RPG® Modex Plate®

Small rooms often exhibit poor low frequency response with significant emphasis at modal resonances. This is especially true when they are sonically well isolated, due to massive boundary construction. Porous or friction based surface absorption is ineffective at these modal frequencies because the air particle velocity near walls and corners is essentially zero, resulting in very low absorption efficiency. Many bass absorption products on the market today are in fact porous material based products that can not possibly meet the specifications that they claim. For these reasons, RPG developed its Modex™ product line and is extremely proud to introduce a new and unique addition to this line, called the Modex™ Plate. The Modex™ Plate technology was developed and patented by the Institute for Building Physics at the Fraunhofer Institute, and consists of a damped metal plate system. The Modex™ Plate offers broadband low frequency absorption effective down to 50Hz in a thickness of only 4 inches, and 35Hz in a thickness of only 4.25”. The Modex™ Plate has an attractive powder coated metal finish and can be surface mounted on walls or ceiling. Every now and then a new technology comes along that can change everything. You will be astounded at the transients and clarity of sound, once the Modex™ Plate removes all of the masking low frequency reverberation. Now you can absorb more bass in less space!

Technology

Sound (1) strikes the steel plate (2) which pistonically vibrates (3) against the porous absorption spring (4), mounted on a rigid backing (8). The porous absorption also damps plate bending modes (5) and absorbs higher frequencies which diffract around the plate (6) through a perforated (7) metal frame.

Surface or corner applied porous materials lose efficiency at low frequencies, because the particle velocity or air movement associated with these long wavelengths is low. In order to maintain efficiency at low frequencies, the Modex™ Plate consists of a damped metal plate system. While the velocity is low, the pressure is at a maximum near the boundary and it is this pressure that is exploited in a mass-spring manner offering absorption via three mechanisms. First, the 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 proprietary adhesive coupling with the porous backing which attenuates the lower mid-range frequencies. Lastly, mid-frequency sound waves diffract around the plate’s edges to be propagated and thus dissipated in the deep passive porous absorber layer. Together, these mechanisms offer the industry’s first truly efficient, broad bandwidth low frequency absorber with a shallow profile of only 4 inches.

Absorption

Many published low frequency absorption coefficients are misleading, because the accuracy of the absorption efficiency decreases frequencies below 100Hz in standard ISO 354 and ASTM 423 test chambers, due to inadequate diffusion and modal density. Therefore, additional testing has been carried out at the Fraunhofer Institute in large scale impedance tubes with a cross section of 1.6 x 1.2 m and a special approach monitoring the decay times of the lowest axial modes in a 5x4x3 m room, with and without the sample present on one of the opposing surfaces. You can trust these data to be reliable and accurate.

Installation

The Modex™ Plate is installed by attaching metal “L” brackets to the boundary surface and sliding the panel over and screwing to brackets. Panels should be installed at high pressure locations. In order of highest to lowest efficiency, this would be the intersection of three boundary surfaces, two boundary surfaces and on one boundary surface.