Primary calibration of measurement microphones in the world: state of art

T A B Milhomem,Z M D Soares

doi:10.1088/1742-6596/733/1/012054

Abstract

This paper presents an overview of state of art of measurement microphones primary calibration in the world with emphasis on Brazil practices. Initially, pressure field calibration is summarized being discussed mainly the couplers used to create pressure field conditions. After that, free-field calibration is presented being commented especially the anechoic chambers used to create free-field conditions. Concluding, it is showed diffuse-field calibration that is being investigated. It is presented, in particular, the reverberant chambers used to create diffuse-field conditions.

Highlights

Calibration of a measurement microphone commonly consists in determining its sensitivity as a function of frequency, i.e., determining the ratio between the incident sound pressure and the emerging voltage as a function of frequency
Primary calibration of measurement microphones usually is performed by the reciprocity method using three microphones
From the determined impedances for each pair of microphones, the sensitivity of each microphone is calculated [1,2,3]. Such as sensitivity changes according to the sound field, three theoretical sound fields were established for calibration purposes: pressure field, free-field and diffuse-field [1]

Summary

INTRODUCTION

Calibration of a measurement microphone commonly consists in determining its sensitivity (modulus and phase) as a function of frequency, i.e., determining the ratio between the incident sound pressure and the emerging voltage as a function of frequency. Primary calibration of measurement microphones usually is performed by the reciprocity method using three microphones. Following this method, the microphones are acoustically coupled in pairs and using one of them as sound source (transmitter microphone) and other as sound receiver (receiver microphone), the electrical and acoustic transfer impedances are determined (figure 1). From the determined impedances for each pair of microphones, the sensitivity of each microphone is calculated [1,2,3] Such as sensitivity changes according to the sound field, three theoretical sound fields were established for calibration purposes: pressure field, free-field and diffuse-field [1]. 8th Brazilian Congress on Metrology, Bento Gonçalves/RS, 2015 1 microphones primary calibrations in the world with emphasis on Brazil practices

PRESSURE FIELD PRIMARY CALIBRATION

DIFFUSE-FIELD PRIMARY CALIBRATION

REFERENCE