. Elements of acoustical engineering. Electro-acoustics; Sound. UNIDIRECTIONAL MICROPHONES 205 is the purpose of this section to consider the response of the unidirectional microphone as a function of the frequency and distance from a point source. The voltage output of a nondirectional microphone as a function of the distance r is given by snd = — sin oit r where Ri = sensitivity constant of the microphone, CO = 27r/, / = frequency, in cycles per second, r = distance, in centimeters, from a point source of sound, and / = time, in seconds. The voltage output of the bidirectional velocity
. Elements of acoustical engineering. Electro-acoustics; Sound. UNIDIRECTIONAL MICROPHONES 205 is the purpose of this section to consider the response of the unidirectional microphone as a function of the frequency and distance from a point source. The voltage output of a nondirectional microphone as a function of the distance r is given by snd = — sin oit r where Ri = sensitivity constant of the microphone, CO = 27r/, / = frequency, in cycles per second, r = distance, in centimeters, from a point source of sound, and / = time, in seconds. The voltage output of the bidirectional velocity microphone as a function of the distance and the wavelength X, in centimeters, is esD = -^2 { - sin w/ — -— cos co/ ) cos 6 \ r 2irr^ / where R> = sensitivity constant of the microphone, r = distance, in centimeters from a point source of sound, and 0 = angle between the direction of the incident sound and the normal to the ribbon. If the output of the unidirectional microphone as a function of the angle 6 is to be a cardioid of revolution for plane waves, then Ri must be made equal to R2. The ratio of the output of the unidirectional microphone as a function of the distance and frequency as compared to a pressure micro- phone is. y-e-s-o^ Response Ratio = j -^-^^ This ratio for 6 = 0, 30°, 60°, 90°, 120°, 150° and 180° for 1, 2 and 5 feet is shown in Fig. The same ratio for a conventional velocity micro- phone for 1, 2 and 5 feet is shown in Fig. It will be seen that the accentuation in the unidirectional microphone is smaller than in the case of the velocity 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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