![]() ![]() Numerical computations are carried out in full, giving the vector pressure ratio at the pole facing the source for spheres of various diameters and at various frequencies throughout the acoustic range. 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. Theory of the diffraction of a sound wave by a rigid sphere.-The theory of the diffraction of a plane wave of the type exp i ω ( t − x V ) by a rigid sphere is outlined in terms of Hankel's H 2 n + 1 2 functions, for which tables exist up to the highest orders required for the computations in practical cases. It is proposed to evaluate the correction for diffraction by employing a standard spherical mounting of which the diaphragm occupies a small area about the pole the increase in pressure for this mounting can be calculated theoretically, and the correction for other mountings can then be obtained by experimental comparison. All waves do this, including light waves, sound waves and water waves. ![]() Because of the mathematically irregular shape of the conventional microphone and its mounting the effect cannot be calculated. Diffraction is the bending of waves around obstacles or corners. Proposed method of evaluating the pressure correction made necessary by diffraction.-The diffraction of sound around the diaphragm of the microphone ordinarily used in the measurement of the instantaneous pressure in a sound wave causes the indicated pressure to vary from equality with the actual pressure in the undisturbed wave at low frequencies, to twice this pressure at high frequencies. ![]()
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