Active Noise Control Using Waveform Synthesis with Improved Convergence and Tracking

Abstract

Active noise control of periodic sounds, as commonly produced by rotating machinery, can be efficiently implemented using a synchronized waveform generator that produces a secondary signal necessary for noise cancellation. Synchronization of synthesized waveform is achieved by the use of reference tacho signal picked up by the magnetic or optical sensor. Waveform adaptation is performed in accordance with the residual noise signal after noise cancellation. Such approach for active noise control works well when a spectrum of offending noise is not changing much. However, during initial machine spool up, varying load and final spool down significant adaptability from waveform synthesizer is required to counteract changes in machine noise. In this paper, methods for improving convergence and tracking properties of waveform generator are presented and analyzed. An adaptive coefficient of waveform generator is modified in accordance to elapsed time during startup, varying frequency of the reference tacho signal and residual noise level. Results of simulations with different noise spectrum corresponding to various machinery rotational speeds are included.