Acoustic metrology – an overview of calibration methods and their uncertainties

The paper gives a brief description of the principles and the uncertainty of the acoustic calibration methods that today are applied by National Metrology Institutes and calibration service centers. Even if some of the calibration principles have been applied over more than half a century, the methods and the instrumentation are still being refined in order to minimize their uncertainty, to extend their frequency ranges, to include extra parameters and to speed up slow processes. In addition to the traditional methods for microphone sensitivity and frequency response calibration, new development areas, like for example wind power, has created needs for low-frequency and infra-sound calibration, down to 0.1 Hz. Other high-tech areas have lead to the development of methods for phase response comparison calibration of microphones for large arrays, for sound intensity measurement and for verification of dynamic linearity of microphones at very high sound pressure levels, up to about 174 dB that corresponds to 10 kPa