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Recent developments in the primary free-field reciprocity calibration of laboratory standard microphones at NPL - A contribution to Euromet project A295.

Barham, R G; Jarvis, D (1997) Recent developments in the primary free-field reciprocity calibration of laboratory standard microphones at NPL - A contribution to Euromet project A295. NPL Report. CIRA(EXT)019

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Abstract

Following an EC/BCR (Community Bureau of Reference) intercomparison on the primary free-field reciprocity calibration of laboratory standard microphones in 1991, discrepancies remained that could not be attributed to the measurement uncertainty claimed by the laboratories involved. This report describes research undertaken at NPL as part of a Euromet project aimed at discovering the causes of the discrepancies. In the case of calibrations undertaken at NPL, it is concluded that a small error may be caused by a reflection from the floor of the free-field chamber used, and that the effect of this reflection is similar to the introduction of an additional air attenuation factor. When the measured data is processed according to a theoretical model which accounts for this reflection, the frequency response for a given microphone becomes smoother and the repeatability of the measurements improves.

Item Type: Report/Guide (NPL Report)
NPL Report No.: CIRA(EXT)019
Subjects: Acoustics
Acoustics > Sound in Air
Last Modified: 02 Feb 2018 13:18
URI: http://eprintspublications.npl.co.uk/id/eprint/582

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