Three-dimensional MPP space absorbers: An overview of the project and recent development

A micro-perforated panel (MPP) is one of the most promising alternatives of absorbers for its durability, designability, and eco-friendliness. It is typically used with a rigid wall and air-layer between them, forming a Helmholtz resonator. However, this type can be used in limited situations. In order to use it more widely, various MPP space absorbers without any backing structures have been proposed. We proposed three-dimensional MPP absorbers (3-D MPA), i.e., a cylindrical and a rectangular MPP space absorber (CMSA and RMSA), which are superior to other absorbers in terms of wide possibility of arrangement: they can be suspended from the ceiling, or put on the floor. To make 3-D MPA useful for much wider range of applications, a trial production of a spherical MPP space absorber (SMSA) is made. In this paper, as a background the main results of CMSA and RMSA are overviewed. Then, the absorption characteristics of SMSA are measured in a reverberation chamber, and compared with those of CMSA and RMSA. As a result, SMSA shows a resonance peak at around 400 Hz: it is higher than CMSA and RMSA. The results show a SMSA can be used as a space sound absorber in practical situations.