Elements of acoustical engineering (1940) Elements of acoustical engineering elementsofacoust00olso Year: 1940 PRESSURE MICROPHONES 185 phones are aluminum alloys, Bakelite, styrol and paper. In order to obtain a maximum ratio of conductivity to mass, aluminum is almost universally used for the voice coil. Both edgewise wound ribbon and round wire have been used for the voice coil. See Fig. The diffraction of sound as a function of the angle of the incident sound by various objects shows that the sphere exhibits the most uniform direc- tional pattern (Fig. ). A spherical case with th
Elements of acoustical engineering (1940) Elements of acoustical engineering elementsofacoust00olso Year: 1940 PRESSURE MICROPHONES 185 phones are aluminum alloys, Bakelite, styrol and paper. In order to obtain a maximum ratio of conductivity to mass, aluminum is almost universally used for the voice coil. Both edgewise wound ribbon and round wire have been used for the voice coil. See Fig. The diffraction of sound as a function of the angle of the incident sound by various objects shows that the sphere exhibits the most uniform direc- tional pattern (Fig. ). A spherical case with the diaphragm located on the surface of the sphere seems to be the logical starting point for a non- directional pressure microphone. Referring again to Fig. , it will be seen that the microphone will show excess response over the range from 0° to 60° and will be lacking in response from 120° to 160°. This non- uniform response can be corrected by placing a disk, of semi-transmitting characteristics, of diameter equal to the spherical case directly above the diaphragm and spaced one-fourth inch. Employing this expedient, a non- directional characteristic ^^ is obtained for all frequencies. DIAPHRAGM } ^^ BOLT â unamrr^^'msif^ OF m, '-Ml râ, r^WfU'â1|âvwv CROSS-SECTIONAL VIEW 1000 FREQUENCY Fig. Cross-sectional view and the equivalent circuit of an inductor microphone. The graph shows the free space open circuit voltage response frequency characteristic. 2. Inductor Microphone'^'^ {Straight Line Conductor).âThe inductor microphone is another example of a moving conductor microphone. A cross-sectional view of this microphone is shown in Fig. The dia- phragm rmCuimx of this microphone is ' V ' shaped with a straight con- ductor located in the bottom of the ' V.' The equivalent circuit of this microphone is the same as that of the dynamic microphone in the preceding ' Marshall and Romanow, Bell Syst. Tech. Jour., Vol. 15, No. 3, p. 405, 1936. 12 Olson
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