PROCEEDINGS 
OF THE 
NATIONAL ACADEMY OF SCIENCES 
Volume 7 AUGUST 15, 1921 Number 8 
SOME PHYSICAL CHARACTERISTICS OF THE EAR 1 
By John P. Minton 
Ryerson Physical Laboratory, University of Chicago 
Communicated by R. A. Millikan, June 3, 1921 
By means of the audion oscillator, a special telephone receiver tuned 
to a high natural period and placed against the ear and a suitable circuit 
numerous tests at various frequencies have been made on the minimum 
audibility current for both normal and abnormal ears. From these data 
important conclusions can be drawn regarding the physical and physiologi- 
cal structure of the ear and also concerning the functioning of the ear and 
the auditory nerves with their endings as organs of hearing. The con- 
clusions drawn, then, are based on precise physical measurements which 
can be checked to within about five per cent from time to time. 
Sensitivity of Normal Ears. — Ears are considered normal when no physi- 
ological defects are observable by the otologist. If we define sensitivity 
as the reciprocal of the minimum vibrational energy in ergs of the receiver 
diaphragm that the normal ear can detect, then curves can be plotted show- 
ing the sensitivity as a function of the frequency. This has been done for a 
number of normal ears. The curve shown in figure 1 is a typical one. It is 
to be observed that up to about 6000 cycles three distinct maxima of sensi- 
tivity are present; one at 900 cycles, one 1800 and another one at 3900. 
It is also important to observe that the sensitivity is much greater through- 
out the region from 200 to 4500 cycles than outside this range. Within 
this region are included all the frequencies which are of most importance 
for both speech and music. The natural period of the receiver was 5215 
cycles when this curve was taken and the absence of a peak in this position 
shows that the receiver characteristics have been corrected for satisfactorily. 
All the maxima, then, occur below the resonant frequency of the receiver. 
Curves on other normal ears show maxima which agree for the most 
part in location but not in magnitude with the curve shown in figure 1. 
Because of the marked similarity between the response curves for coupled 
mechanical vibratory systems and the curves for normal ears, it seems 
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