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.