Page 76 - The Master Handbook Of Acoustics

51
THE EAR AND THE PERCEPTION OF SOUND

Loudness level-phons
120
120
110
100
100 90
Sound-pressure level - dB 80 80

70
60
60
50
40
40
30
20
20
10
Minimum
0
audible
20 50 100 300 1 kHz 3 kHz 10 kHz 20 kHz
Frequency - Hz
FIGURE 3-6
Equal-loudness contours of the human ear. These contours reveal the relative lack of sensitivity of the ear to
bass tones, especially at lower sound levels. Inverting these curves give the frequency response of the ear in
8
terms of loudness level. (After Robinson and Dadson. )

terms of loudness level. The ear is less sensitive to bass notes than
midband notes at low levels. There are wiggles in the ear’s high-
frequency response that are relatively less noticeable. This bass prob-
lem of the ear means that the quality of reproduced music depends on
the volume-control setting. Listening to background music at low levels
requires a different frequency response than listening at higher levels.

Loudness Control

Let us assume that the high fidelity enthusiast adjusts the volume con-
trol on his or her amplifier so that the level of recorded symphony
music is pleasing as a background to conversation (assumed to be