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RPG Diffusorblox

In 1917, Straub patented the Cinder Block, the first concrete masonry unit (CMU). In 1965, slotted blocks were introduced to provide low frequency absorption. While useful for noise control, the flat or split face of these blocks actually creates reflection problems which degrade acoustics. This interference and their commercial appearance prohibit use in music and speech facilities.

In 1990, RPG® patented DiffusorBlox®, a unique, cost effective acoustical block. It provides an attractive interior finish treatment, plus extended low frequency absorption and sound diffusion to minimize interfering reflections.

Now for the first time in the history of architectural acoustics, a new acoustical concrete masonry unit offers unprecedented economy by making it possible to incorporate complete acoustical performance into the structural walls of music, speech, athletic, and multipurpose facilities. DiffusorBlox® simultaneously offer a distinctive appearance, extended low frequency absorption, sound isolation, and sound diffusive reflection control.

Now you can use CMU to effectively control noise over a wide frequency range. DiffusorBlox® are the only acoustical CMU to utilize two slotted Helmholtz resonator chambers, as well as the phase grating pressure gradient absorption mechanism to provide 100% absorption at 100 Hz. Painting reduces the high frequency absorption, but does not affect diffusion or low frequency absorption. Slotted and unfinished, stained or lightly painted DiffusorBlox® have a Noise Reduction Coefficient (NRC) of 0.85. Non-slotted and unfinished, stained or lightly painted DiffusorBlox® have a NRC of 0.75. Slotted and fully sealed DiffusorBlox® have a NRC of 0.41. Non-slotted and fully sealed DiffusorBlox® have a NRC of 0.40.   

Traditional slotted masonry offers low frequency absorption, but actually creates reflection problems which degrade speech intelligibility and corrupt sound quality. DiffusorBlox® solve this problem by uniformly scattering sound in many directions so the sound level in any one direction is minimized. Their shape is based on the reflection phase grating (RPG). These surfaces are designed using number theory sequences which insure uniform diffusion over a wide frequency range.


As noise pollution continues to escalate, we need powerful tools to reflect, absorb, and diffuse offending noise sources. DiffusorBlox® help environmentally by isolating noise sources like power transformers, HVAC, highway traffic, railroads, outdoor amphitheatres, airports, and machinery. 12'' slotted and fully sealed DiffusorBlox® offer a Sound Transmission Class (STC) of 55. This value means you can use DiffusorBlox® in the most demanding sound isolation applications, like movie theatres and recording or broadcast studios.  


  • QRD® sound diffusion
  • Two low frequency absorption mechanisms: Helmholtz and Pressure Gradient
  • High sound isolation
  • Distinctive textured appearance
  • Production by local block producers
  • Can be painted
  • Available as 305mm reinforced block and 200mm block
  • Available with or without low frequency absorption slots
  • Can be used with conventional block structural piers for high flexural strength
  • Structural and load bearing
  • Distinctive appearance permits use as an attractive finish treatment in architectural designs
  • Can be used for all noise control, speech, and music applications
  • Simultaneously offers structure, absorption, and diffusion in the same CMU, resulting in unprecedented economy

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