The sound transmission losses (STL) of a metal panel with rib reinforcement (MPRR) are studied by both an experimental method and a simulation approach. The experimental method and data processing technique for obtaining STL are presented. Six MPRRs with different number of rib reinforcement and different geometry size of rib reinforcement, and six MPRRs with different type of the pasted damping material are designed and anufactured, and their STL performances are investigated by experimental method. The calculation model for STL of a MPRR is proposed and the calculated STL are compared favorably with the experimental data, which validates the proposed model. The analytical methods and conclusions are instructive for the design and the tuning of STL of MPRRs.

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The sound insulation of the front wall of a car is mainly used to isolate the noise of the engine from being transmitted to the passenger cabin. A front wall is generally a kind of structure of Absorber-Barrier-Absorber (ABA), where A is sound absorption layer and B is sound insulation layer. The sound absorption layer (A) usually consists of porous cotton of superfine fiber or microfiber. In this paper, kapok fiber is used to make the sound-absorbing layer A, and its sound absorption is compared with that of superfine fiber. Microstructure of the two fibers is compared, and it is found that kapok fiber has a large hollow structure. The sound absorbing coefficients of the layer A made with the two fibers are measured and it is concluded that the layer A made of kapok fibers can absorber noise greatly and thus has high sound absorption coefficient. The prototypes of ABA structural are made using two kinds of fibers as layer A, and the sound transmission loss (STL) was measured using reverberation room and anechoic room. The measurement shows that the ABA using kapok fiber as sound absorption layer has better sound insulations, and the STL of ABA using kapok fiber as sound absorption layer is increased by about 3 dB. A model for estimating STL of ABA structure is established and the calculated STL is validated. Using the developed model, the STL of ABA structures with different structural characteristics of Layers A or B is calculated and analyzed.

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