ARCHIVE: Noise mapping glossary

Decibel (dB)
The decibel (dB) is a logarithmic unit of measurement that expresses the magnitude of a physical quantity relative to a specified or implied reference level. Its logarithmic nature allows very large or very small ratios to be represented by a convenient number. Being a ratio, it is a dimensionless unit. Decibels are used for a wide variety of measurements including acoustics, and for audible sound A-weighted decibels (dBA) are commonly used.
dB(A)
A unit of sound pressure level, adjusted in accordance with the A weighting scale, which takes into account the increased sensitivity of the human ear at some frequencies
LAeq,T
The notional A-weighted equivalent continuous sound level which, if it occurred over the same time period, would give the same noise level as the actual varying sound level.  The T denotes the time period over which the average is taken, for example LAeq,8h is the equivalent continuous noise level over a 8 hour period.
Lday
The A-weighted average sound level over the 12 hour day period of 0700 – 1900 hours.
Levening
The A-weighted average sound level over the 4 hour evening period of 1900 – 2300 hours.
Lnight
The A-weighted average sound level over the 8 hour night period of 2300 – 0700 hours.
Lden
The day, evening, night level, Lden is a logarithmic composite of the Lday, Levening, and Lnight levels but with 5 dB(A) being added to the Levening value and 10 dB(A) being added to the Lnight value
LAeq,16h
The A-weighted average sound level over the 16 hour period of 0700 - 2300
Noise Bands
Areas with similar noise exposure in 5 dB(A) ranges according to the key shown with the maps
Noise Contours
Lines showing the locations with the same noise exposure according to the key shown with the maps.
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Page last modified: 16 May 2008

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