This part of IEC61094 specifies a primary method of determining the complex free-field sensitivity of laboratory standard microphones so as to establish a reproducible and accurate basis for the measurement of sound pressure under free-field conditions, is applicable to laboratory standard microphones meeting the requirements of IEC61094‑1 , is intended for use by laboratories with highly experienced staff and specialized equipment. NOTE The calibration principle described in this part of IEC61094 is also applicable to working standard microphones, preferably used without their protection grid.