LOUDNESS 



391 



We can now express the data in Table I in terms of field intensity 

 levels. To do this, the data in each double column were plotted and a 

 smooth curv^e drawn through the observed points. The resulting 

 curves give the relation between voltage levels of the pure tones for 

 equality of loudness. From the calibration curve of the receivers 

 these levels are converted to intensity levels by a simple shift in the 

 axes of coordinates. Since the intensity level of the reference tone is 

 by definition the "loudness level," these shifted curves wiU represent 

 the loudness level of pure tones in terms of intensity levels. The 

 resulting curves for the ten tones tested are given in Figs. 2 A to 2J. 

 Each point on these curves corresponds to a pair of values in Table I 

 except for the threshold values. The results of separate determina- 

 tions by the crew used in these loudness tests at different times are 

 given by the circles. The points represented by (*) are the values 

 adopted by Sivian and White. It will be seen that most of the 



20 40 



60 

 C 



100 120 20 40 



INTENSITY LEVEL-DB 



60 



D 



80 



100 120 



Fig. 2 (A to D) — Loudness levels of pure tones. 



