542 



BELL SYSTEM TECHNICAL JOURNAL 



99.5 

 99 

 98 



95 

 90 



< °° 

 O 60 



s ^° 



< 40 



Z 30 



^ 20 



(- 



(t '0 



S 2 



18 0-5 

 Q 0.2 



UJ 



0. eo 



a. 60 



"> 50 



fe 40 



H 30 



S 20 



10 

 5 



2 



I 

 0.5 



30 40 50 -20 -10 



HEARING LOSS IN DECIBELS 



Fig.' 



-Percentage of people In a given age and sex group having a hearing loss greater 

 than any given value. 



A hearing loss of 45 db for frequencies up to 1760 cycles will usually 

 make it difificult to hear direct conversation even when the speaker is 

 about two or three feet away. Individuals with this much loss usually 

 need some sort of hearing aid. Table 5 gives the percentages of 

 various groups that have losses in excess of 25 db and 45 db at the 

 various frequencies.^ 



Acuity for the two high-frequency tones is less important than for 

 the low tones for understanding speech, so that a loss for the high 

 tones is not such a serious handicap. High-tone deafness is of par- 

 ticular interest, however, to the extent that it is indicative of a pro- 



