| 1. |
- Brezas, Spyros, et al.
(författare)
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Dissemination of the unit watt in airborne sound : Aerodynamic reference sound sources as transfer standards
- 2016
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Ingår i: Proceedings of the INTER-NOISE 2016 - 45th International Congress and Exposition on Noise Control Engineering. - 9783939296119 ; , s. 6762-6770
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Konferensbidrag (refereegranskat)abstract
- In the process aiming at the establishment of both traceability and transparent uncertainty budgets for airborne sound power, the dissemination of the unit watt ensures the correct relation between the sound power of a stationary primary standard and the sound power of transportable transfer standards. The paper reports on a detailed study to qualify aerodynamic reference sound sources (RSSs) as transfer standards. The temporal stability of RSSs has been determined for both narrow and broad frequency bands. Specially designed scanning apparatuses have provided directivity results. Remaining room reflections and near field effects have also been studied. The dissemination also requires the prediction of sound power under meteorological (static pressure, ambient temperature) and operating (rotational speed) conditions different from calibration conditions. These influences have been investigated and a correction is proposed. Finally, interlaboratory measurement results of the sound power of an aerodynamic reference sound source are reported.
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| 2. |
- Cellard, Patrick, et al.
(författare)
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Automatic sound field sampling mechanisms to disseminate the unit watt in airborne sound
- 2016
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Ingår i: Proceedings of the INTER-NOISE 2016 - 45th International Congress and Exposition on Noise Control Engineering. - 9781510829886 ; , s. 6757-6761
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Konferensbidrag (refereegranskat)abstract
- For the dissemination of the unit watt, the sound pressures emitted by primary and secondary sound power standards are to be measured. Disseminating the unit in reverberant fields requires the measurement of a volume average whereas in hemi-anechoic fields, measurements on an enveloping surface are appropriate. For the latter situation, automatic sound field scanning mechanisms were developed by LNE, SP and PTB. At PTP, an arc with 24 microphones is used which can be tilted to cover a hemispherical measurement surface. Different radii can be realised by manual adjustment of the microphones. At SP, a single microphone is moved on a semi-circular arc. Different latitudes can be realised by manual arrangements. LNE developed a scanning mechanism consisting of a hemi-circular arc. A microphone can be positioned on arbitrary altitude positions on the arc and the arc can move on a circular path. This way, arbitrary positions on a hemispherical measurement surface can be realised. The contribution introduces the different mechanisms and lists advantages and disadvantages of the different technical solutions.
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