recordim; .1X1) Ri-.rRonrc/xc; oi- music and speech soi 



(.•k'ctroniagiU'lic recortlcr, which will lie (k'scribcd later, is designed to 

 work with this l\pc of system. With tiie exception (jf this electromag- 

 netic recorder, apparatus of this type has already been described in the 

 liti-rature.' In addition to this equipment which might be called the 



200 500 



FREQUENCr 



Fig. 2 — Calibration of tiie condenser transmitter and associated amplifiers 

 This curve shows merely the relative frequency sensitiveness of the system, the 

 zero line having been chosen arbitrarily. 



recording amplifier system, there is a volume indicator for measuring 

 the powder which is being dehvered to the recorder and also an audible 

 monitoring system. The audible monitoring system consists of an 

 amplifier whose input impedance is high compared with the recorder 

 impedance and a suitable loud speaking receiver. The monitoring am- 



/T 



u 



Fig. 3 — Schematic mechanical arrangement of diaphragm and air chamber 



plifier is bridged directh' across the recorder and operates the loud 

 speaking receiver so that the operator may listen to the record as it is 

 being made. 



"• Wente, E. C, "Condenser Transmitter as a Uniformly Sensitive Instrument for 

 Measuring Sound Intensity," Phys. Rev., Vol. 10, 1917. 



Crandall, I. B., "Air-Damped Vibrating Systems," Phys. Rev., Vol. 11, 1918. 



Wente, E. C, "Electrostatic Transmitter," Phys. Rev., Vol. 19, 1922. 



Martin, W. 1^1. and Fletcher H., "High Qualitv Transmission and Reproduction of 

 Speech and Music," Trans. A. I. E. E., Vol. 43,' 1924, p. 384. 



Green, I. W. and Maxfield, J. P., "PubHc Address Svstems," Trans. .4. /. E. E., 

 Vol. 43, 1923, p. 64. 



