Summary of: Voss, S. E., Stenfelt, S., Neely, S. T., & Rosowski, J. J. (2013). Factors that introduce intrasubject variability into ear-canal absorbance measurements. Ear and hearing, 34 Suppl 1(7 0 1), 60S–64S. https://doi.org/10.1097/AUD.0b013e31829cfd64
Wideband tympanometry is useful for investigating how acoustic energy flows through the ear as well as diagnosing conductive hearing loss. And, understanding the individual variability is essential for the interpretation of individual measurements. This article discusses the contributions to of variability to intrasubject variability in ear-canal-absorbance-based measurements. Such contributors to intrasubject variability include ear-canal static pressure or middle-ear fluid, probe orientation. Other factors, albeit small, may include additional loss along the ear-canal wall based on probe placement, e.g., more losses may coincide with more lateral probe placement, or non-uniformity of the cross sectional area of the ear canal. However, the one of the larger sources of variability relate to the acoustic seal between the surface of the earphone tip and the walls of the ear canal. If small leaks occur that allow acoustic energy to escape the ear canal, large errors in absorbance and subsequent large intra-subject variability may occur. High absorbance below 500 Hz is a strong indicator of such a leak. Test-retest variability in adults in lower than in infants but can also add to intra-subject variability. This suggests that the wideband absorbance measures in the Titan probe are stable so long as the user controls for acoustic leaks.