Sound power level and emission sound pressure level of machines

Status:

completed 06/1999

Aims:

The Machinery Directive 98/392/EEC calls upon the manufacturers of machinery to provide information on the sound emission of their machines. To determine the sound emission characteristics of machines, new measurement methods were developed and described in EN ISO standards. For the determination of the emission sound pressure level alone, five different measuring methods are available. As these standards had been tested and practically applied by only a few institutes, a project was conducted, with financial support from the European Commission, in the context of which the measurement methods were tested and optimised for different machines and under varying framework conditions. Particular attention was paid to the problem of measurement uncertainties and to the classification of the methods on account of precision classes.

Activities/Methods:

Comparative measurements were conducted by a total of 17 European test houses. The investigations under real operating conditions included six differently sized machines. The comparison method according to EN ISO 3747 "Acoustics - Determination of sound power levels of noise sources using sound pressure - Comparison method for use in situ" was used to determine the sound power level; the results were compared to those of the proven sound intensity method according to EN ISO 9614-2 "Acoustics - Determination of sound power levels of noise sources using sound intensity - Part 2: Measurement by scanning" and - as far as possible - to the reverberation room method in accordance with EN ISO 3741 "Acoustics - Determination of sound power levels of noise sources using sound pressure - Precision methods for reverberation rooms". The emission sound pressure level at the workplace was determined both in the framework of a sound pressure measurement according to EN ISO 11201 "Acoustics - Noise emitted by machinery and equipment - Measurement of emission sound pressure levels at a work station and at other specified positions - Engineering method in an essentially free field over a reflecting plane, EN ISO 11202 "Survey method in situ", EN ISO 11204 "Method requiring environmental corrections" and in the context of a sound intensity measurement as described in the draft paper ISO 11205 "Acoustics - Determination of emission sound pressure levels in situ using sound intensity". These standards must be used with suitable measuring instruments and corresponding evaluation software. Comparative measurements were conducted by a total of 17 European test houses. The investigations under real operating conditions included six differently sized machines. The comparison method according to EN ISO 3747 "Acoustics - Determination of sound power levels of noise sources using sound pressure - Comparison method for use in situ" was used to determine the sound power level; the results were compared to those of the proven sound intensity method according to EN ISO 9614- 2 "Acoustics - Determination of sound power levels of noise sources using sound intensity - Part 2: Measurement by scanning" and - as far as possible - to the reverberation room method in accordance with EN ISO 3741 "Acoustics - Determination of sound power levels of noise sources using sound pressure - Precision methods for reverberation rooms". The emission sound pressure level at the workplace was determined both in the framework of a sound pressure measurement according to EN ISO 11201 "Acoustics - Noise emitted by machinery and equipment - Measurement of emission sound pressure levels at a work station and at other specified positions - Engineering method in an essentially free field over a reflecting plane, EN ISO 11202 "Survey method in situ", EN ISO 11204 "Method requiring environmental corrections" and in the context of a sound intensity measurement as described in the draft paper ISO/CD 11205. These standards must be used with suitable measuring instruments and corresponding evaluation software.

Results:

It could be shown that the comparative method described in EN ISO 3747 is particularly suited for in situ use; it provides results attributable to precision class 2. The number of indicators could be reduced to only one, viz. the excess of sound pressure level under free field conditions. Among the standards relating to the determination of the emission sound pressure level at the workplace, EN ISO 1120 is only partly applicable, as the admissible environmental influence is low. Good reproducible results could be obtained using EN ISO 11202; these results, however, are slightly increased since the environmental correction is limited to 2.5 dB. It is recommended to increase the admissible environmental correction factor from 2.5 dB to 4 dB. In several cases EN 11204 could not be used at all or lead to larger deviations. The method should therefore be revised and further specified. The results obtained with the sound intensity method according to ISO 11205 are generally lower than those from the different sound pressure methods. As background noise may increase the deviation, this standard should be used under defined circumstances only. The project results were directly introduced into the standardisation discussion.

Publications:

Jonasson, H.G.: Determination of emission sound pressure level and sound power level in situ. Project SMT-CT 96- 2051, EC-DG XII; SP Report 1999: Acoustics, Boras 1999

Further informations:

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