A transfer matrix model to predict acoustic attenuation of earplug filters made up of elastic film and air cavity

The sound attenuation of earplugs, commonly used for noise protection, can be improved by adding acoustic filters. However, the effect of acoustic filters featuring an elastic film and cylindrical air cavities on sound attenuation needs to be better understood. This study seeks to predict acoustic attenuation of an elastic film filter via the development of an analytical model. Its advantage, as compared to numerical simulations, is to offer quicker solutions and a more profound comprehension of each physical parameter's impact. The total acoustic transfer matrix of the filter has been established by coupling the air cavity with the film under assumption of plane wave. The transfer matrix of the vibrating elastic film is based on the Kirchhoff-Love theory and could take into account all its dynamic behaviors, including possible in-plane tension. The model is then validated by comparison with numerical simulations using the finite element method. It is found that the plane wave assumption is valid in almost practical geometries of the air cavity such that the sound attenuation obtained from the analytical model align consistently with those from simulations. Potential limitations are addressed and evaluated.