- Introduction
- Maps and Tables
- Instructions
- Final Reports
- Glossary of Noise Terms
- Frequently Asked Questions
Glossary of Noise Terms
Decibel (dB): 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 (like a percentage).
Our sense of hearing is able to cope with a huge range of sounds.Humans can hear everything from the rustling of trees to a jet engine.In terms of power, the sound of the jet engine is about 1,000,000,000,000 times more powerful than the smallest audible sound.Decibels are useful because they allow such large ratios to be expressed as a convenient small number.
On the decibel scale the smallest audible sound (near total silence) is 0 dB. A sound 10 times more powerful is 10 dB. A sound 100 times more powerful than near total silence is 20 dB (see below for subjective evaluation of some different noise levels).
A-Weighted Decibel (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.
Sound is made up of different frequencies and because the ear is more sensitive to some frequencies than to others a weighting can be applied to simulate the response of the ear. The most common of these is the “A” weighting (dB(A)) and is frequently used in environmental noise measurements.Decibel (dB): 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 (like a percentage).
Our sense of hearing is able to cope with a huge range of sounds.Humans can hear everything from the rustling of trees to a jet engine.In terms of power, the sound of the jet engine is about 1,000,000,000,000 times more powerful than the smallest audible sound.Decibels are useful because they allow such large ratios to be expressed as a convenient small number.
On the decibel scale the smallest audible sound (near total silence) is 0 dB. A sound 10 times more powerful is 10 dB. A sound 100 times more powerful than near total silence is 20 dB (see below for subjective evaluation of some different noise levels).
A-Weighted Decibel (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.
Sound is made up of different frequencies and because the ear is more sensitive to some frequencies than to others a weighting can be applied to simulate the response of the ear. The most common of these is the “A” weighting (dB(A)) and is frequently used in environmental noise measurements.
Description |
|
| 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 an 8 hour period. |
| LAeq,16h | The A-weighted average sound level over the 16 hour period of 0700 – 2300 hours |
| 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. |
Noise Bands/Contours
Areas with similar noise exposure in 5 dB(A) ranges according to the key shown with the maps.
More formal definitions of some of the above terms can be found in the Environmental Noise Regulations (Northern Ireland) 2006.
Typical Noise Levels and Subjective Evaluation
| Noise Level dB(A) | Description |
120 |
Threshold of pain |
95 |
Pneumatic drill (un-silenced at 7m distance) |
83 |
Heavy diesel lorry (40 km/h at 7m distance) |
81 |
Modern twin-engine jet (at take-off at 152m distance) |
70 |
Passenger car (60 km/h at 7m distance) |
60 |
Office environment |
50 |
Ordinary conversation |
40 |
Library |
35 |
Quiet bedroom |
0 |
Threshold of hearing |