Optimisation of an active control system to reduce the exhaust noise radiated by a small generator

Abstract

In a previous paper (Cuesta M, Cobo P. Active control of the exhaust noise radiated by an enclosed generator. Applied Acoustics 2000;61(1):83–94) the authors reported a passive/active system to control the exhaust noise radiated by a small generator. Passive control was afforded by a steel rectangular enclosure lined with a layer of absorbing material. The enclosure, designed to provide the higher Insertion Loss, supplied attenuation higher than 20 dB above 500 Hz. To reduce the noise below 400 Hz, an active control system was designed with one reference, one error input and one control output. Whilst many harmonics in this frequency band were attenuated, the ANC system was unable to reduce some of them. The aim of this paper is to identify the origin of this lack of attenuation and to alleviate it. An exhaustive analysis of both the transfer function between the secondary source and the error sensor (the plant) and the reference signal has been carried out. A new ANC system with improved performance is described which controls all the harmonics until 300 Hz.