THE APPLICATION OF MICRO-PERFORATED PLATES AS SOUND ABSORBERS WITH INHERENT DAMPING

By arranging a plate containing holes in front of an air cushion, the vibration of the air in the very small holes is greatly reduced by shearing forces and so a relatively broad band absorber can be created without using fibrous or porous materials. According to the conditions of use and the acoustic requirements, the mass, stiffness and inherent friction can be adjusted, largely independently of the plate material. Estimates from a PC program are in very good agreement with measurements in a standing wave tube and in a resonator. With multilayered micro-perforated plate absorbers (MPA), effective sound absorbers of broad band and relatively small construction depth can be produced. These have a wide field of application in room acoustics and in industrial sound protection.