Objective
In the first phase of the project, sound power levels of reference sound sources type B&K 4204 were measured by PTB and B&K using several different methods and acoustic environments. On the basis of the results, two methods were prescribed :
a) hemi-free field rooms, similar to the technique described in ISO 3745 : meridional scan using moving microphone and correction for air attenuation;
b) reverberation rooms, similar to the technique described in ISO 3741 : distribution of six discrete microphone and four source positions, and usage of reverberation time T15.
In the second phase of the project, sound power measurements on reference sound sources B&K 4204 were performed in an intercomparison among eight laboratories in seven hemi-free field rooms and in seven reverberation rooms. Personnel of the laboratories and of PTB calibrated the sources using the two prescribed methods.
The main results from the intercomparison are summarized as follows :
- Reproducibility of sound power measurements can be improved markedly by using the prescribed methods instead of the standardized methods used today.
- Measurements in hemi-free field rooms and in reverberation rooms give the same results, except in the frequency ranges below 100 Hz and above 10 kHz.
- Disturbing influences of the hemi-free field rooms are surprisingly small.
- Individual influences of reverberation rooms are important, but can be kept small with certain restrictions concerning volume and shape.
Several Community Directives require measurement of the sound power emitted by machines such as household appliances, those used in the work place and those used by the construction industry. Such measurement have to be made in accordance with many different national and international standards all of which basically reflect the requirements of the ISO 3740 series and ISO 9295. These latter standards are rated at different precision levels and the measurements made are not always in agreement with the required uncertainty limits for a particular class of machine.
The first phase of the project is for laboratories, PTB and Brüel and Kjaer, to investigate the different techniques available for the calibration of reference sound sources and agree calibrations for 4 selected sources. The second phase is an intercomparison of the calibration of sound power reference source involving the 6 - 8 different laboratories in Europe capable of such measurements. Finally, having agreed the calibration of the reference sources, they will be used in an intercomparison of sound power measurements by the substitution method in accordance with the draft revision of the ISO 3740 series.
STATUS
Phase 1 of the project has been completed. Calibrations of reference sound sources in reverberation rooms show systematic differences when different microphone arrangements are used, and it is concluded that more precise results are obtained with fixed microphone positions than with rotating microphone arrays. In the case of free-field measurements, it is concluded that a scanning microphone array (spiral path method) should be used instead of fixed microphone positions.
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Programme(s)
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Calls for proposals are divided into topics. A topic defines a specific subject or area for which applicants can submit proposals. The description of a topic comprises its specific scope and the expected impact of the funded project.
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Funding Scheme
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Funding scheme (or “Type of Action”) inside a programme with common features. It specifies: the scope of what is funded; the reimbursement rate; specific evaluation criteria to qualify for funding; and the use of simplified forms of costs like lump sums.
Coordinator
BRAUNSCHWEIG
Germany
The total costs incurred by this organisation to participate in the project, including direct and indirect costs. This amount is a subset of the overall project budget.