How to Read a Tympanogram and Interpret the Results

A tympanogram is a graph that shows how well your eardrum moves in response to changes in air pressure, and reading one comes down to three things: where the peak sits along the pressure axis, how tall the peak is, and whether there is a peak at all. These features are classified into a handful of patterns, most commonly labeled Type A, B, and C, each pointing toward a different condition in the middle ear. The system is intuitive once you know what each axis represents, but the details matter because small shifts in the curve can change the clinical picture considerably.

What the Graph Actually Shows

The horizontal axis of a tympanogram represents air pressure in the ear canal, measured in decapascals (daPa). Zero sits in the middle, meaning atmospheric pressure. Negative values stretch to the left, positive to the right. The vertical axis represents compliance (sometimes called admittance), which is essentially how easily sound energy passes through the eardrum and into the middle ear. The unit is usually milliliters (mL) or cubic centimeters (cc), which are interchangeable for practical purposes.

During the test, a small probe sealed in the ear canal sweeps the pressure from positive to negative while playing a low tone, typically at 226 Hz. As pressure changes, the eardrum stiffens or loosens. The point where it moves most freely produces the peak of the tympanogram. That peak tells you two things at once: its height reveals how compliant the eardrum system is, and its position along the pressure axis reveals the pressure inside the middle ear space behind the drum.

Type A: The Normal Pattern

A Type A tympanogram has a well-defined peak near 0 daPa, meaning the pressure on both sides of the eardrum is roughly equal. The peak height in adults usually falls somewhere between about 0.3 and 1.5 mL, though normal ranges vary somewhat by age and sex. This pattern tells you the middle ear system is working the way it should: the eardrum is intact, the ossicles (the tiny bones behind it) are mobile, and there is no significant fluid buildup.

Two important subtypes live under the Type A umbrella. A Type As tympanogram (“s” for shallow or stiff) has a peak that is unusually low, meaning the system is stiffer than normal. This pattern shows up in conditions where something restricts the movement of the eardrum or ossicular chain, with otosclerosis being the classic example. In otosclerosis, abnormal bone growth around the stapes footplate limits how much the chain can vibrate. Testing for this condition often pairs the tympanogram with acoustic reflex testing, since absent reflexes alongside a shallow peak strengthens the suspicion. One study found that ears with diagnosed otosclerosis more frequently showed absent acoustic reflex thresholds and distinct absorbance patterns compared to normal ears.¹

A Type Ad tympanogram (“d” for deep or disarticulated) is the opposite: the peak shoots unusually high, sometimes off the chart. This suggests the system is hypercompliant, moving too freely. The textbook explanation is ossicular chain discontinuity, where a break in the chain of tiny bones removes the normal resistance, or a very thin, scarred eardrum (a monomeric membrane) that flaps easily. However, research has shown that eustachian tube dysfunction and other non-structural factors can also produce this overly tall peak, so a Type Ad result does not automatically mean there is a broken bone chain.²

Type B: The Flat Trace

A Type B tympanogram is essentially flat, with no identifiable peak. The eardrum is not moving normally at any pressure point during the sweep. This is the pattern most closely associated with fluid behind the eardrum (middle ear effusion), particularly in children with otitis media with effusion. One study comparing Type B tympanograms with surgical findings at myringotomy reported a sensitivity of about 86% and a positive predictive value around 94%, meaning that when the test showed a flat trace with normal canal volume, fluid was almost always confirmed surgically.³

But here is the critical detail that separates a useful reading from a misleading one: you cannot interpret a Type B tympanogram without also looking at the ear canal volume (often abbreviated ECV or Veq). That single number, printed alongside the curve, changes the meaning of the flat trace entirely.

Flat Trace With Normal Canal Volume

When the canal volume falls within normal limits and the trace is flat, the most likely explanation is fluid or thick mucus filling the middle ear space. In children, normal ear canal volume typically ranges from about 0.3 to 1.0 mL, and in adults from roughly 0.65 to 1.75 mL.⁴ A flat trace paired with a volume in these ranges points strongly toward middle ear effusion, since the intact eardrum is simply being prevented from moving by the fluid behind it. That said, false positives do occur. The study mentioned above noted that clinical findings and additional audiological tests should factor into the final decision about management, because a small number of flat tympanograms turn out not to have fluid at surgery.

Flat Trace With Large Canal Volume

When the canal volume is abnormally large and the trace is flat, the probe is measuring a space that extends beyond the ear canal into the middle ear itself. This happens when the eardrum has a perforation or when a ventilation tube (grommet) is patent and open. The instrument reads one continuous air space rather than a sealed canal bouncing off an eardrum. In children with ventilation tubes, research has established cutoff values around 1.13 mL to distinguish a patent tube from a blocked one, with an increase of about 0.35 mL from baseline suggesting the tube is open.⁵ So a flat trace with a large volume is not alarming in a child with tubes; it actually means the tube is doing its job.

Type C: The Negative-Pressure Shift

A Type C tympanogram has a recognizable peak, but it is shifted to the left, into the negative pressure zone. This means the air pressure inside the middle ear is lower than atmospheric. The usual explanation is that the eustachian tube is not ventilating the middle ear properly, so the existing air gets absorbed by the mucosa and a partial vacuum develops. An expert consensus statement on eustachian tube dysfunction agreed that a tympanogram showing negative middle ear pressure, combined with patient-reported symptoms, is key evidence for diagnosing the dilatory form of the condition.⁶

The degree of the shift matters. Mild negative pressure (around -50 to -100 daPa) can be a transient finding, seen during a cold or allergy flare-up, and may resolve on its own. More extreme shifts (beyond -200 daPa) suggest sustained eustachian tube trouble and raise the question of whether fluid is starting to accumulate. A persistent Type C pattern in a child is sometimes considered a warning that the ear is heading toward a full effusion.

There is also an interesting wrinkle. Some Type C tympanograms are not caused by negative middle ear pressure at all. A contraction of the tensor tympani muscle during the test can pull the eardrum inward and mimic a negative-pressure peak, even when the middle ear pressure is actually normal. This has been documented as a persistent finding in some individuals, where swallowing and opening the eustachian tube fails to shift the peak back toward zero because the problem was never truly a pressure deficit.⁷ Clinicians who see an unexpectedly stubborn Type C result should keep this possibility in mind.

Tympanometric Width and Gradient

Beyond the Jerger classification (Types A, B, C), many tympanometry printouts include a measurement of how broad or narrow the peak is. This is called tympanometric width (TW) or gradient, and it adds resolution that the letter classification alone can miss. A narrow, sharply peaked curve suggests a healthy, air-filled middle ear. A wide, rounded peak suggests that some fluid or thickened mucosa is present, even though the curve technically still has a peak and might be labeled Type A or C.

This turns out to be genuinely useful. MRI-validated research has confirmed that tympanometric width correlates well with the actual amount of fluid present in the middle ear, giving it high predictive value for diagnosing effusion.⁸ A separate MRI study found that all three common methods of calculating gradient (width, difference, and ratio) correlated with fluid quantity, though the width method tended to perform slightly better.⁹ In pediatric screening programs, a tympanometric width cutoff is often used as the pass/fail criterion alongside peak pressure, because it catches borderline cases that a simple A/B/C label might miss.

Why Standard Tympanometry Fails in Young Infants

If you are reading a tympanogram on a baby under about six months old, everything above needs a significant caveat. The standard 226 Hz probe tone that works well in older children and adults produces unreliable results in young infants because their ear canal walls are soft and compliant. The canal itself absorbs and distorts the signal, so a baby with a fluid-filled middle ear can still produce what looks like a normal tympanogram.

The solution is high-frequency tympanometry using a 1000 Hz probe tone, which is now recommended for infants from birth through about six months of age.¹⁰ The difference in accuracy is dramatic. When compared against surgical findings, the 1000 Hz probe detected middle ear effusion with a sensitivity of 97-98%, while the standard 226 Hz probe managed only 43-61% sensitivity in the same infants.¹¹ In other words, the standard test missed roughly half the ears that actually had fluid. If a newborn hearing screening program flags a baby and the follow-up uses 226 Hz tympanometry, a “normal” result should be treated with real skepticism.

Reading a 1000 Hz tympanogram looks a bit different. Instead of the single smooth peak of a 226 Hz trace, you may see a broader or multi-peaked pattern. Clinicians look for whether a recognizable peak is present at all and whether it falls within age-appropriate norms, rather than applying the standard adult Type A/B/C framework directly. Earlier work using susceptance tympanograms and ipsilateral acoustic reflex thresholds in infants under five months showed excellent agreement with otoscopic findings, supporting the idea that higher-frequency approaches are the right tool in this age group.¹²

How Accurate Is Tympanometry Overall

Tympanometry is a screening and diagnostic aid, not a standalone gold standard. Its accuracy for detecting middle ear effusion has been evaluated in multiple studies comparing the tympanogram result against what surgeons actually find when they open the eardrum. The numbers are consistently good but not perfect. One study found sensitivity of 90% and specificity of 86% when compared with myringotomy findings in children.¹³ Another reported sensitivity of 88% and specificity of 71%.¹⁴ A third study found no significant difference in predictive accuracy between tympanometry (89%) and pneumatic otoscopy (88%), and combining the two did not meaningfully improve the result.¹⁵

What this means practically is that tympanometry is about as good as a skilled clinician looking through an otoscope, and the two methods tend to agree. The test’s real advantage is objectivity: it produces a printed result that does not depend on the examiner’s experience, lighting conditions, or how cooperative a squirming toddler is. Its weakness is that it tells you about pressure and compliance at a single frequency, which sometimes misses subtle pathology or, in the infant scenario described above, gives outright misleading results.

Screening Referral Rates in Children

If your child comes home from school with a note saying they failed a tympanometry screening, it helps to know what the referral thresholds actually mean. Current guidelines from major audiology organizations set fairly conservative pass/fail criteria, which leads to high referral rates in younger children. In five- to seven-year-olds, about 12-13% of children are referred using standard guidelines.¹⁶ The rate drops substantially by ages six to seven, falling to around 3%. Many of these referrals turn out to be transient issues, such as a resolving cold causing mild eustachian tube congestion. A failed screening is a reason to follow up, not a reason to panic.

Wideband Absorbance and the Future of the Test

Standard tympanometry uses a single probe tone, usually 226 Hz, which gives you one slice of the middle ear’s behavior. A newer approach called wideband absorbance (or wideband acoustic immittance) sweeps a broad range of frequencies simultaneously, producing a three-dimensional picture of how the middle ear handles sound energy across the entire speech-relevant spectrum. This is a meaningful upgrade because different pathologies leave distinct fingerprints across frequencies in ways that a single-frequency tympanogram cannot capture.

For detecting middle ear effusion, averaging absorbance across 500, 1000, and 2000 Hz has been shown to outperform both standard 226 Hz and 1000 Hz compliance tests.¹⁷ Wideband absorbance can also reliably distinguish between ears with effusion and ears with eardrum perforations, two conditions that look similar on a standard flat tympanogram but have very different clinical implications.¹⁸

Wideband testing is not yet available in every clinic, but it is gradually becoming standard in research settings and specialty audiology practices. For routine screening, the classic 226 Hz tympanogram remains perfectly adequate. Where wideband testing earns its keep is in ambiguous cases, in infant assessment, and in pre- and post-surgical monitoring.

Tympanometry After Ear Surgery

Tympanograms are commonly used to track outcomes after middle ear procedures such as stapedotomy (the surgery for otosclerosis, where the stapes bone is replaced with a prosthesis). Before surgery, ears with otosclerosis show very low energy absorbance across middle frequencies, sometimes below 10%, because the stiffened stapes blocks sound energy from entering the middle ear normally. After surgery, absorbance values improve and the characteristic low-frequency dip disappears, though research using wideband absorbance has shown that even after successful surgery, the middle ear system does not fully return to normal.¹⁹ The improvement is real and hearing gets better, but the tympanometric signature remains subtly different from a healthy ear that was never affected. Knowing this prevents false concern if a post-surgical follow-up tympanogram does not look completely textbook.

Tympanometry and Diving

Outside the audiology clinic, tympanometry has a practical application for recreational and professional divers. Descending underwater increases pressure on the eardrum, and if the eustachian tube cannot equalize fast enough, the result is middle ear barotrauma, ranging from discomfort to eardrum rupture. Tympanometric testing before and after dives has shown that middle ear pressures decrease in proportion to diving frequency, reflecting eustachian tube dysfunction that typically resolves once the person stops diving.²⁰

More interestingly, pre-dive tympanometric testing can predict who is likely to get barotrauma. A multi-step eustachian tube function test combined with imaging of the mastoid bone achieved a positive predictive value of 86% for subsequent barotrauma when both tests were positive.²¹ For divers who repeatedly struggle with ear clearing, a tympanometric evaluation can help determine whether the problem is anatomical and worth investigating further, or whether it is more likely to improve with technique adjustments and decongestants.