In
an effort to provide full spectrum sound diffusion in
a single integrated diffusor, the self similarity property
of fractals was combined with the uniform scattering property
of the number theoretic reflection phase grating to produce
the Diffractal®, a patented diffusing fractal.
Problem
The bandwidth of a QRD® is limited at high frequencies
by the well width and at low frequencies by the maximum
depth. Additionally, wide area coverage with periodic
arrays focuses energy into certain diffraction directions.
A full spectrum diffusor offering wide area coverage is
needed.
Solution
 The
Diffractal® is the first diffusing fractal. It consists
of nested self similar scaled diffusors, each of which
covers a specific frequency range and offers wide area
coverage without lobing effects. A second generation
Diffractal® (DFR72) contains two nested QRD®s, thus
forming a diffusor within a diffusor. Each diffusor
provides uniform scattering over a specific range of
frequencies so that the effective bandwidth is extended.
The DFR72 can be nested within a larger low frequency
diffusor to provide wide area coverage, extended low
frequency diffusivity, and also minimum lobing associated
with periodic arrays. This third generation Diffractal®
(DFR73) offers low, mid, and high frequency diffusion
over an extended bandwidth, limited only by the depth
available.
Absorption
 (CLICK
GRAPH TO ENLARGE)
Diffusors essentially
scatter sound, but absorption may occur from wave resonances
within the wells when they are narrow and deep and viscous
losses due to pressure gradient induced air particle
flows between adjacent wells. The Diffractal® provides
high frequency diffusion without adding additional absorption
by replacing the mid frequency QRD® wells with nested
reduced scale high frequency QRD®s.
Diffusion
 (CLICK
GRAPH TO ENLARGE)
The nested diffusors comprising the Diffractal® extend
the high frequency diffusive performance beyond that
of the QRD® 734. The graph illustrates how the Diffractal®
mid frequency and high frequency nested components essentially
boot strap the uniform diffusion from 500 Hz to 20 kHz.
The diffusion coefficient is also compared to a flat
reflective panel which exhibits decreasing diffusivity
with increasing frequency.
Installation
The Diffractal® can be flush
mounted into an opening or surface
mounted on a wall or ceiling.
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Northampton, MA 01062 
