Sound absorbers including porous materials are used widely for noise control. The most widely-exploited and acknowledged absorption mechanism in porous materials is viscous friction due to relative motion between solid and fluid. Acoustical performance of woven (carpet) and nonwoven (felt) materials made of wool using a traditional technique was investigated. Absorption coefficient of felt was measured using standing wave tube method with and without an air cavity. Data were compared with predictions determined using the laws of Delany and Bazely. Very good agreement between data and predictions was observed. Sound absorption coefficients of both materials also were measured using an impedance gun technique over a wider frequency range. Absorption coefficient obtained using impedance gun method shows that the absorption coefficient of felt is higher than the absorption coefficient of carpet for mid and higher frequencies. Furthermore insertion loss (IL) of the felt was measured in a circular duct. It is found that felt can attenuate sound pressure level between 1 dB and 10 dB.
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机译:Buzzard Island Dredged material Beneficial Use access Road,Upper mississippi River,River mile 349,pool 20. General Design memorandum and Environmental assessment
机译:Natural (天然) and units (高单位) nutrients (营养素) 13 one component (成分) Total (综合) Vitality (活力) Samtoh, high natural nutritious foods (食品) of the name is excellent (优秀) a domestic natural raw materials (国产自然原料) using 12 species (利用) and processing (加工处理) and a method of manufacturing (制造方法)