Introducing the first acoustic dispersive prism

What is it about?

The acoustic prism principle inspires from to the optical counterpart: it splits sounds towards different angular directions depending on the frequencies, without resorting to complex signal processing techniques. It consists of a metallic bulk in which a small air-filled cylinder let air pass through. This air-filled duct then allows sound propagation as a conventional acoustic waveguide. But here the duct is splitted into small identical cavities, separated by each other by clamped elastic membranes, and connected to the outside through a series of 10 identical holes, in order to leak out sound waves propagating inside. Thanks to the arrangement of membranes, cavities and side holes, the sound celerity can be altered (slown down or accelerated) depending on frequency. According to the frequency of the propagating sound wave, the sound pressure delay arriving in each cavity can be controlled so that the waves will leak out from different holes with a controllable delay, thus directing the sound waves in a preferred direction. Listeners can catch the sound if they stand at the correct angle.

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Why is it important?

This is an unique design achieving an acoustic dispersive prism, that does not exist in nature. Signal processing techniques (beamforming) could allow directing sound waves in prescribed manner, but it requires several loudspeakers and signal processing hardware. Here the dispersion inside the prism is made by "natural" elements, and it requires only one sound source at the input of the prism.

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