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|
The
human ear is sensitive to sound waves with frequencies in the
range from a few hertz to almost 20 kHz. The intensity of a
sound is measured in terms of sound pressure level, an
acoustic scale independent of frequency, expressed in decibels
(dB), where 0 dB (the threshold of hearing) corresponds to
sound pressure level of 20 µPa, the minimum detectable 1000
Hz sound pressure level by average human ear.
The
subjective auditory response is frequency dependent and it is
measured in terms of loudness level of a sound, for which two
units of measurement are used: phon and sone. Phon
is defined as loudness of 1000 Hz sound at the sound pressure
level of 20 µPa. Loudness level of a sound, expressed in phons,
is numerically equal to the sound pressure level, expressed in
decibels, of the 1000 Hz sound judged by listeners to
be equivalent in loudness. The threshold of hearing is also
frequency dependent and an acoustic scale which relates
loudness to a threshold of a particular listener is expressed
in sones; sone is defined as loudness of 1000 Hz
sound, 40 dB above a listener’s threshold. Loudness level of
a sound, expressed in sones, measures a loudness level
above threshold for a particular listener; for that reason,
the threshold (measured or assumed) should be always
specified.
|
loudness
level as a function of sound pressure level (SPL)
and
frequency / phon |
| SPL |
frequency
/ Hz |
| dB |
125 |
250 |
500 |
1,000 |
2,000 |
4,000 |
8,000 |
10,000 |
| 10 |
|
|
|
10.0 |
18.0 |
18.0 |
|
|
| 20 |
|
6.3 |
16.0 |
20.0 |
28.0 |
28.0 |
11.0 |
|
| 30 |
4.0 |
18.0 |
26.5 |
30.0 |
37.0 |
36.5 |
20.5 |
17.0 |
| 40 |
17.0 |
31.0 |
38.5 |
40.0 |
45.5 |
45.0 |
29.5 |
26.0 |
| 50 |
34.0 |
45.5 |
52.0 |
50.0 |
55.0 |
54.0 |
38.0 |
35.0 |
| 60 |
52.0 |
59.5 |
64.5 |
60.0 |
64.0 |
63.5 |
47.0 |
43.5 |
| 70 |
70.0 |
72.5 |
76.0 |
70.0 |
73.5 |
72.5 |
56.0 |
43.5 |
| 80 |
86.0 |
84.5 |
86.0 |
80.0 |
84.5 |
83.0 |
66.0 |
63.5 |
| 90 |
98.0 |
95.5 |
96.0 |
90.0 |
95.0 |
94.5 |
77.0 |
73.5 |
| 100 |
108.0 |
105.5 |
105.0 |
100.0 |
106.0 |
106.0 |
88.0 |
85.5 |
| 110 |
118.0 |
115.5 |
113.0 |
110.0 |
117.0 |
117.5 |
101.5 |
98.0 |
|
|
| |
20
frequency bands contributing equally
to
efficiency of speech communications |
|
| |
band |
frequency
range |
|
band |
frequency
range |
|
band |
frequency
range |
|
| |
# |
Hz |
|
# |
Hz |
|
# |
Hz |
|
| |
1 |
395 |
|
8 |
1,250 - 1,425 |
|
15 |
2,930 - 3,285 |
|
| |
2 |
395 - 540 |
|
9 |
1,425 - 1,620 |
|
16 |
3,285 - 3,700 |
|
| |
3 |
540 - 675 |
|
10 |
1,620 - 1,735 |
|
17 |
3,700 - 4,200 |
|
| |
4 |
675 - 810 |
|
11 |
1,735 - 2,075 |
|
18 |
4,200 - 4,845 |
|
| |
5 |
810 - 950 |
|
12 |
2,075 - 2,335 |
|
19 |
4,845 - 5,790 |
|
| |
6 |
950 - 1,095 |
|
13 |
2,335 - 2,620 |
|
20 |
5,790 |
|
| |
7 |
1,095 - 1,250 |
|
14 |
2,620 - 2,930 |
|
|
|
|
| |
loudness
threshold as a function of age and frequency
decibels
to be added for an age group |
|
| |
age group |
frequency
/ Hz |
|
| |
125-1,000 |
2,000 |
4,000 |
6,000 |
8,000 |
10,000 |
|
| |
woman 30-39 |
1 |
2 |
3 |
4 |
4 |
4 |
|
| |
woman 40-49 |
3 |
5 |
6 |
8 |
9 |
9 |
|
| |
woman 50-59 |
5 |
9 |
13 |
18 |
20 |
22 |
|
| |
man 30-39 |
1 |
2 |
5 |
6 |
6 |
7 |
|
| |
man 40-49 |
2 |
5 |
13 |
13 |
11 |
13 |
|
| |
man 50-59 |
5 |
13 |
27 |
32 |
35 |
35 |
|
|
|
|
|
Source: Speech
and Hearing, by E.D. Newman, in American Institute of Physics
Handbook (D.E. Gray, Ed.), Chap. 3, McGraw Hill, New York, 1972.
[R19] |
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