Well balanced acoustical designs contain an appropriate combination of absorption, reflection, and diffusion. In many applications, however, limited budget or surface treatment thickness preclude the use of diffusion. Absorptive, fabric wrapped panels are specified for lack of an alternative. Unfortunately, wide area application may lead to an acoustically "dead" environment without "air" or ambiance. To solve this problem, RPG developed the first flat, zero depth diffusor: the Flatffusor. The Flatffusor simultaneously provides uniform sound diffusion at high and mid band frequencies and crosses over to pure absorption below the diffusive cutoff. The energy that is not diffused is absorbed.

To accomplish this goal, RPG developed a new planar 2 dimensional binary reflection amplitude grating consisting of a 31 x 33 element array of 1,023 half inch square absorptive or reflective areas. The reflective areas (black in upper illustration) map to the "1" bit and the absorptive areas (white) map to "0", or vice versa. The distribution of these resorptive binary elements is based on a 2 dimensional optimal binary sequence with a flat power spectrum. The resulting variable impedance surface forms a binary reflection amplitude grating suggested by James Angus. This surface is in contrast to RPG's reflection phase gratings, which use phase variation rather than amplitude variation to provide diffusion. The Flatffusor provides diffusion about an octave above the frequency whose wavelength is twice the size of the binary element. This explains the limitation of traditional variable impedance arrays. For example, 1' x 1' panels provide diffusion up to about 1 kHz. Remaining high frequency reflections would still corrupt speech and music quality.

The Flatffusor consists of a binary mask attached to the face of a semi rigid fiberglass panel. The panel is upholstered in a decorative fabric to completely conceal the acoustical functionality. The Flatffusor panel extends the acoustical performance of traditional absorptive fabric wrapped panels, allows wide area coverage without excessive deadening, and offers an alternative to RPG's line of traditional phase grating diffusors. The Flatffusor panel is ideal for any facility that needs reflection control from a decorative, upholstered, thin, and cost effective wall or ceiling panel.

Problem

Budget constraints and available surface depth for acoustical applications may prevent owners from using RPG's traditional number theory diffusors in their rooms, thus denying them the opportunity to realize the significant benefits of sound diffusion technology.

Solution

To overcome these problems, RPG developed the first economical flat diffusor called the Flatffusor. This new diffusor differs from the reflection phase grating (RPG) diffusors pioneered by RPG 15 years ago. Traditional RPG diffusors vary the phase of the incoming sound by reflection from 1 dimensional wells or 2 dimensional phase blocks whose depths are based on number theory sequences. The Flatffusor offers sound diffusion by varying the amplitude of the incident sound rather than the phase, forming a variable impedance, binary amplitude grating.

An optimal 2 dimensional binary sequence is used to determine the spatial positions of absorptive and reflective areas. The absorptive areas are represented by a 0 and the reflective areas by a 1. The sizes of the binary elements are less than half a wavelength of the upper frequency limit. The Flatffusor is designed to provide uniform diffusion between 1 and 16 kHz. This mechanism is an effective new innovation in offering sound diffusion from a flat surface.

The Flatffusor looks very much like a fabric wrapped absorptive panel, yet it provides an attractive alternative to RPG's furniture grade or molded diffusors.

Angular Scattering Response

For normally incident sound, the graph illustrates the angular response at 12.5 kHz. The flat reflector scatters sound primarily into the 90 specular direction. The wall mounted absorptive panel has similar response, only attenuated. The Flatffusor panel decreases specular scattering and more closely approaches the uniform ideal diffusion line.

The performance of a scattering surface is characterized by the diffusion coefficient, which is the standard deviation of the 1/3 octave angular response, shown here at 12.5 kHz for normal incidence. The graph illustrates how uniformly the Flatffusor scatters across the frequency spectrum, averaged over all incident angles, compared to a reflective panel.

Installation

Installation of the Flatffusor panel is quick and easy. Simply use construction adhesive or the supplied impaling clips to mount the panel to walls or ceiling.

If you can't find the RPG Diffusor System that you are looking for, please contact a Sound Pure associate for pricing and availability of your specific Acoustic Solutions.
Call toll free 888-528-9703, or email sales@soundpure.com

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