Page 81 - The Master Handbook Of Acoustics

56 CHAPTER THREE

sone, the loudness experienced by a person hearing a 1,000-Hz tone at
40-dB sound-pressure level, or 40 phons. A loudness of 2 sones is then
10 dB higher; a loudness of 0.5 sones is 10 dB lower. A straight line can
be drawn through these three points, which can then be extrapolated
for sounds of higher and lower loudness.
As crude as this graph may be, it is a way of getting at the subjec-
tive factor of loudness. The value of this line of reasoning is that if a
consultant is required by a court to give his or her opinion on the loud-
ness of an industrial noise that bothers neighbors, he or she can make
a one-third octave analysis of the noise, translate the sound-pressure
levels of each band to sones by the help of a series of graphs such as
Fig. 3-9, and by adding together the sones of each band, arrive at an
estimate of the loudness of the noise. This idea of being able to add
component sones is very nice; adding decibels of sound-pressure lev-
els is a path that leads only to confusion.
Table 3-1 shows the relationship between loudness level in phons
to the subjective loudness in sones. Although most audio workers will
have little occasion to become involved in phons or sones, it is good to
realize that a true subjective unit of loudness (sone) is related to loud-
ness level (phon), which is in turn related by definition to what we can
measure with a sound-level meter. There are highly developed empir-
ical methods of calculating the loudness of sound as they would be
perceived by humans from purely physical measurements of sound
spectra, such as those measured with a sound-level meter and an
octave or one-third octave filter. 10

Table 3-1. Loudness level in phons vs. Loudness and Bandwidth
loudness in sones.
In the discussion of loudness we have
Loudness Subjective
talked tones up to this point, but single-
level loudness
frequency tones do not give all the informa-
(phons) (sones) Typical examples
tion we need to relate subjective loudness
100 64 Heavy truck passing to meter readings. The noise of a jet aircraft
80 16 Talking loudly taking off sounds much louder than a tone
60 4 Talking softly
of the same sound-pressure level. The
40 1 Quiet room
bandwidth of the noise affects the loudness
20 0.25 Very quiet studio
of the sound, at least within certain limits.