On the application of active noise control in an open end rectangular duct 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 investigated experimentally. Results show that the existence of broadband noise in the duct can reduce the sound attenuation level as high as 3 dB. Frequency range of the attenuation is also reduced by the broadband noise. The presence of air flow further reduces the performance of the system. It is found that the centre of the duct cross-section is suitable for error microphone location regardless the types of noise investigated. The effect of downstream position of error microphone on sound attenuation depends on the nature of the noise to be attenuated. Results also indicate that level of attenuation depends on the acoustic properties of the open end duct. The adaptive active control system in the present study is found to be not efficient at frequencies close to the duct eigen frequencies.