Human Dimension of the Soundscape: From Individuals to Society - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 120

are exposed to a traffic noise level L Aeq, 24 h > 70 dB; this trend

is growing with time (Skanberg and Ohrstrom 2002 ; Ohrstrom et al. ( 2006 ).
Noise is considered in urban areas a real problem that is connected also to
topography, meteorology, land use patterns, and the lifestyle of the residents.
In residential areas, the soundscape shows variation in time and space connected
with the rhythms of the people. Buildings and artificial barriers create shields for
sound propagation that modify the sonic environment.
People locate the quiet areas that have a higher commercial value and concen-
trate their leisure time in open greenery spaces in which the noise level is lower:
30 % of variance associated with annoyance is linked to noise exposure. The weak
relationship between dose exposure and annoyance largely depends on the fact that
people move from one place to another and that noise exposure changes in space
and time.

55 dB and L Amax ¼

5.8 Consequences of Noise for Human Physiology
and Health

In humans the hearing mechanism is complex and has implications for different
organs (middle ear, acoustic nerve, cortex, and deep brain). Sound produces
reflexes in the muscular system and in the endocrine system also. Sound also elicits
also emotional reactions. Thus, the complexity of the acoustic performance depends
on several factors such as previous experience of the sounds, the simultaneous
presence of other environmental stimuli, the health status of the subject, etc.
(Rylander 2006 ).
The physiological reaction to different levels of sonic saturation reflects the
mechanism of the hormesis. Hormesis is defined as a dose response wherein a small
amount of the agent is beneficial and a large dose may have negative effects, and
this hormesis principle (Fig. 5.6 ) can be applied to the sonic ambience. People
relegated to an environment without acoustic stimuli, as in an anechoic chamber,
feel isolation and insecurity. People require a background of sounds to maintain
their physiological functions.
A sound is transformed into a noise after a subjective interpretation; definitively,
noise does not exist, but in some cases the mixing of different sounds creates a
white noise effect that does not allow distinguishing the component sounds. For
instance, a bird chorus at the maximum level during springtime prevents
distinguishing individual species and the sensation is of a diffuse “pleasant”
noise. Some types of music are considered unpleasant by some people and classified
as noise; for truck drivers, the sound of a truck engine can represent a familiar and
attractive sound while for other people this is just an unpleasant noise.
When exposed to a loud sound the subject tries instinctively to defend some parts
of the body with an involuntary contraction of the muscles around the eyes, in the
abdomen, and in the legs and the arms, preparing to escape subjecting the body to