A SOUND PROJECTOR SYSTEM 



197 



There are in general two things one can do to avoid the harmful 

 effects of resonance in vibration transmitting or transforming appa- 

 ratus: (1) the period of resonance of each piece of equipment can be 

 moved outside the range of frequencies one wishes to transmit, at 

 the same time providing damping means to minimize free vibrations; 

 (2) the distortion produced by resonance in one piece of apparatus 

 can be compensated for or equalized by similar and opposite distortion 



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Fig. 1 — Reproducer for disc record. 



in some associated apparatus. The first is not always easy of practical 

 accomplishment in any particular device and generally results in an 

 instrument of very low inherent efificiency; the second usually involves 

 loss of energy. In both cases increased amplification is required. 



The sound record comes to the theater either as a wavy groove in a 

 composition disc or as a striated track of varying density at one 

 side of the picture film. It is the function of the apparatus being 

 considered to derive from these records an electric current in which 



