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Acoustic impedances of audiometric earphones coupled to different loads

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Disciplines
  • Musicology
  • Physics

Abstract

The acoustic impedance of an audiometric earphone is one of the factors that can affect sound transmission through the ear during tests of hearing sensitivity. Similar situation exists during calibration of the earphone where its impedance can affect sound transmission through a coupler. The importance of this impedance is related to the contribution of other elements involved in transmission such as ear canal impedance or impedance of the coupler seen from outside. In order to determine the acoustic impedances of five audiometric earphones, the standardized method for measurement of complex impedances is applied, which is based on the transfer function between two microphone locations in an impedance tube. For that purpose, the special measuring tube containing four microphones is developed, where different pairs of microphones are used for different frequency ranges. During the measurements, audiometric earphones are coupled to different loads. Thus, they are placed on different terminations of the tube including metal plate, artificial rubber pinna and upper part of the standardized coupler. The results show that the impedances of earphones are different, but they also differ from radiation impedances of used terminations (seen from inside the tube without earphone). In addition, there is an indication of differences among the earphones regarding the influence of the load on their impedances. These results are going to be further analysed together with the corresponding ones obtained in investigations of coupling of audiometric earphones to human ears and to the same coupler.

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