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. The phenomenon in SOUND PROPAGATION whereby a SOUND WAVE moves around an object whose dimensions are smaller than or about equal to the WAVELENGTH of the sound. The white region is a cross-section of the front part of an aircraft engine, the sound wave is produced by the turbofan. The higher-order the reflection, the further the wave has travelled and the. Second order reflections are like shots played off two cushions, third order off three etc etc. You can imagine the waves bouncing around like balls on a pool table. The animation below shows another example of diffraction. In small rooms, first order reflections tend to be loud and arrive very soon after the direct sound. 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. A shadow region is observed just behind the barrier (bottom right of the animation). 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). If the amplitude of the wave is larger than the size of the opening, then the wave will bend more to pass through the opening, and hence the wave will diffract more. The amount of diffraction depends upon the amplitude of the wave. 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. The following is the list of wave properties of diffraction that we are going to see in the topic:. 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. Taylor, F.RReceived 29 February 1940) This paper contains the results of some calculations which show the changes undergone by a sound pulse when it is diffracted by an infinite screen or wall with a straight edge. 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. Diffraction by a semi-infinite plane By F.
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