Noise Surveys and Their Different Types
What are the different types of Noise Survey and Noise Monitoring Services, and what are they for?
Noise Impact Assessment Noise Surveys
Noise Surveys are a common tool for Acoustic Consultants. The majority of projects undertaken by noise consultants will pretty much always rely upon a noise survey of some form.
Most commonly, a background noise survey is conducted. This is generally for use within a noise impact assessment to BS4142. Noise impact assessments to this British Standard follow a fairly simple formula. We look at the expected noise level of a proposed noise source and compare that to the existing background sound level. The background sound level in this case would be measured over a long period of time. This gives acoustic engineers an understanding of the noise levels over a period of days or weeks.
For noise impact assessments, BS4142 states that the noise survey should not to define the lowest sound levels in the local area. Rather it is used to define a typical background sound level. For example, BS4142 recommends that a noise survey is conducted with noise levels logged at 15-minute intervals. The defined background sound level is then calculated by taking the statistical mode over the noise survey duration.
Planning a Noise Survey
There are also other considerations which need to be made when planning a noise survey. Most often, the biggest challenge is the weather. This is not only to protect sensitive acoustic measurement equipment, but the weather will also affect the measured noise levels. For example, wet roads are much noisier than dry roads when vehicles are travelling along them. Similarly, high winds will cause high background noise levels and may also cause distortion to the acoustic measurement microphones. Generally, a noise survey should only be conducted in fine weather, with winds not exceeding 5 m/s.
We must also consider the microphone location when planning an acoustic survey. The microphones should always be placed in a location which is representative of the relevant noise sensitive receptor (most often a house). But we must also ensure that the location is not too close to and walls or reflecting surfaces, as this will increase the measured noise level (due to acoustic reflections). Where this cannot be avoided, corrections can be applied to counteract these reflections.
BS8233 & New Housing Developments
Similarly to noise impact assessments to BS4142, noise surveys are also required for new housing developments under BS8233. These two noise survey types are very similar, the main difference is in how the acoustic data is analysed. With BS4142, we are looking at background sound levels (LA90), whereas with BS8233 we are interested in the ambient sound level (LAeq) and Max levels (LAfMax). These acoustic measurement metrics can then be used in order to define appropriate glazing and ventilation specifications for the new housing development.
NCSL acoustic consultants also use noise surveys when event noise monitoring is required. Codes of practice exist for setting Music Noise Levels (MNL) from live music events, and in many cases this is based upon the existing background sound level. For example, for a monthly live music event the MNL should not exceed the background sound level by more than 15dB over a 15-minute period. This limit level would then be monitored by NCSL acoustic engineers during the duration of the event.
Planning Conditions
Another type of noise survey which is required are for industrial units which must adhere to planning conditions. In many cases, factories within residential areas will have planning conditions which require them to work within defined noise limits. A noise survey is generally conducted annually in order to ensure that the noise limits are being met. This minimises disruption to the client and the community.
Noise from Mining & Quarries
Heavy industry such as mining and quarrying are also subject to strict noise limits. This will generally require an annual noise survey at the nearest residential premises, ensuring the noise limits are not exceeded. If it is found that this is the case, then remedial action will be required in order to minimise the noise impact.
Vibration Surveys
If a development is close to a motorway or a railway, it may also be required to conduct a vibration survey. This is done to ensure that the estimated vibration levels within the proposed development are not exceeding the guideline values. This could subsequently be detrimental to the health of the residents.
Many different vibration measurement metrics are used, depending upon the use-case. Generally vibration is measured in three-axis and will usually be calculated as a dose value. This Vibration Dose Value (VDV) can be compared to the required levels and, where required, mitigation measures can be put in place.
If NCSL can be of service to you in terms of noise surveys, or acoustic consultancy services, then please contact us.