Page 80 - Master Handbook of Acoustics

FIGURE 4-9 The graphical relationship between subjective loudness in sones and physical loudness
level in phons. This graph only applies to 1-kHz tones.

The idea of subjective loudness has great practical value. For example, a consultant might be
required by a court to give an opinion on the loudness of an industrial noise that bothers neighbors.
The consultant can make a 1/3-octave analysis of the noise, translate the sound-pressure levels of

each band to sones (using graphs such as Fig. 4-9), add together the sones of each band, and arrive at
an estimate of the loudness of the noise. It is convenient to be able to add component sones; adding
decibels of sound-pressure levels can be confusing.
Table 4-1 shows the relationship between loudness level in phons and the subjective loudness in
sones. Although most audio engineers have little use for phons or sones, it is good to realize that a
true subjective unit of loudness (sone) is related to loudness level (phon), which in turn is related by

definition to what we measure with a sound-level meter. There are empirical methods for calculating
the loudness of sound as perceived by humans from purely physical measurements of sound spectra,
such as those measured with a sound-level meter and an octave or 1/3-octave filter.