Relationship Between 226-Hz Single Frequency Static Admittance and Wideband Absorbance in Adults with Normal Hearing

Single-frequency tympanometry using a 226-Hz probe tone is routinely employed to evaluate middle-ear function. However, individuals with normal hearing may exhibit different tympanometric subtypes (types A, As, and Ad), reflecting variations in middle-ear mechanics. Whether these differences correspond to systematic changes in wideband absorbance (WBA) remains unclear.

Sixty ears from adults aged 18-35 years with normal hearing sensitivity were included. Based on conventional tympanometry, ears were categorized into types A, As, and Ad groups (20 ears each). Wideband absorbance was measured from 250 to 8000 Hz under ambient and peak pressure conditions. Mixed repeated-measures analysis of variance assessed the effects of pressure, frequency, and tympanometric subtype on absorbance. Post-hoc comparisons identified intergroup differences, and correlation analysis examined the relationship between 226-Hz static admittance and WBA.

Absorbance was higher at peak than ambient pressure across groups, with the greatest differences at lower frequencies. Distinct absorbance patterns emerged among tympanometric subtypes, particularly in the low- to mid-frequency range. Under peak pressure, significant differences extended to 1250 Hz between types A and As ears and to 3000 Hz in comparisons involving type Ad. Static admittance showed a strong positive correlation with WBA up to approximately 3 kHz, weakening at higher frequencies.

Tympanometric subtypes in normal-hearing adults are associated with measurable differences in wideband energy transmission. Integrating WBA with conventional tympanometry may enhance clinical interpretation by providing a more comprehensive view of middle-ear function.