Page 80 - The Master Handbook Of Acoustics

55
THE EAR AND THE PERCEPTION OF SOUND

useful up to a point, but it tells us little about human reaction to loud-
ness of sound. We need some sort of subjective unit of loudness. Many
experiments conducted with hundreds of subjects and many types of
sound have yielded a consensus that for a 10-dB increase in sound-
pressure level, the average person reports that loudness is doubled.
For a 10-dB decrease in sound level, subjective loudness is cut in half.
One researcher says this should be 6 dB, others say 10 dB, so work on
the problem continues. However, a unit of subjective loudness has
been adopted called the sone. One sone is defined as the loudness
experienced by a person listening to a tone of 40-phon loudness level.
A sound of 2 sones is twice as loud, and 0.5 sone half as loud.
Figure 3-9 shows a graph for translating sound-pressure levels to
loudness in sones. One point on the graph is the very definition of the

10

5

2
Loudness - sones 1

0.5
0.4
0.3

0.2

0.1
0 10 20 30 40 50 60 70

Loudness level - phons
FIGURE 3-9
The graphical relationship between the physical loudness level in phons and subjective loudness in sones.