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The establishment of a rapid method of making sound power measurements of machinery noise emission.

Payne, R C; Simmons, D (1998) The establishment of a rapid method of making sound power measurements of machinery noise emission. NPL Report. CMAM 19

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This report examines in detail the methods described in the ISO 3740 and ISO 9614 series of standards with the principal aims of identifying an efficient standardized measurement technique to obtain rapid sound power measurements, with acceptable levels of measurement uncertainty, suitable for presentation of noise information in accordance with EC directives.
Sound power determinations have been carried out using 32 noise sources with Directivity Index (DI) ranging from 0.8 dB to 8 dB, in acoustic environments with values of K2A from zero to 9.6 dB. The effect on measured sound power levels and on measurement uncertainty of several factors including the number of measurement positions, measurement position orientation relative to source, area and type of enveloping surface, scan distribution and speed and the number of circular, spiral, meridional or rectangular paths, has been assessed. Results show that sound power level determinations performed in a wide range of acoustical environments when the number of measurements is significantly less than recommended in current international standards are of engineering grade accuracy for noise sources with a DI up to 4 dB and of survey-grade accuracy for noise sources with a DI of up to 8 dB.
It is concluded that the present series of standards describing methods for determining sound power levels of noise sources using sound pressure measurements is inadequate to meet present and foreseen regulatory requirements concerning the noise emission of machinery and equipment. The sub-division of standards into separate documents for different acoustic environments and different broad grades of accuracy raises unnecessary complications and makes it difficult for a user to interpret which standard is best suited to a particular application. A new series of standards is proposed, comprising only four documents, ultimately to replace all the existing ones. The measurement methods would relate the number of measurements of sound pressure level to the repeatability of the resultant sound power determination, allowing the number to be increased in order to achieve improved repeatability if required.

Item Type: Report/Guide (NPL Report)
NPL Report No.: CMAM 19
Subjects: Acoustics
Acoustics > Sound in Air
Last Modified: 10 Sep 2018 13:33
URI: http://eprintspublications.npl.co.uk/id/eprint/991

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