Patent GB-488629-A (GB)
Title: Improvements in electrical apparatus for indicating the presence of certain frequencies in a complex sound
IPC: G10L25/90
Filed: 1937-01-08
Abstract: 488,629. Current and frequency measurements. COYNE, A. E. Jan. 8, 1937, No. 15702/38. Divided out of 488,502, [Group XXXVII]. [Class 37] Apparatus for indicating the presence of certain frequencies in a complex sound includes a number of mechanical circuit-controlling members selectively responsive to currents of different frequencies in ascending series. Fluctuating currents corresponding in frequencies to those of the complex sound are supplied to these members, of which those responding display distinctive signals either directly or through a relay. A series of tuning forks 1a, 1b, 1c, Fig. 1, of the kind described in Specification 488,502, are arranged in order of frequencies, the fork 1a being the lowest. The sound to be analyzed acts on a microphone 25, which is connected through an amplifier 26 to the operating coils 3 of the tuning forks. Each fork has a reed 15 arranged to give a bouncing contact so that when a fork vibrates it breaks the circuit of its corresponding relay 18 which releases its armature on to its back contact 20, completing the circuit of its signal lamp 19. At the same time the contact 27 is broken, thereby breaking the circuit of all succeeding tuning forks, so that an indication of the fundamental frequency only is given. In order to prevent a tuning fork of a harmonic frequency from giving a signal by continuing to vibrate after the sound has ceased and the fundamental fork has again closed its relay contact 27, a master relay 28 is included in the output circuit of the amplifier 26. This is traversed by constant direct current from the amplifier and attracts its armature when no sound is affecting the microphone, thereby breaking the circuit of all the signal lamps. In a modification, Fig. 2, each fork 1a, 1b, 1c, which is driven similarly to those shown in Fig. 1, has its own battery 24a, 24b, 24c, the positive terminals being connected together. A resistance 32, equal to that of one signal lamp 19, is connected as shown. If all the forks are at rest, all the signal lamps 19 are short circuited at the contacts 15. In this case the circuit of the battery 24b is through the resistance 32, fork la and a second bouncing contact 33a, fork 1b and contact 15b. The battery 24c has a similar circuit through the resistance 32, contact 33b, fork 1c, and contact 15c, current thus Rowing from all the batteries through the resistance 32. When a fork vibrates it opens its contact 15a, 15b, or 15c allowing its signal lamp 19a, 19b, or 19c to light, and also opens its contact 33a, 33b, or 33c, so that the circuit of lamps 19 associated with higher pitched forks is broken. In another modification certain of the relays 18, Fig. 1, have a pair of separate moving contacts, of which the first is in circuit with the energizing winding of the next fork and the second in circuit with the second moving contact of that fork, so that both the energizing windings and the signal circuits of the higher frequency forks are interrupted. The master relay 28 may have an auxiliary contact 28a controlling the application of damping pads to the forks. Switches may be provided by which each relay may be connected to the contacts of two of the forks the frequencies of which are, for example, an octave apart to facilitate the use of the apparatus in teaching the enunciation of sounds of given frequencies. Alternatively two tuning forks an octave apart may control a pair of lamps or other signals placed side by side. Where the range of each voice does not exceed an octave, forks an octave apart may be coupled to the same lamp, or electric filters may be connected in the microphone circuit to filter out the fundamental note. Tuned bodies other than tuning forks may be employed, or tuned circuits may actuate mechanical triggers or relays.