In places such as recording studios, movie theaters or concert halls, the walls are covered in panels that minimize echoes by scattering sound waves. Known as sound diffusers, they tend to be quite thick, using a lot of material and taking up a lot of space. Thanks to research currently being carried out at North Carolina State University and China's Nanjing University, however, such panels may soon only need to be about one tenth the thickness that they are now.
The most commonly used type of sound diffuser, the Schroeder diffuser, is made up of evenly-spaced square depressions that are identical in length and width, but that differ in depth. This arrangement is what causes sound waves that are hitting the panel to get scattered – by contrast, a perfectly flat, uniform surface would reflect the sound waves like light off a mirror, creating echoes.
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For regular Schroeder diffusers to work, their thickness has to be about half the wavelength of the lowest sound that they're required to diffuse – this can make them several inches thick, if not thicker. With the new version, however, their thickness only needs to be five percent of the wavelength.
As with traditional Schroeder diffusers, they're made up of a series of squares. Each square is actually an opening into an underlying shallow cavity, and the dimensions of those cavities are the same for every square. The openings themselves are different sizes, however. The end result is the same as using same-sized squares of different depths – the sound gets scattered, and echoes are avoided.
A paper on the research was recently published in the journal Physical Review X.
Source: North Carolina State University