ON THE APPLICATION OF ACTIVE NOISE-CONTROL IN AN OPEN-END RECTANGULARDUCT WITH AND WITHOUT FLOW

The performance of the adaptive active control system in a relatively short open-end rectangular duct with and without air flow is investiga ted experimentally. Results show that the existence of broadband noise in the duct can reduce the sound attenuation level as high as 3 dB. F requency range of the attenuation is also reduced by the broadband noi se. The presence of air flow further reduces the performance of the sy stem. It is found that the centre of the duct cross-section is suitabl e for en or microphone location regardless the types of noise investig ated. The effect of downstream position of error microphone on sound a ttenuation depends on the nature of the noise to be attenuated. Result s also indicate that level of attenuation depends on the acoustic prop erties of the open end duct. The adaptive active control system in the present study is found to be not efficient at frequencies close to th e duct eigen frequencies. (C) 1997 Elsevier Science Ltd.