Archives of Acoustics, 34, 4, pp. 547-557, 2009

Selected Factors Affecting Uncertainty of All-Weather Microphones Research

Grażyna WSZOŁEK
AGH University of Science and Technology, Department of Mechanics and Vibroacoustics

Testing of devices for acoustic measurements in a
free-field are being performed at the stage of designing and type certification.
Free-field tests are performed only in a few laboratories - mainly in National
Metrology Institutes. These are: Danish Primary Laboratory of Acoustics (DPLA,
Denmark), Physikalisch Technische Bundesanstalt in Braunschweig (PTB, Germany),
National Physical Laboratory (NPL, United Kingdom) National Institute of
Standards and Technology (NIST, United States of America). The Vibroacoustic
Laboratory of the Department of Mechanics and Vibroacoustics, AGH is the only
place in Poland where this type of tests is performed. This is calibration
laboratory, which has an accreditation of Polish Centre for Accreditation (AP
022). Certain factors related to the determination of frequency and directivity
responses of all-weather microphones, which have a significant influence on the
uncertainty of the obtained results - are presented in the paper. The response
values, given below, indicate the calibration accuracy. This accuracy is
necessary since the aim of the measurements is to determine corrections and
designing of the proper compensating filters, which will allow to eliminate any
influence of devices on the acoustic field, the parameters of which are actually
under testing. This is directly related to the uncertainty assessment of
environmental measurements (e.g. to the accuracy of acoustic maps). The
necessity of collaboration of laboratories performing such tests and the need of
inter-laboratory comparisons is pointed out in the present paper. The
unification of the method of testing and the assessment of the uncertainty of
results seems to be necessary.
Keywords: all-weather microphones; free-field investigation; frequency responses; directional responses; Inter-Laboratory Comparisons
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