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Natural fiber-filled polymers offer good mechanical properties and economic competitiveness compared to traditional materials. Wood flour is one of the most widely used fillers, and the resulting material, known as wood plastic composite (WPC), has already found a wide applicability in many industrial sectors including automotive and building construction. This paper, as a followup of a previous study on a numerical-based approach to optimize the sound transmission loss of WPC panels, presents an extensive numerical and experimental vibro-acoustic analysis of an orthotropic panel made out of WPC boards. Both structural and acoustical excitations were considered. The panel radiation efficiency and its transmission loss were modeled using analytic and semi-analytic approaches. The mechanical properties of the structure, required as input data in the prediction models, were numerically determined in terms of wavenumbers by means of finite element simulations, and experimentally verified. The accuracy of the predicted acoustic performances was assessed by comparing the numerical results with the measured data. The comparisons highlighted a significant influence of the junctions between the WPC boards, especially on the panel&rsquo, s transmission loss. The radiation efficiency results were mostly influenced by the boundary conditions of the plate-like structure. This latter aspect was further investigated through a finite element analysis.

In this paper two prediction models to evaluate the radiation efficiency of orthotropic plates, developed with different approaches, are presented. A sound radiation model, based on an analytical/modal approach, is developed for a thin orthotropic plate, with the principal directions aligned with the edges. The model allows to consider the contribution of each mode, either resonant or non-resonant, as well as the influence of fluid loading on the plate dynamic response and on sound radiation. Moreover, a statistical model to evaluate the average radiation efficiency, based on a non-modal approach, which only considers the contribution of resonant modes, is presented. These two models have been used in order to predict the radiation efficiency of orthotropic cross-laminated timber (CLT) plates. CLT is an engineered wood material constituted by an odd number of lumber beams glued together, which have become very popular in the last twenty years in the building construction market. Due to their layered structure, CLT plates might exhibit a highly orthotropic behaviour. Both prediction models are validated by comparing the simulated results with the experimental radiation efficiency, obtained by means of vibro-acoustic measurements on three CLT plates. Finally, the influence of fluid loading on sound power radiated by CLT plates is investigated.