Microperforated diffusers (MPD)
Microperforated diffusers (MPD)
Microperforated diffusers (MPDs) represent a modern advancement of classic diffusing elements. They combine the principle of wall impedance variation with the space-saving design of microperforated absorbers. The result is a structure that effectively distributes sound waves without requiring the massive depth of conventional constructions.
Operating principle and structure
An MPD consists of several strip-shaped resonators arranged side by side. Each of these strips is microperforated and tuned to a specific resonant frequency. Similar to phase gratings made of Helmholtz resonators, this creates areas with different impedances that diffusely scatter incident sound waves in space.
The mathematical relationship to the QRD
Although they look completely different, MPDs follow the acoustic logic of classic Schroeder diffusers :
- Classic Schroeder diffusers utilize shafts of varying depths, which physically act as λ/4 cavity resonators.
- In the MPD, these deep shafts are replaced by flat, microperforated resonators, which, however, have exactly the same resonant frequency.
- The sequence of the different stripes is based on the same pseudostochastic number sequences as in QRD.
The decisive advantage: installation depth
While conventional low-frequency diffusers are often very thick, MPDs require significantly less space. This makes them ideal for rooms where every centimeter counts.
Materials and design options
A major advantage of MPDs is their material flexibility. They can be made from almost any solid material. Versions made of acrylic glass are particularly popular.
Practical tip: Transparent MPDs made of acrylic glass are ideal for use in front of windows (e.g. in control rooms) because they offer acoustic diffusion without interrupting visual contact or light penetration.
Note: Although MPDs are impressive due to their shallow depth, they exhibit slightly lower scattering properties than the massive Schroeder diffusers in direct comparison.