The Threshold of Audibility for Normal Person

Abstract

Measurements for determining the normal persons' threshold of audibility by air and bone conduction were made. For the calibration of sound pressure on the ear-piece (receiver), a similar apparatus to that of National Bureau of Standard's 9A Coupler was used here. All the threshold values in this paper are indicated by db unit with 0 db as one per sq. cm at each of the frequencies indicated below. The average threshold by air conduction for 50 normal ear per respective frequencies were as follows; -13. 0 at 125 c/s, -37. 2 at 250 c/s, -53. 3 at 500 c/s, -60. 8 at 1000 c/s, -60. 0 at 2000 c/s, -61. 5 at 4000 c/s, and -56. 3 at 8000 c/s. The threshold of audibility by bone conduction was measured in pressure by applying the bone conduction ear-piece (receiver) equipped with BaTio_3 ceramic element on the mastoid process. The values below represent the pressure in decibels with 0 db as one dyne. The average values for 30 normal ears were as follows: 22. 0 at 250 c/s, 18. 6 at 500 c/s, 3. 4 at 1000 c/s, -0. 7 at 2000 c/s and 11. 4 at 4000 c/s. "Normal ears" were defined in this paper as those having threshold values of within ±15db of the mean value in case of air conduction, and as those with threshold value of within ±20 db of the mean value in case of bone conduction.