Any practical noise control device requires a combination of passive and active methods. Passive control rises absorption properties of materials to reduce high frequency noise but it becomes expensive in terms of weight and bulk at low frequencies, where attenuation must be achieved with active control. Active control is based on the principle of destructive interference between the primary and the secondary sources. The aim of this work was to design and implement a hybrid passive/active system to control the exhaust noise radiated by a small generator. The fundamental frequency of the radiated periodic noise depends on the electrical load plugged in to the generator. Passive control is afforded by a rectangular enclosure with dimensions (1000 x 710 x 530 mm3). The wall panels of the enclosure are made of steel, 1.5 mm thick, lined with a 30 mm layer of absorbing material. The Measured Insertion Loss is higher than 20 dB above 500Hz. Special attention is paid to technical aspects such as air refreshing and temperature inside the enclosure. Low frequency noise escapes the enclosure via air intake and exhaust openings. Active control, implemented in a feedforward commercial system, is used to reduce low frequency exhaust noise below 500 Hz. The reference signal is supplied by an accelerometer located on the air filter case of the generator. A high temperature loudspeakser is used as control source. Active Attenuation is achieved in the band (50, 500) Hz, with the fundamental frequency reduced as much as 35 dB.

4 pp.-- Comunicación presentada en: Joint Meeting "Berlin 99": 137th regular meeting of the Acoustical Society of America ; 2nd convention of the EAA: Forum Acusticum - integrating the 25th German Acoustics DAGA Conference. Berlin, March 14-19, 1999.

This work has been supported by the CICYT, Project AMB97-1175-CO3-01.

Peer reviewed