Tympanometry explained: what the pressure test measures and why

What tympanometry is

Tympanometry is a quick, objective measurement of how well the eardrum (tympanic membrane) and the middle-ear system move in response to controlled changes in air pressure. It does not measure whether you can hear sounds; it measures the mechanical function of the structures that transmit sound from the ear canal to the inner ear.

The test takes roughly 10 to 20 seconds per ear and requires no active response from the patient, making it useful across all age groups including infants.

How the test works

An audiologist or hearing health professional places a small, soft probe tip in the entrance of the ear canal to create a seal. The probe contains three tiny components: a speaker, a microphone, and a pressure pump.

The pump slowly sweeps air pressure from positive (above atmospheric) to negative (below atmospheric) while the speaker emits a low-frequency tone, typically 226 Hz for adults and 1000 Hz for infants. The microphone measures how much of that tone is absorbed by the eardrum versus reflected back.

When the eardrum is at its most mobile, it absorbs sound most efficiently. The point at which absorption peaks corresponds to the air pressure at which the middle-ear system is in equilibrium. That peak is plotted on a graph called a tympanogram.

Reading the tympanogram

The x-axis of a tympanogram shows air pressure in decapascals (daPa). The y-axis shows acoustic admittance, a measure of how easily energy flows through the system. Higher admittance means the eardrum is moving more freely.

Type A

A Type A tympanogram has a single, symmetric peak near 0 daPa with admittance in the normal range (roughly 0.3 to 1.7 millimhos for adults, though laboratories vary slightly). This pattern indicates normal middle-ear pressure and normal eardrum compliance. The American Academy of Audiology and the NHS UK both list Type A as the expected result in a healthy ear.

Type As

Type As (shallow) has the peak in the right location but the admittance value is lower than normal. It suggests reduced eardrum compliance, often associated with otosclerosis, a condition in which abnormal bone growth stiffens the ossicular chain.

Type Ad

Type Ad (deep or discontinuous) has an abnormally high or broad peak. This pattern can indicate a flaccid or perforated eardrum, or a disrupted ossicular chain where one of the three tiny middle-ear bones has separated.

Type B

A Type B tympanogram is flat. No peak appears. This is the most clinically significant pattern and indicates that the eardrum is not moving. Common causes include fluid in the middle-ear space (otitis media with effusion, sometimes called “glue ear”), a tympanic membrane perforation, or the probe being blocked by earwax. AAO-HNS guidelines for otitis media with effusion rely heavily on Type B findings as part of the diagnostic criteria.

Type C

Type C shows a peak that has shifted to the negative pressure side (generally below -150 daPa). This indicates negative middle-ear pressure, often reflecting eustachian tube dysfunction, the tube that normally equilibrates pressure between the middle ear and the back of the throat. Many people develop transient Type C patterns during or after upper respiratory infections.

What tympanometry finds and what it misses

Tympanometry is particularly valuable for detecting middle-ear effusion in children, assessing eustachian tube function, identifying ossicular discontinuity, and flagging eardrum perforations before other procedures. It is a standard part of any pediatric hearing evaluation and is also used before and after middle-ear surgeries to track outcomes.

However, tympanometry does not assess the inner ear or auditory nerve. A person with profound sensorineural hearing loss, meaning damage to the cochlear hair cells or auditory nerve, can have a perfectly normal tympanogram. Similarly, tympanometry does not directly test how well speech is understood.

The test is sensitive to probe fit. If the probe tip does not seal the ear canal properly, the result will be unreliable. Earwax buildup can also block the probe and produce a flat-looking trace that does not reflect actual middle-ear function.

Tympanometry in infants

Infants under six months are typically tested with a 1000 Hz probe tone rather than the standard 226 Hz used in adults. The infant ear canal is more compliant and cartilaginous, meaning lower-frequency tones can produce misleading results. The NIDCD notes that universal newborn hearing screening programs often combine otoacoustic emission testing with tympanometry or auditory brainstem response measures to build a fuller picture.

Tympanometry and eustachian tube function

The eustachian tube connects the middle-ear space to the nasopharynx and normally opens briefly during swallowing or yawning to equalize pressure. When it fails to open adequately, negative pressure builds in the middle ear, pulling the eardrum inward and reducing its mobility.

A related and opposite condition, patulous eustachian tube, occurs when the tube fails to close properly. In that case, patients often report hearing their own breathing and voice abnormally loudly (autophony). Tympanometry findings in patulous eustachian tube can fluctuate with respiration, sometimes showing pressure excursions synchronized with breathing.

What happens after the test

Tympanometry results are interpreted alongside pure-tone audiometry, otoscopy, and the patient’s history. A single test type rarely tells the whole story. If the result is abnormal, the next steps depend on the pattern and clinical picture, and may include referral to an ear, nose, and throat physician, imaging, or monitoring over time.

If symptoms persist or change, see an audiologist or physician.