Winfried Krebber Stefan Bohme
[Inst. for Commun. Eng., Aachen Univ. of Technol. RWTH), Melatener Str. 23, D-52056 Aachen, Germany], and
Hans W. Gierlich
HEAD Acoustics GmbH, Herzogenrath, Germany
Opinion tests show the importance of the acoustical leakage between the handset and the human ear for the subjective speech transmission quality of telephone sets. Artificial ears, which are now used for telephone measurements, do not allow measurements with variable leakage. Using an artificial ear formed as an individual human ear does not lead to reproducible results. Both problems are avoided by this new ear. It has a simplified shape, which is determined by only a few geometrical parameters. Thus the transmission characteristics can be described by a mathematical model. Nevertheless it approximates a human ear, referring to the dependence of the leakage and the transmission characteristics on the force applied to the handset. Measurements using the artificial ear are reproducible and show high conformity with measurements of handsets at human ears. Implemented in an artificial head, the ear can also be used to measure hands-free telephones. The directional characteristics of the artificial ear in a free sound field show all main structures of monaural outer ear transfer functions.