Micro-perforated diffusors (MPD)
Micro-perforated diffusor with 7 stripes
Transparent micro-perforated diffusor in front of an exterior window of a recording studio
Detail view of the above MPD
Micro-perforated diffusors (MPD) consist of individual adjoining stripe-shaped micro-perforated resonators that are tuned to different resonance frequencies. In this way adjoining areas with different wall impedance are created that scatter incident waves diffusely, as is the case with phase grids of Helmholtz resonators.
The resonance frequencies of the individual stripes of a micro-perforated diffusor correspond to the same pseudo-stochastic sequences as are used in the construction of Schroeder diffusors. From an acoustical point of view the wells of the Schroeder diffusors with their different depths are λ/4 resonators. The depth of the wells is equivalent to a quarter of the wavelength of a sound wave exciting the resonator at its resonance frequency. With micro-perforated diffusors, micro-perforated resonators with the same resonance frequency are used instead of λ/4 resonators.
The scattering characteristics of micro-perforated diffusors are slightly worse than those of the associated Schroeder diffusors, but their necessary manufactured depth is considerably smaller. They can be made from many different materials, including acrylic glass.