GB530483A - Improvements in or relating to sound translating devices - Google Patents

Abstract

530,483. Telephone instruments and circuits. ELECTRICAL RESEARCH PRODUCTS, Inc. June 26, 1939, No. 18521. Convention date, June 30,/1938. [Class 40 (iv)] A sound-translating device comprises the combination of a pressure-responsive moving- coil microphone 25 and a velocity-responsive microphone 49 arranged so as to have a substantially unidirectional response characteristic. The microphones have a generally coarsely curved exterior contour whereby each microphone allows sound waves to reach the other with a minimum diffractive effect. A casing 11 is mounted on a forked member 12 rotatable in a support 13 and the microphones are mounted within the casing by means of a bracket with arms 16 attached to the member 12 and upwardly extending brackets 18 to which the casing 27 of the moving-coil microphone is attached. The casing 27 is formed with a recess 54 in which is located a U-shaped magnet 40 which with a secured U-shaped magnet 39 is associated with pole-pieces forming an elongated gap for a ribbon diaphragm 49. The diaphragm is preferably corrugated near its ends and is convexly curved as indicated in Fig. 5. On the inner side of the gap 82 of the moving-coil microphone is located an apertured plate 83 carried by a sheet 85 of fabric. A flexible tube 37 connects the interior of the moving-coil microphone to the exterior to provide phase equalization at low frequencies. The casing of the moving-coil microphone houses an inductance 33, a transformer 31 and a condenser 34. In .the circuit arrangement shown in Fig. 4 the ribbon microphone is connected to the primary winding of the transformer 31 and the moving- coil microphone is connected to the secondary winding 68 provided with adjustable tappings 72 for varying the voltage output. The inductance 33 acts as a low frequency damping means for the ribbon unit and the circuit comprising essentially the condenser 34 and the tertiary winding 67 of the transformer is utilized to effect high frequency equalization by reducing the response of the ribbon unit at and above frequencies of say 3,000 cycles per second at which the moving-coil unit becomes increasingly directional. The switches 69, 70, 71 allow the units to be operated singly with or without the inclusion of the filter circuit. Specification 461,234 is referred to.