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BELL SYSTEM TECHNICAL JOURNAL 



loudness increases faster for the C sound for increments in the in- 

 tensity than for the A sound. For example, it is seen that when 

 the sound C is 30 units above the threshold, the sound A is 45 units 



o, „ R.M. 5. Pressure Arb. Units. 





100 800 1200 1600 £000 2100 



, R.M. 5. Pressure Arb. Units. Frequency 





mo 800 



50 



T3 



mo 



130 



*20 



%I0 



1200 1600 1000 2100 



Frequency 



10 20 30 40 50 



Units above threshold Sound C 



Fig. 5 



above the threshold when the two sound equally loud. In Fig. 6 

 a comparison is given between the loudness of a pure tone of 700 

 cycles and a complex sound designated by A in the last figure. In 

 this case again the relation is expressed by a curve. The technique 

 of making such loudness measurements is rather difficult and requires 

 a large number of observations before the values are reliable. A paper 

 on this subject which will soon be published will give a detailed account 

 of this work on loudness. 



Enough data have been given to show that in order to give loudness 

 a definite meaning for complex sounds, a more precise definition is 

 necessary. It has been found convenient to define the loudness of 

 any complex or pure tone in terms of the loudness of a sound standard. 



