A SOUND PROJECTOR SYSTEM 205 



same as that at which the records are made, i.e. 90 feet per mhiute 

 in the case of synchronized sound and picture productions. By 

 throwing a switch the automatic feature may be cut out and the speed 

 of the machine may then be manually controlled by the operator. 



This completes the apparatus associated directly with the projector. 

 The general arrangement of the latest type of projection machine, 

 equipped with a Simplex head, is shown on Fig. 6. Incidentally this 

 projector is also arranged to be fitted with the Powers or the 

 Motiograph head. Fig. 7 shows a typical layout of a sound projector 

 system as installed for use with talking motion pictures. 



As in ordinary pictures, in order to run a continuous program, it is 

 necessary to use two projectors alternately. As the picture from one 

 machine is faded imperceptibly into that on the other so the sound 

 record may be faded from one machine to the other without the 

 audience being aware that a change has been made. At the end of 

 each record or sound film the music overlaps the beginning of the next 

 and a device called a fader is employed in making the transition. All 

 that is necessary is to turn the fader knob when the incoming machine 

 is started. This fader is in fact a double potentiometer. In the upper 

 or normal operating range the change in volume in moving from one 

 step to the next is hardly more than perceptible whereas in the lower 

 range used only in fading the steps are large and the volume decreases 

 to zero on one machine and builds up on the other very rapidly. By 

 choosing the proper step in the upper range one can obtain any 

 volume of sound desired within reasonable limits and thereby equalize 

 the level obtained from different sound records. The /ader is ordi- 

 narily installed with one or more auxiliary dials and handles inter- 

 connected so that it may be operated from any projector position. 

 In connection with the fader there is provided a switch for changing 

 from the film to the disc input system and also a key for switching a 

 spare projector in place of either of the regular machines. Fig. 8 

 shows a fader with one auxiliary position. 



Following the fader, we come to the main amplifier which raises 

 the energy of the feeble electric currents to a level adequate to supply 

 the loud speakers with sufficient volume to serve the particular 

 theater. Fig. 9 shows a typical amplifier panel. This combination is 

 capable of an energy amplification of about 100,000,000 times and is 

 so designed that all frequencies in the range from 40 to 10,000 cycles 

 are amplified practically equally. A potentiometer is provided on 

 the amplifier but while its handle is readily accessible it is ordinarily 

 not used after having once been set at the time of installation to give 

 proper results in the particular theater. Necessary adjustments are 



