## Noise Mapping England

#### 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 this is frequently used in environmental noise measurements.

Because sound varies with time, as well as with frequency, it is necessary to determine suitable metrics/indicators to quantify and compare the sound. Some of the more commonly used metrics/indicators are listed below.

LAeq,T: The notional A-weighted equivalent continuous sound level which, if it occurred over the same time period, would have the same energy content as the actual varying sound level. The T denotes the time period over which the average is taken, for example LAeq,8h is the A-weighted 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.

LA10,T: The A-weighted level of sound exceeded for 10% of the measurement period (T)

LA90,T: The A-weighted level of sound exceeded for 90% of the measurement period (T)

LAmax: The A-weighted maximum level recorded during the measurement period.

##### Typical Noise Levels and Subjective Evaluation
 Noise Level dB(A) Description 120 Threshold of pain 95 Pneumatic drill (un-silenced at 7m distance) 94 Fast Train (180 km/h, behind yellow line on station platform) 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

The END and the corresponding Regulations refer to several noise indicators, including Lday, Levening, Lnight and Lden as well as other, supplementary noise indicators.

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.

More formal definitions of supplementary noise indicators can be found in the English Regulations 2006.

For the purposes of the END and the corresponding Regulations, the noise mapping results are based on an annual average 24 hour period.

Noise Bands/Contours: Noise bands are areas with similar noise exposure in 5 dB(A) ranges according to the key shown with the maps. Noise contours join locations with the same noise exposure.

#### Which Browsers are supported by this website?

The following browsers are supported by this website:

• Internet Explorer v6.x
• Internet Explorer v7.x
• Firefox v2.x

#### Why do I need to enable JavaScript?

JavaScript is required to get the optimum user experience from this site. In particular, by enabling JavaScript you will be provided with additional functionality to pan and zoom the map allowing you to navigate the noise data (otherwise with JavaScript disabled you will only be able to view the map at a set zoom level).

#### Why should I keep JavaScript disabled?

Some browsers are setup with JavaScript disabled by default (particularly under certain corporate security policies). This may prevent you from enabling JavaScript or could open up your computer to potentially harmful access. You do so at your own risk.

#### Internet Explorer v7.x & v6.x:

1. Go to the Tools menu and select Internet Options
2. In the Internet Options window, select the Security tab (at the top of the window)
3. Under the Security tab, select the Internet Web content zone
4. Under Security Level for this zone:
• If there is a slider bar move the slider bar to Medium.
• Otherwise, if the security level is Custom:
1. Click on the Custom Level button at the bottom of the page to open the Security Settings window
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5. Click OK

To disable JavaScript:

1. Click on the Custom Level button at the bottom of the page to open the Security Settings window
2. In the Security Settings window scroll down until you get to the section called Scripting (near the bottom)
3. Under Scripting there is a category Active scripting, select the option marked Disable for this category
4. Click the OK button

#### Firefox v2.x:

1. Go to the Tools menu and select Options
2. Select Content
3. Check enable JavaScript setting
4. Click OK

#### Why does the browser back button not work as expected?

It is recommended that you use the internal site navigation links at all times rather than the browser back button.

The browser back button will work inconsistently between different browsers (IE, Firefox, etc.) when using web applications such as the online Noise Mapping web viewer.

##### Why are there some gaps in the roads?

When viewing noise maps you may see 'gaps' in roads as seen in the image below. These occur when another unmapped feature such as a footpath or railway line passes over the road via a bridge or overpass and the road is not actually visible from above.

##### Why do some roads have white lines but no road surface?

As seen in the image above the road has no area but does have a white line. This occurs where the road travels under another unmapped feature (as described above) or where the road has not been designated as a public highway for that section.