. Biophysical science. Biophysics. 12 Sound and the Ear /I : 3 exact sound pressure levels of the normal thresholds seem to be rather difficult to determine. The graph in Figure 5 shows the results of several investigations. These emphasize that the threshold depends to. I 0. 30cps 10 20 kc Frequency Figure 5. Pure tone thresholds. Note that the laboratory averages with trained, selected personnel are consistently lower than the mass survey averages. Recent studies at The Penn- sylvania State University by Professor J. Corso and his associ- ates gave mass survey values between the two cur
. Biophysical science. Biophysics. 12 Sound and the Ear /I : 3 exact sound pressure levels of the normal thresholds seem to be rather difficult to determine. The graph in Figure 5 shows the results of several investigations. These emphasize that the threshold depends to. I 0. 30cps 10 20 kc Frequency Figure 5. Pure tone thresholds. Note that the laboratory averages with trained, selected personnel are consistently lower than the mass survey averages. Recent studies at The Penn- sylvania State University by Professor J. Corso and his associ- ates gave mass survey values between the two curves shown. Notice that the threshold of feeling is not near the threshold of hearing at either 30 cps or 20 kc. The latter are limits of hearing in the sense that people can no longer distinguish tones outside of these limits. After J. G. R. Licklider, in Handbook of Experimental Psychology, S. S. Stevens, ed. (New York: John Wiley & Sons, Inc., 1951). some extent on who measures it. Notice that the ordinate is in decibels; thus a difference of 20 db means a factor of 10 in the sound pressure. All the curves show the same general shape with a minimum threshold, that is maximum sensitivity, in the frequency range from 1-4 kc. When the tests are conducted under controlled laboratory conditions, with carefully screened young people, the thresholds are lower than those found in mass surveys. There exist various types of limits of hearing, none of which are very precise. These limits include a minimum pressure threshold and an upper pressure limit at each frequency, as well as a highest and a lowest. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Ackerman, Eugene, 1920-. Englewood Cliffs, N. J. , Prentice-Hall
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