![]() ![]() Sound waves can be diffracted around the corner under certain circumstances. Diffraction determines the direction in which most sound will be radiated, an important factor for the acoustical engineers who work to make them as quiet as possible. An important effect is sound diffraction. The white region is a cross-section of the front part of an aircraft engine, the sound wave is produced by the turbofan. The animation below shows another example of diffraction. Thus, this solution for noise reduction is efficient only if the houses are located within the shadow region of the sound barrier. It is characterised by low noise levels due only to the acoustic diffracted wave. Sound, on the other hand, has wavelengths that range from centimeters for high frequencies, down to meters for low frequencies. A shadow region is observed just behind the barrier (bottom right of the animation). If the hole is small, the waves coming through the hole will spread out (diverge) again, as if the hole were a point. Interference patterns due to the superposition of the incident wave and the diffracted wave are clearly seen just before the barrier (bottom left of the animation). Smaller holes cause waves to diffract more. The animation below illustrates how a travelling wave emitted from the upper left corner by, say, an aeroplane is diffracted by a sound barrier erected to shield homes from the traffic noise. An example of diffraction phenomena is given by the spreading of waves around an obstacle. Diffraction occurs if a wave encounters an object and if the wavelength is of the same size (or greater than) the object size. For the case of the point source at the axis. The spreading of waves when they pass through an opening, or around an obstacle into regions where we would not expect them, is called diffraction. Oblate spheroidal wave functions are used to formulate an exact solution for a very thin disk of elliptic profile.
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