GB1102186A - Improvements in and relating to microphone combinations - Google Patents

Abstract

1,102,186. Microphone circuits. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 17 May, 1965 [20 May, 1964], No. 20738/65. Heading H4J. Signals from a microphone or group of microphones M2 and from a microphone or group of microphones M1 are applied to an amplifier 1 and 2 respectively in opposite phase, the outputs of which are divided between two paths, one path of each pair being connected to a potentiometer 5. The slidable tap of potentiometer 5 derives a difference signal which is fed to RC filter 6, 7, amplifier 8, RC filter 9, 10 and resistor 11. Potentiometer 5 is adjusted so that, as regards incident sound in the main direction of the microphone combination, no signal is passed on. Any signal passing resistor 11 is combind with a signal from amplifier 2, and which passes an adustable resistor 12, amplifier 14 and resistor 26. The resultant difference signal is fed to a low-pass LC filter 23, 24, having a cut-off frequency of 1500 c/s., the lower frequencies being passed via resistor 25 to output terminals 30, 31. Signal-to-noise ratio of the difference signal is improved by an amplifier 8, and two RC filters 6, 7 and 9, 10 provide a flat characteristic. The directional characteristic may also be adjusted by a resistor 12. The output of an amplifier 14 is divided between two paths, one containing resistor 26, and the other containing an adjustable resistor 15. The signal passing resistor 15 is combined with the amplified signal portion passing the resistor 17 in the output of amplifier 1, and the resultant sum signal is amplified at 19 and fed to a highpass filter 20, 21 of cut-off frequency 1500 c/s., the higher frequencies passing to the output terminals 30, 31. Microphone combinations.-In one arrangement one microphone M2 (Fig. la, not shown), has on each side a microphone M1. Alternatively, two microphones M2 are in the centre of a straight (Fig. lb, not shown) or curved (Fig. 1c, not shown) line including eight microphones M1. In other arrangements, four microphones M1 are at the corners of a square with a microphone M2 at the centre (Fig. 2a, not shown). Alternatively, nine microphones M2 are centrally arranged with respect to four groups, each such group consisting of six diametrically arranged microphones M1 (Fig. 2b, not shown). In a further arrangement having an annular characteristic, a central microphone M2 is arranged between two pairs of microphones Ml (Fig. 3b, not shown). The outer two microphones M1 face in the opposite direction to the inner two microphones M1. The microphones may be of the cardioid type.