This part of IEC 1094 is applicable to laboratory standard microphones meeting the requirements of IEC 1094-1. The principles of the method are applicable to other types of microphones. In pa rticular, microphones which fulfil the requirements of IEC 1094-1, when fitted with a special adaptor, may also be calibrated according to this standard when the adaptor is removed. This part of IEC 1094 specifies a primary method of determining the free-field sensitivity so as to establish a reproducible and accurate basis for the measurement of sound pressure under free-field conditions. This part of IEC 1094 is intended for use by laboratories with highly experienced staff and specialized equipment.