The fact that you can hear sounds around corners and around barriers involves both diffraction and reflection of sound. Important parts of our experience with sound involve diffraction. For instance, the TWEETER of a loudspeaker is shaped in the form of a fan for this purpose. Diffraction: the bending of waves around small obstacles and the spreading out of waves beyond small openings. Īs a result of their capability of diffraction, low frequency sounds are difficult to localize or contain in an environment (see CANYON EFFECT, DIFFUSE SOUND FIELD ).Īn acoustic radiator must be specially designed for good dispersion of high frequencies since this does not occur naturally through diffraction. Ĭompare: CANCELLATION, INTERFERENCE, PARABOLIC REFLECTOR, REFLECTION, REFRACTION. Thus, diffraction may aid sound dispersion and DIFFUSION. When the wavelength is similar to the dimensions of the object, as with low frequencies and buildings, or mid-range frequencies and the head, the wave diffracts around the object, using its edges as a focal point from which to generate a new wavefront of the same frequency but reduced intensity. Low frequency sounds have wavelengths that are much longer than most objects and barriers, and therefore such waves pass around them undisturbed. Currently, solid walls are used to provide partial acoustical shadows. Recent legislation, which limits allowable highway noise in adjacent communities, has stimulated interest in this problem. sound travels around a pillar (doesnt affect. The diffraction of sound around barriers partially defeats efforts to control noise by inter- ruption of line of sight. Such is the case with high frequencies with respect to the head, and thus is important in BINAURAL HEARING. how sound spreads around barriers or bends through an opening 2. High frequency sounds, with short wavelengths, do not diffract around most obstacles, but are absorbed or reflected instead, creating a SOUND SHADOW behind the object. Its about the collective motion of the air molecules, which translates to pressure waves in the air. 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. Sound is really not about air molecules hitting obstacles.
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