IMPEDANCE AUDIOMETRY

Impedance in audiometry is the opposition the middle ear presents to the flow of sound energy. It combines resistance (friction) and reactance (mass and stiffness) and affects sound transmission to the inner ear. Measured indirectly by tympanometry or acoustic reflex testing, abnormal impedance patterns indicate middle‑ear conditions (e.g., fluid, eardrum perforation, ossicular fixation) that alter hearing.

The impedance test (tympanometry) assesses middle-ear function by measuring eardrum movement and middle-ear pressure. It helps detect fluid behind the eardrum, eustachian tube dysfunction, perforation, and ossicular chain problems, and aids in distinguishing conductive from sensorineural hearing loss. It’s used in routine hearing evaluations, newborn screening, and monitoring ear infections or middle-ear status during treatment.

PTA (pure tone audiometry) measures hearing sensitivity by determining the softest tones a person can hear across frequencies, reported in decibels. Impedance (tympanometry/immittance) evaluates middle‑ear mechanics—eardrum mobility, middle‑ear pressure and ear‑canal volume—to detect fluid, perforation or Eustachian tube dysfunction. They are complementary in ear assessment.

Impedance is the physical resistance and reactance of the middle‑ear system to sound (including stiffness, mass, and friction). Tympanometry is a diagnostic test that varies ear‑canal pressure while delivering a tone to measure tympanic membrane and middle‑ear mobility (admittance/compliance), producing a tympanogram. In short, impedance is what’s measured; tympanometry is the method used to measure it.

There isn’t a single “normal” impedance number; audiology uses admittance (compliance) instead. Normal tympanometry shows peak compliance about 0.3–1.6 mL (or mmho) with peak middle-ear pressure roughly −100 to +50 daPa. Impedance is the inverse of admittance: higher impedance suggests stiffness or fluid, lower impedance suggests overly mobile system. Values must be interpreted with clinical findings.

Impedance in hearing is the ear’s opposition to sound energy transfer through the middle ear. It depends on stiffness, mass and damping of the eardrum and ossicles and varies with frequency. Clinically it’s measured by tympanometry. Increased impedance (e.g., fluid or stiff middle ear) reduces sound transmission and causes conductive hearing loss; proper impedance matching aids efficient hearing.