Machinery Noise Guide: Short term revision of the standards
Short-term revision of the ISO basic series
The ISO sound power standards are currently undergoing short-term revision, coordinated by ISO committee ISO/TC43/SC1/WG28. In fact two successive revisions are envisaged, one in the short term based on existing knowledge, and a further more radical one in the longer term, assuming extra research is conducted.
Objectives of revision of the 3740 series
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to edit the standards so as to unify the structures, terminology, and definitions, and treatment of common aspects, across the standards
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to add clauses to those standards which do not already have them, covering determination of the sound energy level for noise sources emitting bursts of sound
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to unify the treatment of measurement uncertainties in all the standards and add guidance showing how the uncertainties can be expressed in a manner consistent with the ISO Guide to the expression of Uncertainties in measurements (GUM)
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to provide the information necessary to allow determination of the sound power levels and energy levels under reference meteorological conditions, For engineering and survey grade methods
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to extend the range of acoustical environments in which ISO 3744 may be applied (k2 extended to 4 dB)
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to incorporate relevant aspects of ISO 4872 into ISO 3744 and so make possible the withdraw of ISO 4872
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to remove ISO 3745 Annex A giving general procedures for qualifying free-field (and Hemi-anechoic) rooms.
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to introduce cylindrical and mixed measurement surfaces in ISO 3744
The target date for the short term revision is 2006.
Objectives of revision of ISO 9614 series
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to edit the standards so as to unify their terminology and definitions with those of the ISO '3740' series
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to unify the definitions and methods of applying the indicators through the three parts of the series
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to unify the treatment of absorption within the measurement surface and of the impact of air flow throughout the series
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to unify the treatment of measurement uncertainties with that being developed for the ISO 3740 series and add guidance showing how the uncertainties can be expressed in a manor consistent with the ISO Guide to the expression of uncertainties in measurements (GUM)
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to provide the information necessary to allow determination of the sound power levels and energy levels under reference meteorological conditions, For precision and engineering grade methods
Formal discussions to revise ISO 9614 have yet to be taken but these can be expected during 2005 with target dates to complete them three years later.
Summary of significant changes applying to the whole series
Editorial Changes
Disparity in the organisation of the series has resulted in information on similar or related issues dispersed in separate clauses. This can make it over-complicated for a user to interpret the standard. To address this disparity editing has brought together related terms to reduce the need to refer back and forth through the document. These editorial actions have been carried through the whole series to provide a more unified structure.
Uncertainty Budgets
One of the most important changes to the standards is the introduction of full uncertainty budgets consistent with the ISO Guide to the expression of uncertainty in measurement (GUM). The current ISO basic series does not provide information on the analysis of measurement uncertainty components, and their magnitudes.
The accepted format for expressing uncertainties is given in the GUM. The format includes an uncertainty budget, in which the various sources of uncertainty are identified and quantified, from which a combined uncertainty is derived. The uncertainty budgets will be in an informative Annex but the intention is that in the future it will replace the reproducibility uncertainty, which is quoted currently in the standards.
Sound Energy
For a noise source that emits sound in a sudden burst, the noise emitted has to be evaluated by the total sound energy rather than the sound power. The sound energy level for transient noise emission is then derived by calculation from the single-event sound pressure levels in the space surrounding the noise source, in ways similar to those based upon the time-averaged sound pressure levels of a source emitting continuous noise to obtain the sound power level.