Why Diffusion?
Sound generated within a room will eventually strike a boundary such as a wall, ceiling or other surface in the path of the sound wave, and be reflected back into the room. Diffusion has the goal of controlling these reflections and redirecting sound.
While both absorption and diffusion have the effect of reducing sound intensity, diffusion preserves the sound and spreads it over a larger area, rather than having it disappear. The listener’s perception of an expanded space is created by the combination of its spatial and temporal components.
A perfectly reflective, smooth surface will absorb no wave energy, but return all of that energy back to its originating space. One example of a very reflective acoustic surface is a plaster wall.
A totally absorptive material will not reflect any energy back into the room. Materials that absorb sound are generally porous, fluffy and lightweight such as fiberglass insulation.
Diffusion simultaneously increases the distribution of sound, and modifies its direction (red line) without removing energy from within the space (spatial response). Also, the diffused sound energy is distributed in time (temporal response). Bookcases with random-sized books, and quarried stone (or shingled) walls have some sound diffusing properties.
Sound Prism
Over the years many shapes of sound diffusors and scattering devices have evolved. In the late twentieth century it was discovered that a panel with series of wells, would cause sound hitting its surface to be spread. This phenomenon is analogous to light’s behavior.
A butterfly’s wings may appear to be many brilliant colors when floating in the sunlight, only to be revealed as dull brown when observed up close. The color perceived is a result of the light being refracted as it bounces off of the small surface variations of the wing and breaking down into its component parts as if passing through a prism.
Smoke and Mirrors
The science of acoustical diffusion involves a lot of math, but it isn’t necessary to be a mathematician to understand and benefit from the use of diffusors. Taking a cue from the thought that some science seems to be smoke and mirrors, we used a fog machine and light reflection to illustrate diffusion.
The figure above shows a pair of parallel laser beams reflected from a flat mirror surface. Nothing changes other than their direction, opposite but equal.
The figure above shows an acoustical wall panel. Like sound entering the absorber, it vanishes.
In the figure above, a pair of laser beams is reflected off of D-series sound diffusor, with a custom mirrored finish. Four distinct beams leave where only two entered, each at lower intensity than the original beam and surrounded by additional blooms of light scattered and diffused by the mirror-surfaced elements.
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