PUBLIC ADDRESS SYSTEMS 



119 



It may be interesting at this place to determine how successfully 

 these various units and the system as a whole fulfill the requirements 

 of equal sensitivity to all frequencies within the important speech or 

 music range. Fig. 1 shows the relative sensitiveness of the trans- 



100 



S(l 



iz 60 

 5 



>• 



3 40 

 K 



30 60 



120 240 480 960 1920 3810 

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Fig. 1 — 1-Condenser Transmitter with Associated Amplifier. 

 2-Carbon Transmitter without Amplifier. 



mitter as a function of frequency. The ordinates are proportional 

 to the logarithm of the power delivered for constant, sound pressure 

 at the diaphragm and the abscissae to the logarithm of the frequencies 

 employed. The lower of the two figures refers to the condenser 

 transmitter with its associated input amplifier. 6 The upper refers 

 to the push-pull carbon-type transmitter. These transmitters will 

 be described in detail later. 



Fig. 2 shows a similar curve for the complete amplifier system, 

 comprising a three-stage speech input amplifier, and a power stage 

 capable of delivering approximately 40 watts of speech frequency 



60 120 240 480 960 1920 3840 7680 

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Fig. 2 — Public Address System Amplifiers. 



6 The Sensitivity and Precision of the Electrostatic Transmitter for Measurement 

 of Sound Intensities. E. C. Wente, Physical Review, N. S. Vol. 19, No. 5, May, 1922. 



