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Training in Wideband Tympanometry
The development of absorbance measurements
Description
Summary of: Stinson, M. R., Shaw, E. A., & Lawton, B. W. (1982). Estimation of acoustical energy reflectance at the eardrum from measurements of pressure distribution in the human ear canal. The Journal of the Acoustical Society of America, 72(3), 766–773. https://doi.org/10.1121/1.388257
Tympanic membrane motion and impedance measurements become more complex as the stimulating acoustic energy increases above 2 kHz, which complicates evaluation of the underlying middle ear structures relative to lower frequencies. Energy reflectance via the standing wave ratio is relatively less sensitive to such complications. As such, this paper discusses the fraction of incident energy reflected from the eardrum and ear canal via the standing wave ratio (SWR) for comparison against alternative models of the middle ear of the time. This study analyzes 13 normal ears and reports values of SWR between the frequencies of 5 and 10 kHz. In general, the SWR (and associated energy reflection coefficient) is higher in the present study relative to other studies at the time for frequencies in the region of 7 to 8 kHz, corresponding to an energy reflectance of 60-78% as opposed to previously reported values approximating 40%. Importantly, this paper shows the general insensitivity of energy reflectance to probe position in the ear canal, which is one of the limitations of admittance tympanograms. This paper provides a historical glimpse of the early work involving energy reflectance, which eventually helped pave a path for future commercial development of wideband tympanometry as a metric of middle ear assessment.
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