. Elements of acoustical engineering. Electro-acoustics; Sound. 190 MICROPHONES. CONDUCTOR Fig. Pressure gradient microphone. gradient microphone consists of two pressure actuated units, separated by a very small distance, with the electrical outputs connected in opposition. Figure schematically depicts the essential elements of a pressure gra- dient microphone. A cylinder of mass 7n is coupled to a con- ductor located in a magnetic field. The cylinder is assumed to be the only portion of the system which will be influ- enced by sound waves. The diameter of the cylinder is assumed t
. Elements of acoustical engineering. Electro-acoustics; Sound. 190 MICROPHONES. CONDUCTOR Fig. Pressure gradient microphone. gradient microphone consists of two pressure actuated units, separated by a very small distance, with the electrical outputs connected in opposition. Figure schematically depicts the essential elements of a pressure gra- dient microphone. A cylinder of mass 7n is coupled to a con- ductor located in a magnetic field. The cylinder is assumed to be the only portion of the system which will be influ- enced by sound waves. The diameter of the cylinder is assumed to be small compared to the wavelength. Therefore, the average intensity will be the same for all points on the surface of the cylinder. The vibrating system is assumed to be constrained so that the only motion possible is one in a direction parallel to the longitudinal axis of the cylinder. Under these conditions the vibrating system is driven by the difference between the forces on the two ends of the cylinder due to the impinging sound wave. Assume a plane sound wave, from equation , the pressure, in dynes per square centimeter, at ;c = 0 may be written p = kcpA sin {kct) ^ 29 p — pm sin kct where c = velocity of sound, in centimeters per second, k = 27r/X, X = wavelength, in centimeters, p = density, in grams per cubic centimeter, yf = amplitude of , ct) = velocity potential, and pm = maximum sound pressure, in dynes per square centimeter. The pressure at the end of the cylinder xi = — A;c/2 for a direction of propagation 6 is (Ax \ f/ + — cos 6 J The pressure at the other end of the cylinder xo = Ax/2 is ct — cos d j 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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