Custom Audio Designs Ltd 

Bass traps | Broadband absorber | LF panel | Modex

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Modex Broadband Absorber 


Many 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 of 4" depth


The Modex Broadband solves the problems by offering significant absorption between 50 and 5000hz in a surface depth of only 4". The ModexTMBroadband represents a new generation of acoustic Bass management. Now you can absorb more bass in less space!

RPG is proud to introduce a new and unique addition to the ModexTMline, called the ModexTMBroadband. Broadband was developed by the Institute for Building Physics at the Fraunhofer Institute, and offers absorption effective from 50 - 5000hz in a thickness of only 4", The ModexTMBroadband has an attractive powder coated metal finish and can be surface mounted on walls or ceilings.



Surface or corner applied porous materials lose efficiency at low frequencies, because the particle velocity or air movement associated with long wavelengths is low.

The ModexTMBroadband consists of a freely moving steel plate 1x1.5m sandwiched between porous layers. Both react together in a mass-spring manner, offering absorption via three mechanisms.

First the plate provides pistonic absorption down to 63hz 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 125hz.

Lastly, mid frequency sound waves diffract around the plate edges and through the perforated sides to be propagated, and thus, dissipated in the deep passive porous absorber layer.

Together, these mechanisms offer the industries first truly efficient, broad bandwidth low frequency absorber with a shallow profile of only 4 inches.

Low Frequuency Testing

Many published low frequency absorption coefficients are nonsense, because 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 Institue in large scale impedance tubes with a cross section of 1.6m x 1.2m and a special approach monitoring decay times of the lowest axial modes in a 5x4x3 m room, with and without the sample present on one of the opposing surfaces.


The ModexTMBroadband is installed by attaching metal 'L' brackets to the substrate. The panel is then slid over and screwed to the 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.


  • Size - 1m x 1.5m x 100mm.
  • Model number 30/1/70
  • Weight 70lbs.
  • Finished in white powder coating.
  • Predrilled 'L' shaped metal mounting brackets supplied for easy installation.

All information contained in these details is given in good faith but without warranty.
Custom Audio Designs reserves the right to alter the specifications of any product without notice.
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