. Elements of acoustical engineering. Electro-acoustics; Sound. HIGHLY DIRECTIONAL MICROPHONES 215 acoustic resistance in the form of a long damped pipe, is used for trans- forming the acoustical vibrations into the corresponding electrical vari- ations. MAGNET LINE AXIS. Fig. Line Microphone. Useful directivity on the Hne axis. This microphone consists of a large number of small pipes arranged in a line with the distance from the opening of each pipe to the common junction decreasing in equal steps. The system is terminated in a ribbon element and an acoustic resistance. The contributio
. Elements of acoustical engineering. Electro-acoustics; Sound. HIGHLY DIRECTIONAL MICROPHONES 215 acoustic resistance in the form of a long damped pipe, is used for trans- forming the acoustical vibrations into the corresponding electrical vari- ations. MAGNET LINE AXIS. Fig. Line Microphone. Useful directivity on the Hne axis. This microphone consists of a large number of small pipes arranged in a line with the distance from the opening of each pipe to the common junction decreasing in equal steps. The system is terminated in a ribbon element and an acoustic resistance. The contribution, in dynes per square centimeter, by any element n at the common junction of the microphone may be expressed as D o (s. ^« ~ ^« cos d\ pn = Bn COS lirUt I + jBn sin 2x(// — ^{j ^71 ^71 COS ') ^ _ D 2Trjft2Tri{Xn-Xn COS 6)/\ where / = frequency, in cycles per second, / = time, in seconds, Xn = distance of the element n from the center of the line, in centimeters, X = wavelength, in centimeters, 6 = angle between axis of the line and the incident sound, and Bn = amplitude of the pressure due to element «, in dynes per square centimeter. In the case of a uniform line, with the strength a constant, the resultant when all the vectors are in phase is BJ, where / is the length of the line. The ratio Rg, of the response for the angle 6 to the response for 6 = 0 is 1 I /•^/2 Bnl \J-l/2 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, inc.
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