Adaptive Resonant Mode Active Noise Control

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 whenconsidering the active suppression of sound, feedforward and feedback. The former requiresthat the disturbance be known before the control signal is generated, and is ideal for periodicor random signals. Feedback arrangements, on the other hand, modify the dynamics of anenclosured 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 positionfeedback (PPF), can be applied to acoustic systems. In a previous study, a tuned resonantfilter modelled after a Helmholtz resonator was used in PPF configuration to suppress noiselevels by Bisnette and Vipperman (2004). However, the presence of speaker dynamics necessitatesfurther phase compensation, which is accomplished with an all-pass filter. The workpresented here further develops this control method by using a higher-order compensator. Inthis study, band-pass filters are used to improve the multi-modal control by limiting phaseinteraction of adjacent modes. Further refinements are made by realizing the control systemelectronically, which gives the ability to adapt controller parameters. Here, an algorithmis presented that adapts the resonant controller gain. Experimental results show moderatereductions with no energy spill-over to the next adjacent uncontrolled mode