The Type 2 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 low-frequency absorption down to 35Hz. 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, low-frequency absorber with a shallow profile of only 4.25 inches, suitable for spaces that have very low-end problems.