Evaluation of a New Artificial Mastoid as an Instrument for the Calibration of Audiometer Bone-Conduction Systems

Abstract

A basic problem in obtaining dependable bone-conduction thresholds in pure-tone audiometry has been the attainment of an objective measure of the vibrational output of the system. In the past, several different artificial-mastoid designs have been reported, but none has proved entirely satisfactory as a standard calibration instrument, largely because of the problems involved in devising a stable and reproducible method of terminating the bone vibrator with a mechanical impedance that simulates that of the average human mastoid. In the present study, a new artificial mastoid, Beltone model 4, was analyzed for stability of response and for its potential use as a calibration instrument. Two bone vibrators were used for repeated measurements over a period of time to establish the reliability and linearity of the measuring instrument. Normative data were then derived from a suitable sample of normal-hearing subjects for one of the vibrators. These data were then transferred to other vibrators of the same type via the artificial mastoid, and bone-conduction thresholds were measured for the criterion sample of normal-hearing subjects and for subjects with sensorineural hearing impairments. Results suggest that the new artificial mastoid has good stability and that it shows excellent promise as an instrument for the calibration of bone-conduction audiometers.