. Elements of acoustical engineering. Electro-acoustics; Sound. HIGHLY DIRECTIONAL MICROPHONES 219 Employing mass controlled ribbon of mass m^, the velocity is given by A X = j2Tr/mr\ X A â kJT â 1 cos (27r//) cos B -(^)siâ â 1 sin 27r// cos This quantity is independent of the frequency and, as a consequence, the ratio of the generated voltage to the pressure in the sound wave will be independent of the frequency. The above discussion assumes that the lines are nondirectional. The directional characteristics of the individual lines of Fig. are given by equation The direction
. Elements of acoustical engineering. Electro-acoustics; Sound. HIGHLY DIRECTIONAL MICROPHONES 219 Employing mass controlled ribbon of mass m^, the velocity is given by A X = j2Tr/mr\ X A â kJT â 1 cos (27r//) cos B -(^)siâ â 1 sin 27r// cos This quantity is independent of the frequency and, as a consequence, the ratio of the generated voltage to the pressure in the sound wave will be independent of the frequency. The above discussion assumes that the lines are nondirectional. The directional characteristics of the individual lines of Fig. are given by equation The directional characteristics of the microphone, shown in Fig. , for D small compared to the wavelength are the product of equations and The directional characteristics may be written as ⢠^ (1 sm -(/ / cos 0 + d) R, = -(/ - Icosd + d) cos 9 The directional characteristics of the microphone shown in Fig. for various ratios of the length of the line to the wavelength for a delay of one quarter times the length of the line are shown in Fig. A measure LENGTH ='4A. Fig. The directional characteristics of the microphone shown in Fig. for a time delay of one-quarter the length of the line as a function of the ratio of the length of the lines to the wavelength. The polar graph depicts the output, in volts, as a function of the angle, in degrees. of the value of a line with progressive delay and a pressure gradient ele- ment for improving the directivity may be obtained by comparing Fig. with Fig. Employing these expedients approximately the same directivity can be obtained with a line of one quarter the length of the simple line shown in Fig. 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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