Modex Broadband

Modex Broadband: The First Full Spectrum Metal Plate Absorber

Home Theaters and dedicated listening rooms often exhibit poor low frequency response with significant emphasis at modal resonances. Porous surface absorption is ineffective at these modal frequencies, because the air motion near walls and in corners is essentially zero, resulting in very low absorption efficiency. RPG developed its Modex™ Plate to address these problems. However, in addition to low frequency modal control, small rooms require mid and high frequency reflection control as well. We are extremely proud to introduce a new and unique addition to the Modex™ line, called the Modex Broadband, which complements the Modex™ Plate. The Modex Broadband was developed by the Institute for Building Pyhsics at the Fraunhofer Institute, and consists of a metal plate, embedded between two layers of damping material, surrounded by a perforated metal frame. The Modex Broadband offers broadband absorption effective from 50 – 5000 Hz in a thickness of only 4 inches. The Modex Broadband 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 changes everything. You will be astounded at the transients and clarity of sound once the Modex Broadband removes all of the masking low frequency reverberance. Now you can absorb more bass in less space!

Small rooms like Home Theaters and dedicated listening rooms often suffer from low frequency modal problems and also require mid to high frequency reflection control.Absorption at all of these frequencies has not been possible with a single acoustical surface treatment.


The Modex™ Broadband solves these problems by offering significant absorption between 50 and 5000 Hz in a surface depth of only 4 inches. The Modex™ Broadband represents a new generation of acoustic bass management.Now you can absorb more bass in less space!

rpg-modex-broadband-installThe Modex™ Broadband is installed by attaching metal “L” brackets to the boundary surface and sliding the panel and screwingn 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

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. The Modex™ Broadband consists of a freely moving steel plate 1 x 1.5 m sandwiched between porous layers . Both react together in a mass-spring manner offering absorption via three mechanisms. First,the metal plate provides pistonic absorption down to 63 Hz 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 up to about 125 Hz. 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.

Low Frequency Testing
Many published low frequency absorption coefficients are non-sense, becasue the accuracy of the absorption efficiency decreases at low frequencies in standard ISO 354 and ASTM 423 tests, due to inadequate diffusion. 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.