THE APPLICATION OF MICRO-PERFORATED PLATE S 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 she aring forces and so a relatively broad band absorber can be created wi thout using fibrous or porous materials. According to the conditions o f 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 measureme nts in a standing wave tube and in a resonator. With multilayered micr o-perforated plate absorbers (MPA), effective sound absorbers of broad band and relatively small construction depth can be produced. These h ave a wide field of application in room acoustics and in industrial so und protection.