Nearly all audiometric tests are carried out with headphones or insert earphones, and it is characteristic that the driving voltage of the transducer is controlled very precisely, whereas no measurement takes place of the actual eardrum exposure of the person being tested. Instead, a calibration procedure is regularly carried out, in which the connection between voltage at the transducer terminals and the resulting sound pressure is registered by the equipment. During this calibration the transducer is loaded with a coupler that simulates acoustically an average human ear, and it is the idea that the transducer will supply the same sound to a person under test. Unfortunately, this only holds to a limited extent, and in general the precise sound exposure of the eardrum of an individual is more or less unknown and insufficiently controlled. In the initial phase, this project has focused on an assessment of the loading of the headphone, when placed on humans versus the coupler used for calibration. Currently, the acoustic impedances of audiometric earphones coupled to different loads are determined using a measuring tube. Supported by STVF/FTP.