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Measurement uncertainties associated with sound power level determination due to source operating conditions.

Jobling, B; Simmons, D; Payne, R (2004) Measurement uncertainties associated with sound power level determination due to source operating conditions. NPL Report. DQL-AC 006

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Manufacturers can demonstrate compliance with regulations by carrying out measurements in accordance with internationally standardised methods. The machinery industry commonly refer to the ISO 3740 series of standards, which specify various methods for determining sound power levels of machines, equipment and their assemblies over a measurement surface enveloping the source, within different environments. This series of standards is currently under short-term revision, and high on the agenda is the introduction of full uncertainty budgets consistent with the ISO “Guide to the expression of uncertainty in measurement”. The implications of having this information are important, where uncertainty values are used in practice to derive the final guaranteed sound power level, which is used as an absolute indicator on noise labels affixed to machines.
The effect of noise source operating conditions on the determination of sound power level needs to be accounted for in the ISO 3740 uncertainty budgets. However, the discrete effect of operating conditions on the overall measurement uncertainty is unknown. An investigation has been conducted involving an extensive series of sound power determinations for a range of machinery, primarily with internal combustion-engine power sources, enabling evaluation of repeatability uncertainties. The mean standard uncertainty for machines with a continuous steady noise output obtained from analysis of a range of sources was found to be 0.2 dB. Using a dataset of standard deviations of repeatability determined for machines tested with an activity type operation, the mean standard uncertainty was found to be 1.0 dB.

Item Type: Report/Guide (NPL Report)
NPL Report No.: DQL-AC 006
Keywords: source conditions
Subjects: Acoustics
Acoustics > Sound in Air
Last Modified: 02 Feb 2018 13:16
URI: http://eprintspublications.npl.co.uk/id/eprint/3024

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