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Uncertainties associated with the use of a sound level meter.

Payne, R (2004) Uncertainties associated with the use of a sound level meter. NPL Report. DQL-AC 002

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Abstract

During the years from 1997 to 2001 the National Physical Laboratory provided a sound level meter verification service, where measurements of various parameters regarding the performance of a sound level meter were compared to the requirements of BS 7580. These measurements were carried out on a wide range of sound level meter types and the results are suitable for use in an assessment of a practical value of measurement uncertainties associated with the use of a sound level meter.
A value for measurement uncertainty associated with A-weighted noise emission levels, based on these verification data, together with contributions based on practical consideration of the operation and calibration of a sound level meter is proposed. This value is directly related to the practical use of sound level meters and should be suitable for inclusion in uncertainty budgets concerned with sound power level determination. In addition, the following simple guidelines regarding the practical use of a sound level meter are proposed.
To reduce the magnitude of measurement uncertainty resulting from the operation of a sound level meter, effort should be concentrated on reducing contributions associated with the time weighting and with indicator range changing. It is recommended that the indicator range used for measurements is the same as that used for the sound calibrator, and the slow time weighting is used. To reduce the magnitude of measurement uncertainty resulting from the use of a sound level meter, effort should be concentrated on reducing the effect of the observer. It is recommended that the indication on the sound level meter is observed remotely via an ac output (a common feature on class 1 meters).
The actual estimated value of measurement uncertainty assuming a slow time weighting is 0.39 dB. This value is reduced to 0.33 dB if there is no range change and there is no observer present. The reported combined total standard uncertainty for measurements carried out using the “slow” time weighting (with or without an observer and with or without a range change) is 0.4 dB.
For the majority of ISO sound power standards the frequency range of interest is specified as covering one-third octave bands centre frequencies from 100 Hz to 10 kHz. In this case the reported final total combined uncertainty associated with band limited noise emission is the same as the A-weighted value.

Item Type: Report/Guide (NPL Report)
NPL Report No.: DQL-AC 002
Subjects: Acoustics
Acoustics > Sound in Air
Last Modified: 02 Feb 2018 13:16
URI: http://eprintspublications.npl.co.uk/id/eprint/2976

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