. Elements of acoustical engineering. Electro-acoustics; Sound. WAVE FRONTS" HIGH VELOCITY COOL AIR - LOW VELOCITY SURFACE OF THE EARTH SURFACE OF THE EARTH Fig. The refraction of a sound wave in air. density varies over the wave front. (See equation ) A sound wave may be bent either downward or upward depending upon the relative temperatures (densities) of the air,^ Fig. The distance over which sound may be heard is greater when the wave is bent downward than when it is bent upward. The first condition usually obtains during the early morning hours while the latter conditi
. Elements of acoustical engineering. Electro-acoustics; Sound. WAVE FRONTS" HIGH VELOCITY COOL AIR - LOW VELOCITY SURFACE OF THE EARTH SURFACE OF THE EARTH Fig. The refraction of a sound wave in air. density varies over the wave front. (See equation ) A sound wave may be bent either downward or upward depending upon the relative temperatures (densities) of the air,^ Fig. The distance over which sound may be heard is greater when the wave is bent downward than when it is bent upward. The first condition usually obtains during the early morning hours while the latter condition prevails during the day. Diffraction is the change in direction of propagation of sound due to the passage of sound around an obstacle. It is well known that sound will travel around an obstacle. The larger the ratio of the wavelength to the dimensions of the obstacle the greater the diffraction. The dif- fraction around the head is important in both speaking and listening. The diffraction of sound by microphones and loud speakers is important in the performance of these instruments. The diffraction ^ of sound by a sphere, a cube and a cylinder as a^ function of the dimensions is shown in Fig. These data may be used to predict the diffraction of sound by objects of these general shapes. As, for example, the sphere may be used to predict the diffraction of sound by the human head. ^ For other phenomena of atmospheric acoustics such as the effects of wind and temperature upon the propagation of sound waves and the applications to sound ranging and signaling in air, see Stewart and Lindsay, "Acoustics," D. Van Nostrand Co., New York City. 2 MuUer, Black and Dunn, Jour. Acous. Soc. Amer., Vol. 10, No. 1, p. 6, 1938,. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Olson, Harry Ferdinand, 1901-.
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