Vergara E., Calçada M., Gerges S.

The porous materials are used for noise and vibration control in vehicles, industrial work, hearing protectors, etc. Structures are commonly lined with porous materials in order to increase the sound absorption and reduce sound transmission through multilayered systems. The sound propagation inside a porous material involves a quite complex process of interaction between solid and fluid phases. In this process occurs the sound energy dissipation due to thermal and viscous effects. The analytical models or numerical simulation are necessary to predict the systems noise attenuation before a prototype to be produced. However, these prediction models need the physical properties data of the materials involved in the production of these prototypes. An equivalent fluid model is adopted to model a rigid frame porous material. The sound propagation inside the porous medium is described in terms of its characteristic impedance and its wavenumber. These acoustic quantities are experimentally obtained by the two-thickness method in impedance tube. Also, the influence of the acoustic properties is evaluated for the impulsive noise attenuation of high amplitude and short duration using the shock tube technique with an impulsive noise generator to assess the parameters related to the sound attenuation of the hearing protector in the time and frequency domain.