ASA 130th Meeting - St. Louis, MO - 1995 Nov 27 .. Dec 01

5aPAb9. Measurement microphone calibrations and their uncertainty.

Erling Frederiksen

Danish Primary Lab. of Acoust. and Bruel & Kj(ae ligature)r, Transducer Products Div., 2850 N(ae ligature)rum, Denmark

Today, there is an increasing need for obtaining legal acceptance of and confidence in calibrations performed by laboratories in other countries. This is especially true and clearly observable in Europe where the number of accredited laboratories and calibrations per year are rapidly increasing. To obtain accreditation the laboratories must analyze and state their calibration uncertainty. This leads to focus on uncertainty of microphone sensitivity and sound level calibrations. The overall calibration uncertainty valid for ordinary measurement microphones and pistonphones have been determined by studying error sources and their influence on the calibration results. The uncertainties of the methods, which directly and indirectly influence the uncertainty valid for the user of a Bruel & Kj(ae ligature)r transducer calibration, are discussed. The methods include free-field and pressure reciprocity calibration of refrence standard microphones performed by the Danish Primary Laboratory of Acoustics (operated by Bruel & Kj(ae ligature)r in cooperation with the Danish Technical University, Lyngby) and the electrostatic actuator method which is widely applied by the Bruel & Kj(ae ligature)r Production Department and Calibration Service Centers. Contributions to the uncertainty which are due to the free-field and diffuse-field corrections and to the influence of microphone protection grids will be presented.