A Research Of Reduce The Low Frequency Noise Of The Air Duct

[[abstract]]本研究以大眾使用之現況為量側條件，針對文獻所提之被動式噪音低減方法中之反應型及消散型消音器外，再依據狹縫裝置噪音控制之研究加以驗證，並參考噪音低減案例，進而以「試誤法」設計不同型式之隔板裝置，量測 1/3 八音度頻帶並分析探討其可改善方向，加以設計出適合一般小型風機之噪音低減裝置。 量測的頻率取樣範圍在 12.5 ~ 20k Hz 之間的 1/3 八音度頻帶範圍內，設定為無任何加權，再使用不同截面積、形狀、型式之隔板，設計不同之消音裝置，於不同距離下量測其消音效果，再與風速變化交叉比較，再評估及修正，以得最佳化之被動式消音裝置。 由本研究可得知，排氣風管出風口型式的改變，確實會改變出風量的大小及噪音的增減，而不同型式的消音隔板對不同頻率的噪音低減效果亦不相同。在實驗中，某些裝置雖然對噪音的低減成效顯著，但卻會使出風量顯著減少；狹縫裝置的驗證，雖然其在特定音頻有明顯降低，但過小的間隙卻造成高頻音(4k ~ 20k Hz)的增加。所以針對不同的噪音源必須先調查分析其頻率，再針對其特性選用不同種類之噪音低減措施與裝置，才能達到事半功倍的效果。[[abstract]]In this research we measured the 1/3 octave bands on condition that present populace use air blower refer to the formal study which is responding and dissipating types of inactive reducing noise method By testing and verifying the results by the research for slit device noise controlling refer to some noise reducing cases we designed different forms of partitions by the mistake test methods We measured 1/3 octave bands from different deigns and then discussed the possible improvement to design a noise reducing device suitable for the common small air blower The sampling ranges we measured was located between 12 5~20k Hz of 1/3 octave bands without any weighting We measured the noise absorbing effect of different noise reducing devices designed by using different partitions varied by surface area shapes and types in different distance and made a cross comparison with the changes of wind speed After evaluating results and amendment we could get the best way to install an inactive noise reducing device From the result we also found that the different types of exhaust of air duct will change indeed the exhausting wind volumes and increase and decrease of noise As well as the noise reducing effect in different frequency would be varied by different types of noise absorbing panels Although some devices could cause obvious noise reducing effects in our experiments but they would also lower the exhausting wind volume In the test of slit device the specific sound bands would be reduced by the small cap which could also cause the increase of sound in high frequency (4k~20k Hz) In conclusion investigation and analysis for the frequency of different noise sources should be carried out before adopting suitable measures and devices to reduce the different types of nois