Environmental noise levels are usually measured using professional sound level meters positioned at locations that represent the properties, development sites or other receptors being assessed.
However, a meaningful environmental noise survey involves much more than simply placing a meter on site and recording how loud the surroundings are.
The consultant needs to establish what type of noise is relevant, choose suitable monitoring positions, collect measurements during representative conditions and interpret several different acoustic indicators. Weather, operating periods and the character of individual sound sources can all affect the results.
For development projects, these measurements may help determine whether existing roads, industrial premises or other sources could affect a proposed noise-sensitive development. They can also be used to assess how industrial or commercial sound may affect existing neighbouring properties.
The objective is therefore not to find a single universal “noise level” for a site. It is to obtain representative data that answers the specific acoustic question relevant to the development.
What equipment is used to measure environmental noise?
Environmental noise surveys are carried out using specialist sound level meters.
For formal assessment work, the equipment needs to meet appropriate technical standards and be capable of recording the acoustic parameters required by the chosen assessment methodology.
For example, Environment Agency guidance concerning BS 4142 assessments specifies the use of an integrating-averaging sound level meter conforming to Class 1 requirements under BS EN 61672-1.
The microphone will normally be fitted with a windshield to reduce unwanted interference caused by air movement.
Depending on the assessment, equipment may remain in place unattended for an extended period or be operated by a consultant during attended measurements.
Unattended equipment can collect information over longer periods, allowing the consultant to understand how the acoustic environment changes throughout the day and night.
Attended measurements have a different advantage: the consultant can directly observe what is creating the sounds being measured.
In many assessments, a combination of recorded data and site observations provides the clearest understanding of the noise environment.
How is a sound level meter checked?
Acoustic measurement equipment needs to be checked to ensure that its readings remain reliable.
A field calibrator is normally used to check the sound level meter around the measurement period.
These checks help determine whether there has been any unexpected change or drift in the instrument.
Formal reports should also include appropriate information about the equipment and its calibration status.
For regulatory BS 4142 work, Environment Agency guidance requires valid calibration certificates and reporting of field calibration checks.
This quality control is important because small numerical differences can influence the interpretation of some types of noise assessment.
The consultant should therefore be able to demonstrate not only what was measured, but that suitable equipment and measurement procedures were used.
Is environmental noise measured in decibels?
Yes, environmental sound levels are expressed in decibels, usually written as dB.
However, simply saying that a site measured a particular number of decibels does not tell the full story.
Different acoustic indicators describe different aspects of the sound environment.
The most appropriate measurement depends on what is being assessed.
A consultant might need to understand the average sound level across a period, the background sound level during quieter moments or individual maximum events.
These indicators cannot necessarily be used interchangeably.
For example, the average sound environment beside a road may be useful for one type of assessment, while the quieter background level may be particularly important when assessing industrial or commercial sound.
Understanding these differences is one of the reasons professional interpretation is necessary.
What does LAeq mean?
One of the most commonly encountered measurements is LAeq,T.
Broadly, this represents the equivalent continuous A-weighted sound level over a specified period.
It allows a fluctuating acoustic environment to be expressed as a single representative level for that measurement period.
The “A-weighting” reflects the differing sensitivity of human hearing across frequencies.
The time period is also important.
A measurement taken over a short sample should not automatically be assumed to represent an entire daytime or night-time period unless there is evidence that the sample is representative.
For industrial and commercial noise assessment, current regulatory guidance specifically warns against measuring only during an unusually unfavourable period and treating that measurement as representative of the entire day or night.
The consultant therefore needs to understand how sound conditions change over time.
What does LA90 mean?
Another important acoustic indicator is LA90,T.
This represents the sound level exceeded for 90% of a specified measurement period and is commonly used to characterise the background sound environment.
In practical terms, it helps describe the underlying sound level rather than focusing on louder intermittent events.
This becomes particularly relevant when assessing industrial or commercial sound using BS 4142.
The relationship between the industrial sound and the existing background environment can help inform the assessment of its potential impact.
Background sound levels are not necessarily constant.
A location may have quite different conditions during weekday daytime periods, evenings and the middle of the night.
This is why the timing and duration of measurements need to reflect the operating periods and receptors being considered.
How are monitoring locations chosen?
Noise monitoring positions should be selected because they are representative of the assessment location, not simply because they are convenient places to install the equipment.
For a proposed residential development, this may mean monitoring in a position representative of future homes or outdoor spaces.
Where an existing industrial source is being assessed, monitoring may need to represent the residential properties most likely to be affected.
Distance from the sound source, intervening buildings, ground levels and screening can all influence the measured level.
Environment Agency guidance for BS 4142 measurements states that outdoor positions should provide results representative of the ambient and residual sound at the relevant assessment locations.
The consultant therefore needs to understand the relationship between the source, measurement position and receptor before the equipment is installed.
A measurement made in the wrong position may be technically precise but still provide poor evidence for the actual planning question.
How far should the microphone be from buildings?
Nearby surfaces can influence measured sound through reflections.
For that reason, microphone position relative to building facades and other reflecting surfaces needs to be considered when planning the survey.
Whether a measurement is intended to represent free-field conditions, facade conditions or another specific situation can affect both where the microphone is placed and how the result is interpreted.
The relevant methodology should therefore be established before monitoring begins.
This is another reason photographs, site plans and accurate measurement locations are important within an environmental noise report.
They allow the reviewer to understand where measurements were taken and how representative those locations are of the receptors being assessed.
Why does survey timing matter?
Environmental noise changes considerably throughout the day.
A road may be busiest during commuting periods.
An industrial operation may work only during daytime hours or could operate through the night.
A distribution facility might experience its greatest activity early in the morning.
Background conditions may become significantly quieter once traffic reduces in the evening.
The survey therefore needs to capture the periods relevant to the assessment.
There is little value in measuring an industrial site only while the relevant equipment is switched off if the purpose is to assess its normal operation.
Likewise, a short measurement during an unusually busy period may not accurately represent typical conditions.
The survey design should be based on an understanding of how the site and nearby sound sources actually operate.
Are daytime and night-time noise measured differently?
They may be considered separately because both the acoustic environment and people’s sensitivity to noise can change between daytime and night-time.
Background sound often reduces at night as road traffic and general activity decrease.
At the same time, noise affecting bedrooms can become particularly important because of the potential for sleep disturbance.
For developments containing residential accommodation, a noise survey may therefore need enough information to understand conditions across relevant daytime and night-time periods.
The precise assessment methodology depends on the sources and purpose of the study.
A road traffic noise assessment, for example, is not necessarily carried out or interpreted in the same way as an assessment of industrial sound.
The consultant needs to select the methodology relevant to the noise source and planning issue.
Why does the weather affect noise measurements?
Weather can influence both the sound being generated and how it travels between a source and receiver.
Wind can create unwanted noise directly across a microphone.
It can also affect vegetation and alter how sound propagates over distance.
Rain can significantly change the acoustic environment through sounds from wet road surfaces and rainfall itself.
For this reason, unsuitable weather conditions can make measurements unreliable or unrepresentative.
Environment Agency guidance for BS 4142 work requires weather conditions to be considered and reported, including wind speed and direction. It also states that specific, residual or background sound measurements should not be undertaken during or immediately after rainfall where those conditions would affect results.
Consultants therefore need to keep an eye on more than the sound level meter during a survey.
Meteorological conditions form part of understanding whether the measurements are valid.
What is attended noise monitoring?
Attended monitoring takes place while the consultant is present at the measurement position.
This allows them to identify which sound sources are audible and note events that could influence the readings.
For example, the consultant may observe that a measured increase was caused by a passing emergency vehicle rather than the industrial premises being assessed.
They may also identify tonal machinery, reversing alarms, intermittent impacts or other characteristics that cannot be fully understood from a numerical time history alone.
These observations can become particularly important in industrial noise work.
An environmental noise assessment is concerned not only with how loud something is but also, where relevant, with how the sound is perceived within its context.
Attended measurements can therefore provide valuable qualitative information alongside the measured data.
What is unattended noise monitoring?
Unattended monitoring involves leaving acoustic equipment operating at the site without a consultant remaining with it continuously.
This is useful where sound conditions need to be understood over longer periods.
The equipment can record how levels change throughout the survey, helping consultants identify differences between daytime, evening and night-time conditions.
Unattended monitoring can be particularly valuable where the environment varies substantially or where short attended measurements would not provide enough information.
However, longer monitoring does not automatically make an assessment better.
The survey period still needs to be representative, and consultants need enough contextual information to interpret what the equipment has recorded.
Audio recording, site observations and knowledge of nearby operations may sometimes assist with this process where appropriate.
How is industrial noise measured?
Industrial and commercial sound frequently requires a more detailed assessment than simply recording the overall ambient sound level.
BS 4142 is widely used in the UK for rating and assessing sound of an industrial or commercial nature. Current Environment Agency guidance identifies it as the relevant methodology for quantifying industrial and commercial noise impacts in its regulatory context.
The assessment may need to establish the sound associated specifically with the industrial activity as well as the underlying background environment.
This can sometimes be straightforward if the source can be switched on and off.
In other situations, separating the relevant source from surrounding sound may require additional measurements or calculations.
The character of the sound can also matter.
Tonality, impulsivity and intermittency may make a source more noticeable than its numerical level alone would suggest.
The consultant therefore considers both measured sound levels and relevant acoustic characteristics before reaching conclusions.
Are road traffic and industrial noise assessed in the same way?
No.
Although both involve environmental sound measurement, different noise sources can require different methodologies.
BS 4142 is specifically concerned with industrial and commercial sound and is not simply a universal method for assessing every form of environmental noise.
Environment Agency guidance, for example, explicitly distinguishes industrial or commercial sound within a site’s boundary from road traffic noise outside it.
For a development affected by several sources, the consultant therefore needs to determine which assessment methods are appropriate.
A site next to both a major road and an industrial facility may require consideration of both environments, but they should not necessarily be treated as though the same acoustic criteria apply to everything.
How are measurements turned into a noise assessment?
Collecting the measurements is only the fieldwork stage.
After the survey, the consultant reviews the data and considers it in the context of the relevant source, receptors and proposed development.
This may include identifying representative periods, analysing different acoustic indices and, where relevant, applying recognised assessment methodologies.
The consultant may also use calculations or computer modelling to predict how sound changes between the measurement position and proposed receptors.
For example, measurements taken at an existing industrial operation could contribute to calculations of expected noise levels at a future residential facade.
Where noise modelling or calculations are used, details such as site layout, source positions, receptors and proposed mitigation may need to be represented accurately. Regulatory guidance similarly requires clear information about the site, relevant sources and receptors when noise modelling forms part of an assessment.
The final report should explain how the measurements support the conclusions rather than simply presenting pages of acoustic data.
How can measured noise levels influence a development?
The results can have a direct influence on design.
If a proposed development is affected by significant road or industrial noise, the assessment may help determine which parts of the site are most exposed.
Architects can then consider matters such as building orientation, internal room layout, facade design and the positioning of outdoor amenity areas.
Where industrial noise is relevant, the findings can also help assess whether introducing noise-sensitive development could create a potential conflict with an established commercial use.
This information is considerably more useful when it is obtained before the design becomes fixed.
Developers can review Hawkins Environmental’s environmental services where environmental noise needs to be considered alongside other planning-related issues.
How long does an environmental noise survey take?
There is no single survey duration appropriate for every project.
The required period depends on the source, site and assessment objective.
Some sites may be characterised effectively using targeted attended measurements, while others require longer unattended monitoring covering daytime and night-time conditions.
Industrial sites may need measurements that coincide with representative operating periods.
A consultant should therefore determine the survey strategy from the actual environmental conditions rather than automatically using the same monitoring duration for every development.
A longer survey can provide more information, but representativeness is generally more important than duration alone.
Frequently Asked Questions
Can a phone app accurately measure environmental noise?
Mobile phone applications may provide a rough indication of sound levels, but they are not a substitute for appropriately specified and calibrated professional equipment where formal planning or environmental noise evidence is required.
Does a higher decibel reading always mean a more serious noise impact?
No. Overall level is important, but timing, duration, background conditions and the acoustic character of the source can also influence impact. Different assessment methodologies consider these factors in different ways.
Can an environmental noise survey be carried out before a development is built?
Yes. Noise surveys commonly measure the existing acoustic environment before construction. These measurements can then be used to determine how existing sources may affect the proposed development and inform its design.
Good noise measurement is about representative evidence
Environmental noise measurement involves far more than recording a decibel value.
A reliable survey requires suitable calibrated equipment, carefully selected monitoring locations, appropriate measurement periods and an understanding of the sources contributing to the acoustic environment.
Weather conditions, operating patterns and differences between daytime and night-time can all influence what the equipment records.
The measurements then need to be interpreted using the methodology appropriate to the particular source and planning question.
This is why the quality of an environmental noise assessment depends as much on survey design and professional interpretation as it does on the sound level meter itself.
For developers, architects and planning teams, the resulting information can provide an objective understanding of the existing noise environment and identify where acoustic considerations should influence a proposed development.
Hawkins Environmental carries out environmental noise surveys and assessments for development and planning projects. If noise from roads, industrial premises or other relevant sources could affect a proposed scheme, contact Hawkins Environmental to discuss the site and appropriate survey requirements.
Phone: 01256 522332
Email: enquiry@hawkinsenvironmental.co.uk
Find out more: hawkinsenvironmental.co.uk
