3aSP7. Comparison of acoustic reflectance measurement techniques.

Session: Wednesday Morning, June 18

Author: Douglas H. Keefe
Location: Boys Town Natl. Res. Hospital, 555 N. 30th St., Omaha, NE 68124, keefe@boystown.org


Acoustic reflectance measurement techniques have been investigated that are calibrated using pressure responses measured in one or more cylindrical tubes and viscothermal models of wall loss. Of clinical interest as a test of hearing is a single-microphone technique to measure the inherently nonlinear ear-canal reflectance at various stimulus levels. Calibration of the probe containing the sound source/receiver consists of measuring the source reflectance of the probe and the incident pressure response at each stimulus level. A single-tube technique relies on separability of the tube response into incident and reflected signals, while multi-tube techniques rely on solving an overdetermined matrix equation of responses. The matrix includes weighting factors that differ across tubes by reflectance or SPL to control for inadequate signal-to-noise ratios at isolated frequencies, and a regularized matrix inverse solution is compared to the pseudoinverse solution. The single-tube technique functions as well as the best performing multi-tube technique, and requires fewer calibration steps. However, there is an ambiguity between the tube length chosen in the tube response model and the measured phase of the source reflectance. This ambiguity is addressed by a priori knowledge of the phase response of the probe averaged across frequency.

ASA 133rd meeting - Penn State, June 1997