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PEEQUENCT RANGE AND BEAEING PERCEPTION
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for a critical listener. Data were collected for more than 500,000 persons at the Telephone exhibit at the New Fork World's Fair in 1939 and 1940. The data were analyzed by Fletcher of the Bell Telephone Laboratories. The results of this analysis and related studies that are significant here are as follows.
At the intensity of 120 db (this is a very high near-pain intensity at the threshold of feeling) :
(1) The extreme range that can be perceived by a person with very acute hearing is about l»i to 22,000 eycles per second. Despite this extreme intensity, only about 5% of the population can perceive this range.
The median range that can he perceived by a person with average hearing is about 20 to 15.000 cycles per second at this intensity. Xote that this range is shortened at both ends when compared with condition (1).
(3) The narrow range that is perceived by the 5% of the population with the poorest hearing is less than 2~> to 7,000 cycles per second at this intensity. Xote that this range is further shortened at both ends when compared with conditions (2) and
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Fig. 27. Hearing contours for average (median population) and critical (5% most acute) listeners in absence of noise.
When the intensity is reduced from the extreme intensity of 120 db to the more customary intensity ranges used in reproducing 16-mm sound films (55 to 75 db), all thra groups suffer a further hearing loss at both
i nds of the spt drum. For comparison purposes it may be mentioned thai 55 db represents the lowest intensity customarily used in the home with