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BELL SYSTEM TECHNICAL JOURNAL 



whole energy. In this figure the abscissae represent the d.-c. voltage 

 directly across the transmitter, the scale being logarithmic, and the 

 ordinates represent mean square contact noise or acoustic signal voltage 

 plotted in db above an arbitrary zero level. The experimental plots 

 for both signal and noise are straight lines but of .slightly different slope. 



m 30 



0.01 0.05 0.1 



APPLIED POTENTIAL IN VOLTS 



Fig. 3 — The mean square contact noise and signal voltages in a standard carbon 

 transmitter as a function of the d.-c. voltage on the instrument. The signal was 

 obtained from a constant intensity sound field. 



Analysis of the data shows that the mean square signal voltage due 

 to acoustic modulation is accurately proportional to d.-c. transmitter 

 voltage squared while the noise curve fixes the value of a at about 1.85. 

 In the case of the signal the square relationship is to be expected since 



