|Author:||Tsui, Kwong Lam|
|Title:||Improving sound transmission loss across ventilation window by active noise cancellation|
Ventilation -- Noise.
Hong Kong Polytechnic University -- Dissertations
|Department:||Department of Building Services Engineering|
|Pages:||ix, 76 leaves : ill. (some col) ; 30 cm.|
|Abstract:||Ventilation window, a window system formed by staggering the opening sashes of a spaced double glazing window, is a facade device to mitigate outdoor noise transmission and allowing natural ventilation simultaneously. The study conducted by Huang, Qiu and Kang  based on a scale down model found that applying active noise cancellation (ANC) technology can offer extra attenuation at low frequencies for the window system. This dissertation is a continuation of their study, which experimentally examines the improvement by ANC in the sound transmission loss across a full scale ventilation window under a realistic environment. With an optimized ANC system arrangement, an attenuation of 3.8dB at 200Hz was achieved and the frequency range of effective control was up to 800Hz under a periodic noise source, and an attenuation of approximately 5 dB was achieved in the frequency range of 103Hz to 125 Hz and the frequency range of effective control was up to 220Hz under a random noise source. The performances of the ANC system with different secondary source configurations were compared, and the best ANC performance was obtained by placing the sources on the inlet surface of the ventilation window facing to the primary noise source. Investigation on the relationship between the ANC system performance and the receiver room reverberation characteristic was also conducted. The experimental results show that a less reverberant environment in the receiver side favors an ANC system operation and enhances the system performance. The findings also reveal that the control signal feedback problem, the window's components resonance problem and the insufficient processing power of the ANC controller are the potential causes of control failures in a practical ANC system for ventilation window.|
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