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BELL SYSTEM TECHNICAL JOURNAL 



From these loudness level contours, the curves shown in Figs. 5A 

 and 5B were obtained. They show the loudness level vs. intensity 

 level with frequency as a parameter. They are convenient to use for 

 calculation purposes. 



It is interesting to note that through a large part of the practical 

 range for tones of frequencies from 300 c.p.s. to 4000 c.p.s. the loudness 

 level is approximately equal to the intensity level. From these curves, 

 it is possible to obtain any value of Lk in terms of ^k and fk. 



100 500 1000 



FREQUENCY IN CYCLES PER SECOND 



Fig. 4. — Loudness level contours. 



6000 



On Fig. 4 the 120-db loudness level contour has been marked 

 "Feeling." The data published by R. R. Riesz ^ on the threshold of 

 feeling indicate that this contour is very close to the feeling point 

 throughout the frequency range where data have been taken. 



Determination of the Loudness Function G 



In the section " Formulation of the Empirical Theory for Calculating 

 the Loudness of a Steady Complex Tone," the fundamental equation 

 for calculating the loudness level of a complex tone was derived, 



" R. R. Riesz, "The Relationship Between Loudness and the Minimum Perceptible 

 Increment of Intensity," Jour. Aeons. Soc. Am. 4, 211 (193vS). 



