Attachment 4 - Existing_Acoustic_Environment (22.01.20)

3     NOISE TARGETS

3.1    ACOUSTIC DESCRIPTORS

Environmental noise constantly varies. Accordingly, it is not possible to accurately determine prevailing
environmental noise conditions by measuring a single, instantaneous noise level.

To accurately determine the environmental noise a 15-20 minute measurement interval is utilised. Over this
period, noise levels are monitored on a continuous basis and statistical and integrating techniques are used
to determine noise description parameters.

In analysing environmental noise, three-principle measurement parameters are used, namely L10, L90 and Leq.

The L10 and L90 measurement parameters are statistical levels that represent the average level generally used
to determine traffic/entertainment noise and average minimum noise levels respectively, over the
measurement intervals.

The L10 parameter is commonly used to measure noise produced by a particular intrusive noise source since
it represents the average of the loudest noise levels produced by the source.

Conversely, the L90 level (which is commonly referred to as the background noise level) represents the noise
level heard in the quieter periods during a measurement interval. The L90 parameter is used to set the
allowable noise level for new, potentially intrusive noise sources since the disturbance caused by the new
source will depend on how audible it is above the pre-existing noise environment, particularly during quiet
periods, as represented by the L90 level.

The Leq parameter represents the average noise energy during a measurement period. This parameter is
derived by integrating the noise levels measured over the 15 minute period. Leq is important in the
assessment of traffic noise impact as it closely corresponds with human perception of a changing noise
environment; such is the character of environmental noise.




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