. Elements of acoustical engineering. Electro-acoustics; Sound. DISPERSION OF SOUND 283 at the two points would be inversely proportional to the ratio of the squares of the distances from the reproducer. In this particular case, the difference in level would be 13 db. Obviously, such a large variation in sound in- tensity precludes the possibility of satisfactory reproduction over the entire area to be supplied. Therefore, a compensating means must be provided to counteract the variation of intensity with the distance from the repro- ducer. The directional loud speaker furnishes a solution of
. Elements of acoustical engineering. Electro-acoustics; Sound. DISPERSION OF SOUND 283 at the two points would be inversely proportional to the ratio of the squares of the distances from the reproducer. In this particular case, the difference in level would be 13 db. Obviously, such a large variation in sound in- tensity precludes the possibility of satisfactory reproduction over the entire area to be supplied. Therefore, a compensating means must be provided to counteract the variation of intensity with the distance from the repro- ducer. The directional loud speaker furnishes a solution of the problem. The directional characteristics of the loud speaker are shown in Fig. In this particular case, the difference of level for a point 40° from the axis,. --•^^E D C B A POSITION ON LISTENING LEVEL Fig. Arrangement of the loud speaker for a sound motion picture reproducing system in a theatre. The graph shows the intensity level at points along the Hstening level. as compared with the level at a point on the axis, is 13 db. The loud speaker is adjusted until the axis of the characteristic passes through the point E. Then the position of the loud speaker is adjusted until the angle 6 is. 40°. The distribution over the distance under consideration is shown in Fig. Summarizing, the variation of the sound pressure with the angle between the axis and the line joining the observation point and the reproducer has been employed to compensate for the decrease of the sound energy with the distance. From the response frequency characteristic of the loud speaker the pres- sure at any distance r centimeters on the axis may be obtained from the following equation. p=p. Xq 12 A. 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-. New York, D. Van Nostrand company, i
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