[Mechanical impedance of the human mastoid and forehead--a critique of the mechanical coupler of the IEC373].
Mechanical impedances of human mastoids and foreheads were measured on frequencies from 250 to 6300 Hz for 80 young adults by means of B&K impedance head (#8000) and shaker (#4810) as main parts of the measuring setup. The measurements revealed the following problems in the IEC373 (1971/1981) which had defined the mechanical impedance characteristics of the mechanical coupler for calibration of bone vibrators in audiometric use. The average impedance levels of the mastoids differ significantly from those of the foreheads in middle and high frequencies. The impedance levels of the IEC373 mechanical coupler are higher than those of the present measurements of the mastoids and the foreheads. The differences exceeded the tolerance limits of IEC373 (1981) in every frequency. These findings strongly suggest that the coupler is neither the artificial mastoid nor the artificial forehead but a coupler having a specified impedance, therefore, disregard for effect of the type of bone vibrator on the Reference Equivalent Threshold Force Level, as seen in ISO7566, should be revised and that the RETFL should be determined for an each type of bone vibrator.
Takeuchi
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Y
Department of Otolaryngology, Kitasato University, Medical School, Kanagawa.
D000328:Adult; D001696:Biomechanical Phenomena; D001844:Bone Conduction; D004582:Electronics, Medical; D005260:Female; D005546:Forehead; D005624:Frontal Bone / Q000502:physiology*; D006801:Humans; D008297:Male; D008416:Mastoid / Q000502:physiology*; D012015:Reference Standards; D012952:Societies; D014732:Vibration