Classical active noise control technique

Abstract

A comprehensive theoretical investigation of a single input/single output (SISO) and a single input/multioutput (SIMO) active noise control system is presented. 'Classical' active noise control (CANC) where secondary sources act in antiphase with the primary noise source represents the bulk of this work. Previous studies concentrate mainly on the practical aspect of particular problems using analog devices without suggesting any algorithm that can be used to solve those problems using a PC. This was taken into consideration in the present study in which a digital model is developed and an algorithm is designed particularly to improve the noise reduction (NR) by taking into account the medium specification, the frequency response of the transducers (microphone and loudspeaker), the noise distribution and the separation distance between the sources. Two cases are studied. The first considers a single loudspeaker (SISO) and the second considers two loudspeakers (SIMO) which is known as Swinbank's source. The main results are: first, the ability for use with narrow band and wide band noise. Second, the transducers which were modeled as digital filters must have flat frequency response. Third, high degrees of noise reduction were obtained using multioutput devices. Fourth, the cancellation degree is a function of phase and amplitude for a single harmonic as well as the frequency of wide band noise. Fifth, a good noise reduction can be obtained over a long distance of the medium with accurate adjustment of the separation distance between the primary and secondary sources.