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BELL SYSTEM TECHNICAL JOURNAL 



reference tone and a tone of different frequency, appeared equally 

 loud, then, making a similar comparison using one ear (the voltages 

 on the receiver remaining unchanged) he would still estimate that the 

 two tones were equally loud. The results upon which this conclusion 

 is based are shown in Table XVI. In the first row are shown the fre- 



TABLE XVI 



Comparison of One and Two-ear Loudness Balances 



A. Reference tone voltage level = — 32 db 



Frequency, c.p.s. 

 Voltage level 

 difference * 



10,000 

 -3.0 



B. Other reference tone levels 



* Differences are in db, positive values indicating a higher voltage for the one ear 

 balance. 



quencies of the tones tested. Under these frequencies are shown the 

 differences in db of the voltage levels on the receivers obtained when 

 listening by the two methods, the voltage level of the reference tone 

 being constant at 32 db down from 1 volt. Under the caption "Other 

 Reference Tone Levels" similar figures for frequencies of 62 c.p.s. and 

 2000 c.p.s. and for the levels of the reference tone indicated are given. 

 It will be seen that these differences are well within the observational 

 error. Consequently, the conclusion mentioned above seems to be 

 justified. This is an important conclusion and although the data are 

 confined to tests made with receivers on the ear it would be expected 

 that a similar relation would hold when the sounds are coming directly 

 to the ears from a free wave. 



This result is in agreement with the point of view adopted in de- 

 veloping the formula for calculating loudness. When listening with 

 one instead of two ears, the loudness of the reference tone and also 

 that of the tone being compared are reduced to one half. Conse- 

 quently, if they were equally loud when listening with two ears they 

 must be equally loud when listening with one ear. The second set of 



