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Assessment of reproducibility uncertainties for use in international standards on the determination of sound power.

Payne, R C; Simmons, D (2000) Assessment of reproducibility uncertainties for use in international standards on the determination of sound power. NPL Report. CMAM 51

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Abstract

A programme of inter-laboratory measurements designed to obtain estimates of the standard deviation of reproducibility associated with sound power level determinations has been carried out. These values of reproducibility uncertainty have been compared with values based on repeatability data, and uncertainty values suitable for inclusion in international standards are proposed. Four Laboratories carried out sound power level determinations using a hemispherical enveloping surface on three noise sources encompassing a wide range of acoustic complexity and covering a Directivity Index range from 0.8 dB to 6.9 dB. Sound power levels were determined using several microphone arrays with differing distribution on the enveloping surface and with between twenty and one measurement positions, and reproducibility uncertainties calculated for each array. The magnitude of reproducibility standard deviations is dependent on the number of microphone positions in the array, the Directivity Index of the noise source and the distribution of the microphone positions. For A-weighted sound power levels, a procedure is proposed that, for a given value of Directivity Index, will enable the user of a sound power standard to easily assess how many microphone positions are required in an array to obtain a required value of reproducibility, or, to assess the reduction in reproducibility that will be achieved by increasing the number of microphone positions. Standard deviations of reproducibility in a form suitable for inclusion in an international standard are proposed. For the purposes of an international standard it is suggested that a 10-microphone array should be specified when considering one-third octave-band sound power levels and that a value of reproducibility standard deviation of 1.5 dB across the frequency range from 50 Hz to 10 kHz should be adopted.

Item Type: Report/Guide (NPL Report)
NPL Report No.: CMAM 51
Subjects: Acoustics
Acoustics > Sound in Air
Last Modified: 02 Feb 2018 13:17
URI: http://eprintspublications.npl.co.uk/id/eprint/1546

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