Patent GB-1335522-A (GB)
IPC: G10H1/02
Filed: 1972-01-24
Abstract: 1335522 Reverberation systems L W PAVIA and C FARNY [trading as PAVIAFARNY ASSOCIATES] 24 Jan 1972 [21 May 1971] 3255/72 Heading H4R [Also in Divisions G1 and G5] A reverberation arrangement for connection to a sound system or to an electronic musical instrument, e.g. an electronic organ, comprises a reverberation device having connected in an input lead to it a variable resistance device shunted by a capacitor, the arrangement further comprising means for controlling the resistance of the variable resistance device. The variable resistance device is a pair of photoresistors, e.g. cadmium sulphide cells, connected in parallel, and the means for varying the resistance is a variable light source. The arrangement as shown in Fig. 1 is used in conjunction with an electronic organ 10 having an output amplifier 11 and loudspeaker 12. A reverberation device comprising electromechanical transducers 17, 18 coupled by springs 16 is connected in parallel with the speaker 12 and a capacitor 34 and photoresistors 33 are connected in parallel in one of the input leads to transducer 17. When the photoresistors are illuminated they have a resistance of about 25 ohms and short out the capacitor. When the photoresistors are not illuminated their resistance is of the order of megohms and the capacitor and the inductance of the photoresistors constitute a phase shift network and introduce a phase difference between the signals produced by the loudspeakers 12 and 21. By pulsing the photoresistors there can accordingly be obtained a celeste effect in the total sound, with the sound from loudspeaker 21 alternately reinforcing and cancelling the sound from speaker 12. The variable light source comprises a rotating disc 41 (Fig. 4, and Fig. 2, not shown) having areas of different translucency which is rotated between a light source 40 and the photoresistors 33a-33d. Either of the two pairs of photoresistors 33a and 33b or 33c and 33d may be manually switched into the circuit of Fig. 1. To produce sharp sound variations, e.g. when a large theatre effect is desired photoresistors 33c, 33d are used in conjunction with a mask 42 and a pattern of areas on the disc surface near its perimeter which pattern alternates 100% translucency with 0% translucency. Alternatively a different sound effect is obtained if the light pulses are not sharp, e.g. when softer and subtler sounds are required. For this photoresistors 33a, 33b are used in conjunction with a pattern on the disc which gradually changes in translucency. By arranging the photoresistors 33a, 33b as shown in Fig. 3, the two are not equally illuminated thereby adding to the gradually changing effect required. As an alternative to a rotating disc, an electronic pattern generator or relaxation oscillator may be used with the light source. Then a separate light source would be used for the different pairs of photoresistors. Where the organ has more than one output amplifier and speaker, one such arrangement may be used with each. Alternatively the outputs from each amplifier may be mixed and applied to a single arrangement. The reverberation device 16-18 is generally as described in U.S.A. Specification 2,230,836 wherein mechanical waves are transmitted along springs between two electromechanical transducers. U.S.A. Specifications 3,106,610, 3,405,223 and 3,564,106 are also referred to.