Prediction of flanking sound transmission through cross-laminated timber junctions with resilient interlayers

While the low weight and high bending stiffness of cross-laminated timber (CLT) are key to its popularity, these properties also contribute to poor acoustic performance. Notably flanking sound transmission is a critical factor, driving the need for vibration reduction solutions such as resilient interlayers in the junction design. However, due to the complex material behavior of CLT and resilient interlayers, the improvement related to these solutions is difficult to predict. In this research, an analytical model with low computational cost is developed to evaluate the vibration reduction index $K_{ij}$ for CLT junctions with resilient interlayers. The CLT panels are considered as thin orthotropic plates with homogenized material properties. Three potential material models are proposed for the interlayer: it is considered as a thin plate, a thick flexible layer with out-of-plane motion governed by shear or distributed springs. The prediction model is experimentally validated for junctions consisting of CLT panels, with and without resilient interlayers. For junctions without interlayers, the predicted and experimentally determined vibration reduction index $K_{ij}$ correspond most closely when the junction is realized with stiff connectors. In this case, the predictions are moderately accurate with deviations below 5 dB in 1/3 octave bands up to approximately 2000 Hz for both corner and coplanar transmission paths. For junctions with resilient interlayers, the shear interlayer model exhibits the best performance with deviations of less than 5 dB in most 1/3 octave bands. For frequencies below 1000 Hz, the accuracy of the simplified spring model is comparable to that of the thick layer model. Simulations with equivalent isotropic material parameters yield slightly inferior predictions than for orthotropic parameters if the degree of orthotropy of the panels is high.