Absolute Calibration of Condenser Transmitters 



By L. J. SIVIAN 



Several methods have been used or proposed for the calibration of the 

 Wente condenser transmitter. The methods falling under the two classifi- 

 cations conveniently designated "constant pressure" or "pressure" 

 calibration and "constant field" or "field" calibration are most useful and 

 amenable to measurement. Which of these two calibrations is more 

 significant depends on the particular use made of the transrnitter. In the 

 following pages the methods now used or proposed are reviewed and the 

 advantages or disadvantages of each from the standpoint of transmitter 

 application are discussed. 



IN the original design of the Wente ^ transmitter the effective 

 diaphragm resonance was well above 10,000 c.p.s. The new design 

 (Western Electric No. 394-Type), developed by Wente, has an 

 effective resonance at approximately 5,000 c.p.s. It is about ten 

 times more sensitive (on a voltage-pressure basis), and more immune 

 from effects of humidity and of barometric changes. The important 

 external dimensions of the instrument are shown in Fig. lA . 



The response of the transmitter is defined as the ratio of the electro- 

 motive force generated to the acoustic pressure acting on the trans- 



BACKPLATE-^ 



Fig. L4 — Contour dimensions of No. 394-type condenser transmitter. 



Fig. IB — Contour dimensions of condenser transmitter used for field calibration. 



1 See bibliography. 



96 



