. The Bell System technical journal . s radial anduniform, uniform sound radiation still would prevail throughout thesolid angle subtended at the center of curvature by this portion of thesphere, provided its dimensions were large compared with the wave-length. Throughout this region the sound would appear to originate LOUD SPEAKERS AND MICROPHONES 269 at the center of curvature. Hence, for the ideal distribution of aspherical source within a region to be defined by a certain solid angle,it is necessary and sufficient that the radial motion be the same inamplitude and phase over the part of a
. The Bell System technical journal . s radial anduniform, uniform sound radiation still would prevail throughout thesolid angle subtended at the center of curvature by this portion of thesphere, provided its dimensions were large compared with the wave-length. Throughout this region the sound would appear to originate LOUD SPEAKERS AND MICROPHONES 269 at the center of curvature. Hence, for the ideal distribution of aspherical source within a region to be defined by a certain solid angle,it is necessary and sufficient that the radial motion be the same inamplitude and phase over the part of a spherical surface interceptedby the angle and having its center of curvature at the vertex andlocated at a sufficient distance from the vertex to make its dimensionslarge compared with the wave-length. If, further, these conditionsare satisfied for this surface at all frequencies, all points lying withinthe solid angle will receive sound of the same wave form. A horn wasdesigned to meet these requirements for the high frequency Fig. 5—Special loud speaker developed for auditory perspective experiment. 270 BELL SYSTEM TECHNICAL JOURNAL The horn, shown in the upper part of Fig. 5, comprises severalseparate channels, each of which has substantially an exponentialtaper. Toward the narrow ends these channels are brought togetherwith their axes parallel, and are terminated into a single tapered tubewhich at its other end connects to the receiver unit. Sound from thelatter is transmitted along the single tube as a plane wave and isdivided equally among the several channels. If the channels havethe same taper, the speed of propagation of sound in them is the large ends are so proportioned and placed that the particle motionof the air will be in phase and equal over the mouth of the horn. Thisdesign gives a true spherical wave front at the mouth of the horn atall frequencies for which the transverse dimensions of the mouthopening are a large fraction of a wave-length.
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
