively simple configuration. This paper reports the design of an FB-ANC system for free sound fields by H∞ control theory based on a lower-order infinite impulse response (IIR) model of the acoustic plant. The acoustic plant, which is an acoustic transmission system from a loudspeaker (i.e. the actuator) to an error microphone (i.e. the sensor), is first devised by using the physical modeling method in conjunction with a system identification result. The feedback controller is next designed to attenuate the noise level in the vicinity of the error sensor by reducing the sensitivity function over the frequency range of interest. H∞ control theory is applied to achieve the control objective, because it can formulate the control specifications in terms of the frequency weighting functions in the frequency domain. Finally, the effectiveness of the proposed design procedure is demonstrated by experimental tests.