Static acoustic-immittance measurements.

The basic principles of deriving static acoustic-immittance measurements in human ears are presented. Problems caused by differences in instrumentation, computations, and measurement technique are discussed in terms of the utility and comparisons of static acoustic-immittance measurements. Data are provided regarding the short- and long-term variabilities inherent to static measurements. Although our subject pool was relatively small, certain patterns were apparent in the short- and long-term variability inherent to static acoustic-impedance measurements. The intra-event variability about the mean static acoustic impedance was small and varied inversely with probe-tone frequency. Standard deviations were less than 50 acoustic ohms for a 220-Hz probe tone and less than 25 acoustic ohms for a 660-Hz probe tone. Session-to-session variability in static measurements varied little within subjects but varied greatly across subjects. There was little correlation between the mean and standard deviation for within-subject measurements. Standard deviations across subjects approximate a relatively constant proportion (30-40%) of the mean static value. The need for large population studies of static acoustic-immittance measurements is noted.