Impedance Audiometry (Tympanometry): Middle Ear Resistance, Test Results & ENT Guide

Impedance audiometry might be the most underrated test in all of ear medicine. Think about that for a second. You can hear perfectly well on a standard hearing test – pass it with flying colours – and still have a very real, very fixable problem sitting right behind your eardrum. Fluid quietly pooling in the middle ear. A Eustachian tube that stopped doing its job months ago. A tiny bone that’s gotten stiff without anyone noticing. None of this shows up on a regular audiogram. But tympanometry – the core component of impedance audiometry – catches all of it.

I’ve seen parents bring in kids who’ve been struggling at school for a year, teachers thinking the child just “isn’t paying attention.” Turned out, both ears were full of fluid. One quick tympanogram told us more in 90 seconds than weeks of wondering. That, honestly, is what makes this test worth knowing about.

What Is Impedance Audiometry?

Here’s the simplest way to put it: impedance audiometry measures how easily sound energy moves through your middle ear. Not whether you hear the sound – that’s a different question entirely. This test is specifically about mechanics. About whether the moving parts of the middle ear – the eardrum, the three tiny bones, the air pressure balance – are actually working the way they should.

The word “impedance” sounds a bit forbidding, I know. But it just means resistance – how much the eardrum and its attached structures resist being pushed around by sound waves. Too much resistance? That usually means stiffness or fluid. Too little? Could be a broken ossicular chain. The test quantifies this resistance and plots it as a graph called a tympanogram. And from that curve, a trained ENT can read a surprising amount of information.

Impedance Audiometry vs. Standard Audiometry – What’s the Difference?

This difference matters enormously when you’re dealing with children, elderly patients, or anyone who finds it difficult to reliably respond to tones. Impedance audiometry requires nothing from the patient except a reasonably quiet ear canal and a few seconds of stillness.

Why the Middle Ear Deserves More Attention Than It Gets

Most people know about the eardrum and vaguely know there’s something “inner” about hearing. But the middle ear – that tiny air-filled space between the drum and the cochlea – is where a remarkable amount of trouble quietly starts. It houses three of the smallest bones in the human body (the ossicular chain), and it depends on the Eustachian tube to stay at the right pressure. When either of those systems fails, hearing suffers. And often, nothing hurts. That’s the tricky part.

How the Test Actually Works

Equipment and Procedure

The device used is called a tympanometer – a small handheld instrument with a soft probe tip that sits gently in the opening of your ear canal. It doesn’t go deep. It seals the canal just enough to control air pressure, then delivers a low-frequency tone (usually 226 Hz, though higher frequencies are used in infants) while varying the pressure from positive to negative.

As pressure changes, the device measures how much sound energy bounces back from the eardrum – this is the acoustic immittance. A healthy, mobile eardrum absorbs energy efficiently at normal (atmospheric) pressure. A stiff eardrum, or one weighed down by fluid, bounces energy back differently. The machine plots all this as a tympanogram in real time.

If the full test includes acoustic reflex testing, there’s an extra step: brief loud tones are used to trigger the stapedius muscle reflex (a tiny protective muscle in the middle ear). The presence, absence, or latency of this reflex adds yet another layer of diagnostic information – particularly useful when evaluating for facial nerve problems or auditory processing issues.

What You Actually Feel During the Test

Honestly? Not much. There’s a soft tip placed at the entrance of your ear, a brief sensation of pressure – similar to what happens when a lift descends or a plane starts landing – and that’s mostly it. Some people find the sensation mildly strange. Children occasionally flinch. But pain? No. The whole process takes about a minute per ear. Immediately after, results are visible on screen. There’s no recovery time, no side effects, and no prep needed on your end.

Understanding What the Results Show

Tympanogram Types: What Each Curve Means

The tympanogram is a curve on a graph – the Y-axis shows compliance (how easily the eardrum moves), and the X-axis shows air pressure (measured in daPa). The shape of this curve is everything. Audiologists and ENT specialists use a classification system – originally described by Jerger in 1970 and still widely used today – that categorises results into five main types.

Common Conditions Identified by Tympanometry

Fluid in the Middle Ear (Otitis Media with Effusion)

This is genuinely the single most common finding in paediatric ENT, and tympanometry is the most reliable non-invasive way to detect it. When the middle ear fills with thick, glue-like fluid – often following a cold, an ear infection, or simply poor Eustachian tube function – the eardrum can no longer vibrate freely. The result is a Type B tympanogram, and often a mild to moderate conductive hearing loss on the audiogram. Children with this condition are sometimes misidentified as inattentive or developmentally delayed. Getting the diagnosis right changes everything for them and their families.

Eustachian Tube Dysfunction

The Eustachian tube runs from the middle ear to the back of the throat and is supposed to equalise pressure every time you swallow or yawn. When it stops doing that – whether from congestion, inflammation, or anatomical quirks – negative pressure builds up in the middle ear. This causes that characteristic feeling of a “blocked” ear, muffled hearing, and sometimes mild pain. The tympanogram will typically show a Type C result: a peak that’s shifted well into negative pressure territory. Often this resolves on its own, but persistent Type C patterns are worth following up.

Eardrum Abnormalities

Perforations – holes in the eardrum from infections, trauma, or previous grommets – produce a distinctive flat tympanogram with a high ear canal volume. Tympanosclerosis (calcification of the drum or middle ear structures) tends to show a Type As pattern. Interestingly, a healed perforation site can sometimes create a “flap” that’s more mobile than normal, causing an Ad pattern even when there’s no active disease. These nuances are exactly why tympanometry results are always read in clinical context – numbers alone don’t tell the whole story.

Interpreting Results: Patterns, Cases & When to Worry

Real-World Clinical Scenarios

Scenario 1 – The child who keeps missing things: A 6-year-old whose teacher says he’s “not listening.” His parents notice he turns the TV up louder than his siblings. Pure-tone audiogram shows mild bilateral conductive hearing loss. Tympanometry: flat Type B, both ears. Canal volumes normal. Diagnosis: bilateral otitis media with effusion (glue ear). After treatment, his classroom performance improved markedly. The tympanogram was the piece that made everything click.

Scenario 2 – The adult with blocked ears after a cold: A 34-year-old woman presents two weeks after a viral upper respiratory infection, complaining her left ear still feels “like it’s underwater.” Otoscopy looks near-normal – just slightly retracted eardrum. Tympanogram: Type C at -180 daPa. No fluid yet, but Eustachian tube is clearly struggling. Managed conservatively with nasal decongestants and followed up. Resolved within three weeks.

Scenario 3 – The older adult with gradually worsening hearing: A 62-year-old man whose audiogram shows moderate conductive hearing loss. Tympanometry: Type As – shallow peak suggesting stiffness. CT temporal bones confirms otosclerosis. This man had been told for years he was “just getting old.” Impedance audiometry was the first objective clue that something structural was going on.

When Should You Actually See an ENT?

A single mildly abnormal result after a cold is often not cause for immediate concern. Patterns matter more than isolated findings. Your GP or audiologist can guide you, and a good ENT service will tell you honestly when watchful waiting is the right call.