The Type 1 Modex Plate from RPG Diffusor Systems is a damped metal plate system, developed and patented by the Institute for Building Physics at the Fraunhofer Institute, and which delivers broadband low-frequency absorption, effective down to 50Hz. Small rooms often exhibit poor low frequency response with significant emphasis at modal resonances. To negate the effects of the latter, the Modex Plate utilizes 3 mechanisms to achieve its intended purpose.
Firstly, a metal plate provides pistonic absorption down to the lowest frequencies by vibrating against the "spring" of the porous backing. Second, the bending modes of the free-moving plate are heavily damped by the adhesive coupling with the porous backing, attenuating the lower mid-range frequencies. Lastly, mid-frequency sound waves diffract around the plate's edges to be dissipated in the passive porous absorber layer.
Together, these mechanisms offer an efficient, broad bandwidth, low-frequency absorber with a shallow profile of only 4 inches.