ELECTROMECHANICAL TRANSDUCER COUPLED TO A LOW INPUT IMPEDANCE TRANSISTOR AMPLIFIER AND YIELDING A FLAT RESPONSE OVER A GIVEN FREQUENCY RANGE

摘要

1,067,344. Capacitor transducers. STANDARD TELEPHONES & CABLES Ltd. Sept. 11, 1964, No. 37242/64. Heading H4J. A high reactive impedance electromechanical pressure-operated capacitive transducer has its electrical output terminals connected across a low resistive impedance means, and the transducer has a voltage output response falling with increasing input frequency so that the overall voltage output response of the arrangement is substantially constant over the range 300 c/s. to 4000 c/s. As described, a bipolar transistor amplifier (T1), Fig. 4a (not shown), with a gain of 100 and an input resistance 100 K ohms has connected to its input a capacitor microphone represented by a voltage source V in series with a capacitor C1 of 100 pf. The microphone is constructed to generate a voltage falling at 6 db./octave with increasing frequency in order to produce a flat overall output response of the combination within at least the frequency range 300 c/s. to 4000 c/s. The microphone comprises a diaphragm D (Fig. 6) of metallized plastics sheet spaced about 1 mil. from an insulated back electrode E which provides acoustic resistance. The electrode E is in the form of a perforated metal sheet, or sintered metal, or sintered dielectric particles carrying a metallized covering on its surface. A tube G leads into the case F to form an ambient pressure equalizer. The diaphragm and acoustic resistance are such that the acoustic resistance is larger than the reactance of the diaphragm over the working range. The polarizing charge is either built into the microphone in the form of an electret or supplied from an external source. The microphone may be used in a deaf aid or as a telephone transmitter feeding into a low resistive impedance of a transmission line.