Reference Document MCU22/0102 Updated Environmental Noise Assessment (2)

Terminology
Ambient Noise
Ambient noise refers to the level of noise from all sources, including background noise as well as
the source of interest.
A-Weighting
An A-weighted noise level is a noise level that has been filtered as to represent the way in which the
human ear distinguishes sound. This weighting indicates the human ear is more sensitive to higher
frequencies than lower frequencies. The A-weighted sound level is described as LA dB.
Background Noise
Background noise is the noise level from sources other than the source of interest. Background may
originate from such things as traffic noise, wind induced noise, industrial noise etc.
Decibel (dB)
The decibel is the unit that characterises the sound power levels and sound pressure of a noise
source. It is a logarithmic scale with regard to the threshold of hearing.
Impulsive Noise
An impulsive noise source is a short-term impact noise which may originate from such things as
banging, clunking or explosive sound.
LA1
An LA1 level is the A-weighted noise level which is overreached for one percent of a measurement
period. It represents the average of the maximum noise levels measured.
LA1 assigned level
An assigned LA1 level which is not to be exceeded for more than 1% of a delegated assessment
period.
LA10 assigned level
An assigned LA10 level which is not to be exceeded for more than 10% of a delegated assessment
period.
LA10
An LA10 level is the A-weighted noise level which is exceeded for 10 percent of the measurement
period and is considered to represent the “intrusive” noise level.
LA90
An LA90 level is the A-weighted noise level which is overreached for 90 percent of the measurement
period. It is represents the “background” noise level.
LAeq
LAeq refers to the comparable steady state of an A-weighted sound which, over a specified time
period, contains the same acoustic energy as the time-varying level during the specified time
period. It represents the “average” noise level.

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