Conference_programme: 1: Absorbing materials
Lecture: Sound Absorbing Characteristics of Granular Material Multi-divided by Membranes supported by Rigid Frame
Author(s): Tsuruha Takumasa
Summary:
This paper investigated techniques to control the sound absorbing characteristics of granular materials without changing thickness. The multi-divided structure of granular materials was proposed, which is granular materials multi-divided by membranes that are supported by a rigid frame. This structure was designed to apply no static load of the upper layer to the lower layer. The normal incident sound absorption coefficients of two types of specimen, namely non- and multi-divided structure of hollow glass beads, were measured using a cylindrical acoustic tube. For the non-divided structure, the first peak frequency of the sound absorption coefficient shifted toward a lower frequency side as the thickness increased. When the thickness further increased, the shift of first peak frequency became smaller. The first peak frequency of the multi-divided structure appeared at a lower frequency than that of the non-divided structure of the same thickness. In addition, the first peak frequency shifted toward a lower frequency side as the number of division increased. The first peak frequency was calculated from the effective mass and the apparent dynamic stiffness for the granular materials. The effective mass was evaluated by the effective axial stress inside the granular materials filled in a container. The apparent dynamic stiffness of the multi-divided structure was evaluated as a series connection of the dynamic stiffness of each layer. The calculation of the first peak frequency was almost in a good agreement with the experimental results with respect to the multi-divided structure.
Corresponding author
Name: Mr Takumasa Tsuruha
e-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.
Country: Japan
