Methods - Soundscape Ecology: Principles, Patterns, Methods and Applications - page 237

9.7.1 Sound Pressure Measurements
Sound pressure measurements are largely used to assess the environmental “noise”
and represent an application to sound analysis largely devoted to industrial and
urban indoor and outdoor evaluation of the quality of the sonic environment These
measurements are required by law to be carried out by the Environment Protection
Policy on Noise. This approach is very popular for evaluating the effects of noise on
human life from different environmental conditions and is regulated by national and
international standards. Sound pressure measurement allows collecting the amount
of sound energy that is produced in a specific site at a precise instant or during a
time interval.
Here are reported a basic conceptual model of sound emission, propagation, and
potential annoyance as results from the Noise Measurement Procedures Manual
(2nd Edition, 2008; Environment Division, Department of Environment, Parks,
Heritage and the Arts, Australia).
• Acoustic energy is emitted from specific items of equipment or machinery.
• The energy radiation pattern can generally be approximated by assuming that all
sound energy from a particular item is emitted from a point source located at
about the centre of the item. Some variation to this may be necessary for
extended sources at close listening positions.
• The sound energy radiation pattern can generally be regarded as isotropic
(i.e. the energy radiates equally in all directions) unless there is evidence to
the contrary.
• The sound energy reduces with distance from the source in proportion to the
inverse square of the distance between the effective point source and any
listening position.
• The sound propagates through the air in relatively straight paths and can be
subjected to various modifications such as atmospheric absorption and refrac-
tion, which become increasingly more significant with increasing distance from
the source.
• The noise may be modified by the presence of sufficiently large objects that can
reflect, absorb or screen sound. This can lead to associated increases or decreases
in the sound pressure level at a particular listening position.
• Noise levels are measured with sound level meters that provide various signal
averaging and analysis options. The measurement results are normally displayed
in decibels (dB).
• The impact of environmental noise is likely to be greatest at locations where
humans are associated with noise sensitive situations. Thus noise levels are
generally reported in dB(A), which includes the A-weighting frequency
response that corresponds to the sensitivity of the human ear.
• The main concerns of environmental noise generally relate to interference of
such activities as sleep, relaxation, and conversation.