This part of IEC 61094 " is applicable to laboratory standard microphones meeting the requirements of IEC 61094-1, " specifies a primary method of determining the complex free-field sensitivity so as to establish a reproducible and accurate basis for the measurement of sound pressure under free-field conditions, " is intended for use by laboratories with highly experienced staff and specialized equipment. NOTE The calibration principle described in this part of IEC 61094 is also applicable to working standard microphones, preferably used without their protection grid.