638 



BEl.L SYSTEM TECHNICAL JOURNAL 



TABLE IV 

 Calibration Constants 



(a) Constants of Vibrators I/D = 



( I ) Low frequency 5 / niilllamperes 



(2j Instantaneous power 286 \ per cm. 



(b) RectificT constant E- I = /iO (volts)-, niilliamp. 



(c) Pressure on transmitter vs. amplifier output p-/E' = 1/2.95' dynes-,'cni* volt'. 



(d) Power intrnsit\- at transmitter vs. pressure P, p- = 1 415 cm- microwatts dynes-. 



p- peessuKE IN PYNE.S/CM' on transmitteiz diaphrai^ 



E= VOLT ACiE OUTPUT OF AMPLIFIEfZ 



7000 ' 7O00 ' 3060 ' 3060' 



Fig. 6— Calibration of condenser transmitter with amplifier 



3O05 6060 



The product a b c d gives Pm/Z?m = 0. 192 microwatts per sq. cm. 

 of wave front as indicated by a deflection of 1 cm. of the oscillograph 

 low frequency vibrator. Similarly P,/I', = ll.l for the instantaneous 

 power \'ibrator. 



Method 



Records were made on sensitized paper strips G cm. wide mo\ing at 

 a velocity of about 20 cm. per second. Three graphs were traced 

 simultaneously, the instantaneous power, the mean power, and the 

 timing wave of 100 cycles from an oscillator. When connected speech 

 was being recorded, the oscillograph operator listened to the speech as 

 reproduced !)>• the loud speaker and punctuated the record at frequent 



