Layered Fibrous Treatments for Sound Absorption and Sound Transmission

摘要

In this paper, evidence has been presented to support the assumption that light fibrous materials can be modeled asbeing limp. A new porous material theory has been developed to specifically account for the small bulk stiffness ofthese media. That model has been shown capable of reproducing the predictions of elastic porous material models,but at significantly less computational expense, and without the risk of numerical singularities tbat occur when thebulk stiffness in the elastic model is made smalt. The limp model presented here has a simplicity comparable to thatof rigid porous material theories, but in contrast to the latter, accurately accountS for a fibrous material’s solid phasemotion, and is hence more accurate, particularly when used to predict the transmission loss of multi-layer systemsincluding fibrous layers. Both the limp model and the transfer matrix method presented here were experimentallyverified as useful tools for predicting the acoustical properties of layered treatments: thus they may be used withconfidence to optimize acoustical materials. Finally, and perhaps most importantly, it was found that there exists anoptimal flow resistivity for a limp fibrous material of given thickness and basis weight, and that the optimal flowresistivity depends on the application considered: i.e., whether absorption or transmission loss is being optimized.