ADAPTIVE RESONANT MODE ACTIVE NOISE CONTROL by

ADAPTIVE RESONANT MODE ACTIVE NOISE CONTROL Adam K. Smith, MS University of Pittsburgh, 2005 Low frequency sound waves propagating in a duct is ideally suited for active noise control (ANC) applications. Unlike passive treatments, ANC utilizes an acoustic actuator (loudspeaker) to cancel unwanted sound fields. There are two main control topologies when considering the active suppression of sound, feedforward and feedback. The former requires that the disturbance be known before the control signal is generated, and is ideal for periodic or random signals. Feedback arrangements, on the other hand, modify the dynamics of an enclosured sound field to augment damping, and requires no a priori knowledge of the disturbance. A modified version of feedback that is used in structures called positive position feedback (PPF), can be applied to acoustic systems. In a previous study, a tuned resonant filter modelled after a Helmholtz resonator was used in PPF configuration to suppress noise levels by Bisnette and Vipperman (2004). However, the presence of speaker dynamics necessitates further phase compensation, which is accomplished with an all-pass filter. The work presented here further develops this control method by using a higher-order compensator. In this study, band-pass filters are used to improve the multi-modal control by limiting phase interaction of adjacent modes. Further refinements are made by realizing the control system electronically, which gives the ability to adapt controller parameters. Here, an algorithm is presented that adapts the resonant controller gain. Experimental results show moderate reductions with no energy spill-over to the next adjacent uncontrolled mode.