Measurement of the local power reflection coefficient in the ear canal using the two-microphone method
William J. Murphy, Arnold Tubis, Glenis R. Long · The Journal of the Acoustical Society of America · 1989
The local power reflection coefficient in the ear canals of humans has been measured using the two-microphone technique [W. J. Murphy, A. Tubis, and G. R. Long, J. Acoust. Soc. Am. Suppl. 1 82, S70 (1987)]. The accuracy of the calibration technique and the assessment of the random and bias errors associated with the reflectance have been investigated. The use of bandlimited noise as a stimulus results in decreased coherence between the two microphone signals relative to the coherence obtained with sinusoidal or other deterministic signals (e.g., a chirp signal) at high frequencies. The effects on the coherence and the reflectance due to sinusoidal chirp and bandlimited stimuli are presented. The measurements were performed in an acrylic hard-terminated tube. As a test of the assumption of local one dimensionality of the ear canal, the reflectance was measured as a function of the insertion depth of the two-microphone probe in several subjects. At high frequencies, the measured reflectance was found to vary significantly in ear canals with contorted geometries. In relatively straight ear canals, the measured reflectance was found to vary by less than 10% for changes of 5 mm in the insertion depth. [Work supported by a grant from the Deafness Research Foundation.]