Patent GB-463766-A (GB)
Title: Improvements in or relating to apparatus for generating electrical waves corresponding to fluid medium waves
IPC: B06B1/06
Filed: 1936-06-27
Abstract: 463,766. Locating sounds. BRUSH DEVELOPMENT CO. June 27, 1936, No. 17911. Convention date, June 27, 1935. [Class 118 (ii)] [Also in Group XXXIX] Apparatus for determining the direction of sound waves comprises a microphone which generates electric waves in accordance with the difference of the pressure on two diaphragms or on the opposite sides of a single diaphragm and a second microphone which generates electric waves independently of the direction of the sound waves, the outputs of the generators being combined to give a bidirectional effect, that is to say, to represent the direction of the sound by the amplitude of the resultant current. In Fig. 6, the microphones have diaphragms consisting of flexible piezoelectric plates as described in Specification 409,040, [Group XXXIX]. Two microphones 1, la connected in parallel are employed, each having two pairs of parallel diaphragms 5, 5a, Fig. 5, and the pairs being spaced laterally there are two directions of incident sound giving maximum response. The non-directional microphone 2 has a pair of parallel diaphragms, and all the microphones are mounted together as a unit, as shown in Figs. 1, 2, having terminals 16, 17, 18. The output of the microphones 1, 1a is fed to a two-stage amplifier 21, 22 which by means of a condenser 29 and resist-' ances 27, 28a introduces a phase-lag of 90. The condenser 29 compensates for the greater response of the microphones 1, 1a as the frequency increases. The output of the microphone 2 is fed through an amplifier 30 to the combining transformer 34. For sound waves arriving from the left (Fig. 6), the output of the bidirectional microphones 1, 1<a> leads that of the microphone 2 by 280, and consequently the corresponding electric waves arrive at the transformer 34 with a phase difference of 180 and cancel if the potentiometer 28<a> is suitably adjusted. On the other hand for sound waves arriving from the right, the output of the microphones 1, 1<a> leads by 90 and the electric waves arrive at the transformer 34 in phase and give a maximum output. For intermediate directions, the output from the transformer 34 varies between these extreme values. Alternative dispositions of similar microphones are shown in Figs. 9, 10. Fig. 13 shows an analagous arrangement having a pair of laterally spaced condenser microphones 46 giving a bidirectional effect and a single non-directional condenser microphone 47, the outputs being combined as in Fig. 6. The last arrangement is modified in Fig. 19 by the replacement of the pair of directional microphones by a single condenser microphone 70 in which one condenser plate 73 is perforated to allow passage of the fluid medium, the vibrating plate 74 thus being influenced by sound waves on both sides. A similar arrangement shown in Figs. 15, 16 employs two bidirectional microphones 60, 60a connected in series and each having a single diaphragm consisting of a piezo-electric plate mounted so that sound waves impinge on both sides. The non-directional microphone 61 is similar to that employed in Fig. 6. Finally, a bidirectional microphone of the piezo-electric twisting type described in Specification 318,934, [Class 40 (v)], may be employed, in which a piezo-electric plate 84, Figs. 20,21 carries at two corners carrier blocks 90 supporting circular diaphragms 91. Sound waves produce a twisting flexure of the plate 84 which is proportional to the difference of the pressure on the diaphragms 91 and is therefore dependent on the direction of the sound waves. The circuits shown in Figs. 6, 13, 16 and 19 are provided with a switch .35 by which either the bidirectional microphones or the non-directional microphone may be cut out.