Noise Mapping (Sound Level Modelling)

Noise has a multitude of effects on our environment and society. As part of modern civilizations standards and legal ruling have been developed and are continuously updated to set parameters for equipment limits, city, state or federal requirements. These standards and legal rulings regulate what is consider audible, acceptable, allowable or significant.

What is Noise ?

Noise is often defined as ‘sound which is undesired by the recipient’. A sound which one person finds enjoyable, such as some music perhaps, could be very annoying to another person who doesn’t want to hear it. Since it is quite probable that whatever the noise, there will be someone who doesn’t like it, there is a common presumption that all sound is bad. This presumption is even the basis of some legislation, which often seeks to limit sound levels on the basis that any sound could be annoying to someone. 

However, this presumption is by no means always true. Individual sensitivity to noise varies greatly and some people are not bothered by noise that would be intolerable to others. Moreover, there are many situations where noise is appropriate: for example a football match conducted in silence would be unnatural and hardly enjoyable for fans.

In English law, it is illegal to create noise which amounts to a nuisance, but in Common Law, the test is whether an ordinary person, taking account of the circumstances, would find the noise to interfere with the ‘enjoyment’ of their land to a material degree. Statute Law has changed the situation in recent years, and objective noise tests are becoming more important.

It is relatively easy to devise measurement units that can measure sound level, but because noise perception is subjective (ie it depends on the listener), acousticians have not been able to find a perfect unit or index for measuring noise.

This means that acousticians use a variety of measurement units that describe sound levels in a variety of ways. Using these as a guide to the impact of noise on people requires careful interpretation by skilled practitioners. 

However, increasing regulation, both national and European, is changing the situation, so that assessments are now more likely to depend on taking noise measurements in accordance with a defined procedure and for the result to be compared with objective guidelines.

What is noise mapping?

Sound modelling has become an increasingly popular tool in acoustics, often for assessing the impact of potential developments or for predicting the effects of noise mitigation methods. Using formulae for predicting the creation and propagation of sound that are provided in various standards and guidance and combining this with illustrative tools and visual aids it is possible to calculate and map out decibel levels, providing useful information that can help acoustic professionals.

A Noise Map is a map of an area which is coloured according to the noise levels in the area. Sometimes, the noise levels may be shown by contour lines which show the boundaries between different noise levels in an area.

The noise levels over an area will be varying all the time. For example, noise levels may rise as a vehicle approaches, and reduce again after it has passed. This would cause a short-term variations in noise level. In the slightly longer term, noise levels may be higher in peak periods when the roads are busy, and lower in off-peak periods. Then again, there is a greater volume of activity from more people and traffic in the day-time than in the evening or at night. In the longer term, wind, weather and season all affect noise levels.

This means that it is not possible to say with confidence what the noise level will be at any particular point at any instant in time, but where the noise sources are well-defined, such as road or rail traffic, or aircraft, then it is possible to say with some confidence what the long-term average noise level will be. 

It may be thought that the best way of doing this is by measurement, but experience shows that this is not the case. For a start, a long-term average must be measured over a long period of time. Secondly, to obtain complete coverage of an area, measurements would have to be made on private property, where access might be difficult, and thirdly, measurements cannot distinguish the different sources of noise, so they would not be able to give information on how much noise was being made by each of the sources in an area.

For these and other reasons, noise mapping is usually done by calculation based on a computerised noise model of an area, although measurements may be appropriate in some cases.

What is a noise model ?

A NoiseMap noise model supplies all the data that NoiseMap requires to undertake noise predictions.

At its simplest level, it can be regarded as a special form of digital map. The NoiseMap model must describe:

• Noise source, such as roads, vehicles, plant, railway tracks
• Transmission path, particularly noise barriers, ground topography and hard or soft ground cover
• Receiver locations

However, the user does not need to know in detail how these affect the generation and spread of noise. For example, a barrier may screen part of road from some receivers, but other receivers may not have any screening. The user does not need to consider this detail. You only have to make sure that you put into the model the various objects which affect the spread of noise, and NoiseMap will work out how these affect the noise level at any point of interest.

The noise model resembles the three-dimensional physical situation, but only includes the features which affect the spread of noise. These only need to be shown to a level of detail and accuracy which will give acceptable noise calculations.

A further benefit of having a noise model is that it can be used to assess the effects of transportation and other plans. Thus the effect of a proposed new road can be assessed and suitable noise mitigation can be designed to minimise its impact. This is particularly important in noise action planning, where a cost-benefit analysis of various options can be tested before a decision is made.

From modelling sound sources using real-world measured levels that are converted into sound power levels, or using sound power levels provided by manufacturers that have been taken in laboratory environments, it's possible to model the propagation of the noise generated by these objects in various scenarios. By taking traffic information or spot measurements and combining them with aerial views it is possible to map out the effects of an existing road on a hypothetical development, or predict the screening required to bring levels below the requirements given for minimising health effects.

European Noise Directive

The Environmental Noise Directive requires noise levels to be assessed from road traffic, railways, major airports and industry. It is not a requirement to assess noise generated by other activities, such as may arise from gardening, construction work, sports and leisure activities, pop concerts and the like.

Noise maps produced for the Environmental Noise Directive represent the annual average noise levels at a height of 4 metres above the local ground level.

The Environmental Noise Directive requires noise levels to be assessed in terms of Lden and Lnight.

Lden is the equivalent continuous noise level over a whole 24-hour period, but with noise in the evening (19:00 to 23:00) increased by 5 dB(A) and noise at night (23:00 to 07:00) increased by 10 dB(A) to reflect the greater noise-sensitivity of people at those times.

Lnight is the equivalent continuous noise level over the night-time period (23:00 to 07:00). Lnight does not contain any night-time noise weighting.

The UK government has published a procedure that allows LA10 (18-hour) levels to be converted into Lden and Lnight values. Because motorways carry a higher proportion of traffic at night compared with other roads, the conversion factors for motorways are different from the conversion factors for other roads.

UK Legislation

UK Legislation regulates most types of noise emission – whether from transportation, industrial, workplace, domestic or leisure sources. The legislation applies at many different levels – for example there are legal controls on the amount of noise most types of machinery can generate, including road vehicles and aircraft, construction plant and even some types of gardening equipment, such as lawnmowers. Together, there is now a huge volume of noise legislation and guidance. Some of this is given on our Links page.

There are also planning controls on the siting of noisy installations and also on the siting of noise-sensitive buildings, such as houses and schools. This means that when a new factory is planned, it must not cause undue noise at noise-sensitive premises, and also when new housing is planned, it must not be exposed to excessive noise.

New or improved roads are also subject to detailed noise assessment to ensure that they are planned and designed to take noise exposure into account. This work is complex and nowadays noise mapping is essential to the process.

Heavy investment is taking place to improve the UK railway network, with the introduction of faster trains providing a more frequent service. New rail links are also being planned or constructed, including extensions to the Docklands Light Railway and the proposed CrossRail link through Central London.

Again, noise mapping is being used to assess the potential not only for noise from the operational railway, but also from construction sites. These can be particularly problematic, as much railway construction work has to be done in ‘engineering hours’, ie when train services stop for the night.

When applying for planning permission for new housing, planning authorities require an assessment of the noise exposure, and again noise mapping is an ideal way of providing this information.

Equally, the noise exposure arising from new factories can easily be illustrated by noise maps. 

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Interested in our noise mapping services?

Our in-house Subject Matter Experts and design team uses below following softwares:

DataKustik's CadnaA environmental noise mapping software.

CadnaA offers a broad range of features for complex modelling scenarios and is widely used in the acoustics industry, including consideration of ground height, road prediction using CRTN and other object types such as foliage, railway and line/area sources.

SoundPLAN offers high end simulation software for noise modeling and air pollution calculations.

SoundPLAN Noise is following a standards based approach. With this software you can work in accordance to the regulations that apply in your area. SoundPLAN has implemented over 50 regulations for road noise, train noise, noise inside buildings, general industrial noise and aircraft noise. 

SoundPLAN understands itself as an advanced planning tool, not as a purely academic exercise, thus the program has a strong focus on what is needed to pinpoint the noise problems and suggest a path to fix them.

iFluids Engineering Noise Mapping / Sound Modelling Services

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