Acoustical Study of Micro- Perforated Plates for Vehicle Applications
Micro-perforated plate (MPP) absorbers are perforated plates with holes typically in the sub mm range and perforation ratios around 1%. The values are typical for applications in air at standard temperature and pressure (STP). The underlying acoustic principle is simple, it is to create a surface with a built in damping which effectively absorbs sound waves. To achieve this, the acoustic impedance of a MPP absorber is normally tuned to be of the order of the characteristic wave impedance in the medium (~ 400 Pa*s/m in air at STP). The traditional application for MPP absorbers has been building acoustics often combined with a so called panel absorber, to create an absorption peak at a selected frequency. However, MPP absorbers made of metal could also be used for noise control close to or at the source in many vehicle applications.