Abstract
In this paper, the results of the measurements of sound absorbing characteristics of folding screen type perforated panel absorbents with porous materials are described. The measurements were made in our reverberation room of 169m^8 volume with an irregular pentagon shape. Following results were obtained. 1. The folding screen type perforated panel absorbents absorb nonselectively in the more broad frequency range than the absorbent with a constant air space. For example, the panels, perforation percentage p=6%, of the folding screen type walls show almost the same width of absorption curve as the panels of p=30% having a constant air space. 2. Now a days, the folding screen type walls are used frequently in an auditorium as the politriangular diffusors. In these types, the air space of them varies from maximum thickness L_1 to minimum thickness L_2 continuously. Thus, the perforated panel absorbent with this shape can be considered as a multiple parallel connection unit of many resonators, and the resonance frequencies are calculated by the formula [numerical formula] 3. In general, the characteristics curves of the measured sound absorption coefficient show the "flat" maximum part in the range between f_1 and f_2 calculated by above formulae. But, if p is large, the maximum part of the curve tends to shift towards f_1 rather than f_2.
