GB1233457A - - Google Patents

Abstract

1,233,457. Microphones. SONY CORP. 11 July, 1968 [13 July, 1967], No. 33120/68. Heading H4J. A microphone assembly comprises a wave type microphone 2 (Figs. 1, 3) incorporating an acoustic pipe 13 having a first microphone capsule 15 closing one end thereof and a gradient microphone 1 formed either of two microphone capsules 3, 4 (Fig. 1) or of the first microphone capsule 15 and a second independently mounted microphone capsule 3 (Fig. 3). The wave type and gradient microphones 2, 1 are so mounted that their directivity patterns coincide. A circuit includes filters arranged so that low frequency signals derived from the gradient microphone 1 are combined with medium and high frequency signals derived from the wave type microphone 2. Capacitor microphone capsules are preferably used although dynamic or ribbon type capsules may be employed. Microphone 1 1 comprises two similar capacitor microphone capsules 3, 4 (Fig. 1) each having a figure of 8 or unidirectional characteristic. Polarizing voltages are applied to capsules 3 and 4 from bias sources 6 and 7 through resistors 8 and 9 respectively. The D.C. biases on the capsules 3 and 4 are of opposite polarity to obtain a difference between the outputs of the capsules 3 and 4. The output of capsule 3 is connected through capacitors 10 and 11 to the gate of F.E.T. 12. The output of capsule 4 is applied to the gate of F.E.T. 12 through capacitor 11. Capacitors 10 and 11 block D.C. components. Wave type microphone 2 comprises pipe 13 closed at end 13a and having apertured members 14 filled with felt or other acoustic resistance material (16), Fig. 2 (not shown). Capacitor microphone capsule 15 is connected to polarizing source 6 through a resistor 20. The microphones are in a common housing 17. Capsule 15 is connected to the gate of F.E.T. 19. The drains of F.E.T.'s 12 and 19 are earthed through resistors 22 and 23 to provide source follower circuits. The output of microphone I is derived from the source of F.E.T. 12 and the output of microphone 2 is derived from the source of F.E.T. 19. The source of F.E.T. 12 is connected through a capacitor 24 to a low pass filter 25 and the source of F.E.T. 19 is connected to a high pass filter 26. The filters 25, 26 have approximately equal cut-off frequencies and their outputs are connected through a transformer 27 to terminals 28a, 28b. Sensitivity differences between microphones 1 and 2 are regulated by voltages applied to capsules 3, 4, 15 and to F.E.T.'s 12, 19. Alternatively (Fig. 3) capsule 15 serves as a portion of the gradient microphone 2 and as the wave type microphone 1. The output of capsule 15 is applied through high pass filter 26 and capacitor 18 to F.E.T. 19 and through a low pass filter 25<SP>1</SP> (identical with filter 25) to F.E.T. 12. The output of capsule 3 is applied to F.E.T. 12 through low pass filter 25 and capacitors 10, 11.