Index of content:
Volume 119, Issue 1, January 2006
- ACOUSTICAL MEASUREMENTS AND INSTRUMENTATION 
119(2006); http://dx.doi.org/10.1121/1.2141360View Description Hide Description
A free-field (FF) substitution method for calibrating the pressure sensitivity of microphones at frequencies up to is demonstrated with both grazing and normal-incidence geometries. The substitution-based method, as opposed to a simultaneous method, avoids problems associated with the nonuniformity of the sound field and, as applied here, uses a air-condenser pressure microphone as a known reference. Best results were obtained with a centrifugal fan, which is used as a random, broadband sound source. A broadband source minimizes reflection-related interferences that can plague FF measurements. Calibrations were performed on FF air-condenser, electret, and microelectromechanical systems (MEMS) microphones in an anechoic chamber. The uncertainty of this FF method is estimated by comparing the pressure sensitivity of an air-condenser FF microphone, as derived from the FF measurement, with that of an electrostatic actuator calibration. The root-mean-square difference is found to be over the range , and the combined standard uncertainty of the FF method, including other significant contributions, is .