Free-field reciprocity calibration of laboratory standard (LS) microphones using a time selective technique

Knud Rasmussen, Salvador Barrera Figueroa

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Abstract

Although the basic principle of reciprocity calibration of microphones in a free field is simple, the practical problems are complicated due to the low signal-to-noise ratio and the influence of cross talk and reflections from the surroundings. The influence of uncorrelated noise can be reduced by conventional narrow-band filtering and time averaging, while correlated signals like cross talk and reflections can be eliminated by using time-selective postprocessing techniques. The technique used at DPLA overcomes both these problems using a B&K Pulse analyzer in the SSR mode (steady state response) and an FFT-based time-selective technique. The complex electrical transfer impedance is measured in linear frequency steps from a few kHz to about three times the resonance frequency of the microphones. The missing values at low frequencies are estimated from a detailed knowledge of the pressure sensitivities. Next an inverse FFT is applied and a time window around the main signal is used to eliminate cross talk and reflections. Finally, the signal is transformed back to the frequency domain and the free field sensitivities calculated. The standard procedure at DPLA involves measurements at four distances and the repeatability of the calibrations over time is within ±0.03 dB up to about 1.5 times the resonance frequency of the microphones.
Original languageEnglish
Title of host publicationJournal of the Acoustical Society of America
Number of pages3232
Volume120
Publication date2006
Publication statusPublished - 2006
EventJournal of the Acoustical Society of America -
Duration: 1 Jan 2005 → …

Conference

ConferenceJournal of the Acoustical Society of America
Period01/01/2005 → …

Bibliographical note

Copyright (2006) Acoustical Society of America. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the Acoustical Society of America.

Cite this

Rasmussen, K., & Barrera Figueroa, S. (2006). Free-field reciprocity calibration of laboratory standard (LS) microphones using a time selective technique. In Journal of the Acoustical Society of America (Vol. 120)