Dispersion relation and sound transmission loss of a Mindlin plate with an array of attached masses

Abstract

The paper concerns increasing the sound transmission loss of wall partitions in the coincidence region by the addition of an array of point masses. Both theoretical and experimental analysis of sound and vibration attenuation in a Mindlin plate with masses attached in a periodic "supercell" pattern are performed. Distances between the neighbouring masses within the supercell are not restricted to be equal, and masses themselves can be non-identical. By modelling the masses as point attachments, analytical expressions are developed for predicting the dispersion relation and frequency bandgaps of the plate. It is shown that wave propagation in two primary (orthogonal) directions in the plate and the corresponding frequency bandgaps have the most pronounced effect on the sound transmission loss. Variation of the distances between the masses, or masses themselves, can lead to additional lower-frequency bandgaps. The effects of the frequency bandgaps on the sound transmission through the plate are validated by numerical analysis conducted using the wave and finite element method. Experimental testing in a transmission suite under diffuse field conditions of large-scale (2.4m by 1m) plates with periodically attached masses is conducted, showing benefits of utilizing multiple scattering to increase the sound transmission loss in the targeted region.