. The Bell System technical journal . compensating for this change of speed or static fluctuationby means of a delayed action compensator. This phenomenon is well-known in the mechanical governor art and is described by Trinks inhis book Governors and the Governing of Prime Movers. Theelectrical equivalent of this mechanical system is obtained by intro- SYNCHRONIZED SOUND PICTURES 191 ducing the condenser C2 in series with the high resistance Ri. When achange in current through the regulating reactance Li occurs thecorresponding change in voltage drop is not transmitted to the con-denser Co im
. The Bell System technical journal . compensating for this change of speed or static fluctuationby means of a delayed action compensator. This phenomenon is well-known in the mechanical governor art and is described by Trinks inhis book Governors and the Governing of Prime Movers. Theelectrical equivalent of this mechanical system is obtained by intro- SYNCHRONIZED SOUND PICTURES 191 ducing the condenser C2 in series with the high resistance Ri. When achange in current through the regulating reactance Li occurs thecorresponding change in voltage drop is not transmitted to the con-denser Co immediately, but C2 changes its voltage after a certaintime lag (approximately 1 second), required to charge the condenserthrough the resistance R4. The introduction of this time lag restoresthe precision of the circuit to the flat characteristic desired withoutintroducing hunting. Variable Speed Operation By throwing the switch Si to the right the operator can disconnectthe tuned circuit control and substitute a potentiometer Pi as a. Fig. 8—D. C. motor with control cabinet. source of grid voltage for tube V4. By means of this potentiometerthe operator can adjust the speed of the motor at any speed from900 to 1,500 corresponding to 68 to 112 feet of film per feature is employed for ordinary motion picture work where it isunnecessary to synchronize the picture with the sound. The regu-lation of the circuit under these conditions is sufiiciently good forordinary motion pictures. An interesting feature in this connection is that theaters in manycases have preferred to use the regulated speed position for ordinarymotion pictures as well as synchronized pictures. The reason forthis being that with the speed of the projector precisely controlledthe orchestra leader is better able to keep his orchestra in step withthe picture indicating apparently that closer speed regulation than is 192 BELL SYSTEM TECHNICAL JOURNAL at present provided would be desirable for ordin
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