NMS Project 2.2
NMS Project 2.2
Project Team
Key Technical Issues
Documents
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NMS Project 2.2
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UK NMS Programme
NMS Project 2.2
Project Team
Key Technical Issues
Documents
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This is the project website of Project 2.2 ‘Environmental Noise’ of the Department of Trade and Industry’s National Measurement System Acoustical Metrology Programme. The project has been let under Theme 2 ‘Standards for Noise & Vibration’ of the NMS Programme.
The overall aims of the project are to:
In order to achieve the foregoing aims, the specific objectives of NMS Project 2.2 comprise:
Under real life field conditions the quality and face validity of environmental noise measurements can be subject to considerable uncertainty. Some of the uncertainties arise from unavoidable variation in accuracy and calibration of the instrumentation used. However, the ‘technical uncertainty’ which results from such variations is often small when compared with the ‘procedural uncertainty’ that may arise from adopting different approaches to measuring noise.
Estimates of noise environments are, for example, often based on short term sampling of the sound field at fixed locations. In contrast, many noise environments vary considerably over both space and over time. The precise timing and location of any noise measurement can therefore significantly influence the measured noise level.
The introduction of these potential variations in measured noise level results in a ‘procedural uncertainty’ that is then associated with the result level. Procedural uncertainty may apply equally to the measurement of background noise as to the measurement of the specific noise associated with a given source of noise.
It is a major objective of the present project to provide guidance on how procedural uncertainty in the measurement of both background and specific environmental noise may be understood and reduced. This will be achieved via a study of existing data, and also through the measurement of new environmental noise data in specific situations. The ultimate outcome of the project is to produce formal guidance on the measurement of environmental noise. This guidance will supplement that produced by Salford University under a previous NMS contract. That contract resulted in the publication of the guidance document ‘A good practice guide on the sources and magnitude of uncertainties arising in the practical measurement of environmental noise’, University of Salford, October 2001.
The Salford guide presents means for estimating the cumulative uncertainties as they exist in the measurement of environmental noise. The programme of work to be undertaken under the present Project 2.2 extends the Salford work to identify means of reducing uncertainties within realistic practical and cost effective constraints.
The second part of present Project 2.2 concerns the evaluation of presently available methodologies for the identification and classification of acoustic features in environmental noise. Environmental noise measurements are made for a range of purposes: for planning, for assessing complaints, and for assessing baselines. The key issue is that any measurement must be meaningful in terms of the relationship of the measured parameters to subjective response. The aim of the NMS programme is to maintain an infrastructure to ensure that measurements in the UK are valid, fit for purpose, and consistent. The infrastructure exists to promote the UK’s economic competitiveness and therefore should be fair.
Any noise assessment method should:
The development of future standards and this proposed work must therefore take these requirements into account.
Previous DoE work showed that the existing standard such as BS 4142 and ISO 1996 did not adequately meet the requirements set out above, despite the fact that a recent study revealed over 50% of real world environmental noise problems in the UK result from the presence of acoustic features within the offending noise. In fact the work led to the development of a new approach to practical noise control based on controlling acoustic features, rather than focusing on overall noise energy (see Porter, Flindell, Berry, An acoustic feature model for the assessment of environmental noise, Acoustics Bulletin, IOA, Nov/Dec 1993). This approach took more account of the complexity of the subjective response to noise and the above requirements. The new approach suggested that each feature should be examined separately, and one outcome was that the team ‘acoustic feature’ was introduced into the text of BS 4142.
All three work elements of the Project will use as their starting point an extensive literature survey of the state of the art in the areas of acoustic feature identification, measurement of background noise and measurement of specific noise associated with industrial/commercial sources. The literature search will extend beyond the UK to EU member states and other countries worldwide.
The literature search will be supplemented by direct contact with acknowledged experts in the respective fields, together with the distribution of questionnaires to evaluate current practices followed by consultants, environmental health officers and other environmental noise measurement practitioners in the UK.
Based on the feedback from the consulted experts and the questionnaire surveys, and also based on the analysis of existing environmental noise data available to the project team, real-world situations will be identified in which the uncertainties in the measured level of both background and specific noise can be reduced. Draft guidance will be produced on minimizing the uncertainties in these instances. Project specific, dedicated noise measurements will then be undertaken to confirm and illustrate the draft guidance.
The main deliverable of the project will be a written ‘Guide to Environmental Noise Measurement’ which will be based on comprehensive reviews of specific user requirements, the results of recent and ongoing international research and a comprehensive inter-comparison of alternative measurement procedures taking both technical and procedural uncertainties into account, looking at both background noise and specific noise separately.
A second report will be produced that will consider the objective identification of acoustic features. This report will assimilate existing published data on the subject, and will further report on the application of existing methodologies to sample recordings of specific noise.
A key innovation will be the separate consideration of both technical and procedural uncertainties and how these can be reduced by careful attention to the detailed design of environmental noise measurement surveys based on a prior consideration of how the results of any surveys will be used for practical assessment purposes. The published guide will strike an appropriate balance between the fundamental requirement to maintain an approach to the design of noise measurement surveys based on informed flexibility, while also providing a sufficient degree of prescriptive guidance that the large range of procedural uncertainties which exist at present can be significantly diminished. The optimum balance between flexibility and prescribed approaches can only be reached in the light of a more detailed understanding of precise user requirements elaborated in terms of possible outcome measures.
A separate innovation will be the use of a dedicated web-site for increasing the scope and breadth of consultation and for ongoing dissemination of preliminary and final results. The web-site may include measurement algorithms and practical examples for demonstration purposes, depending on requirements as identified via user consultations.
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