The graph

Across the bottom run the frequencies, from low (125 or 250 Hz, a deep hum) to high (8000 Hz, a hiss). Down the side runs hearing level in decibels: 0 dB HL at the top is the average threshold of young adults with normal hearing, and the scale goes down the page as hearing gets worse. Each point on the graph is the quietest tone you could just detect at that frequency. Lower on the page means louder was needed.

Roughly: 0–20 dB is normal; 21–40 mild; 41–70 moderate; 71–90 severe; over 90 profound. Conversational speech sits around 50–65 dB, spread across 250–4000 Hz, with the consonants that make words intelligible concentrated in the higher frequencies at lower levels.

Two ears, two lines each

Each ear is tested twice. Air conduction (circles for the right ear, crosses for the left) is measured through headphones or inserts: sound passes through the whole system — canal, drum, ossicles, cochlea, nerve. Bone conduction (brackets or arrows) uses a vibrator on the bone behind the ear: sound bypasses the outer and middle ear and reaches the cochlea directly.

The difference between them is the air-bone gap.

Air and bone the same, both normal: normal hearing.
Air and bone the same, both reduced: sensorineural loss — the problem is in the inner ear or nerve.
Air worse than bone, bone normal: conductive loss — the problem is in the outer or middle ear, and the inner ear is fine.
Air worse than bone, bone also reduced: mixed loss.

Masking

Sound presented to one ear reaches the other through the skull. To be sure which ear is responding, the audiologist puts a noise into the non-test ear. Poor masking creates false gaps and false symmetry; it is the commonest reason an audiogram misleads, and the first thing to check when the picture does not fit.

Reading the fine print

Note the transducer (supra-aural versus insert; inserts avoid collapsing canals and increase interaural attenuation). Check masked versus unmasked bone-conduction symbols. A Carhart notch at 2 kHz in an otherwise conductive picture suggests stapes fixation and partly reverses after successful surgery. A low-frequency gap with supranormal bone conduction (better than 0 dB) and present reflexes raises a third-window lesion. Pure-tone average is conventionally 500–1000–2000 Hz (sometimes with 3 or 4 kHz); for surgical outcome reporting, the air-bone gap should be calculated from post-operative air and post-operative bone, not pre-operative bone, to avoid flattering results through Carhart-notch recovery.

What the audiogram cannot tell you

An audiogram measures detection of pure tones in silence. It does not measure:

how well you understand words — speech audiometry does that;
how you cope with background noise — the commonest complaint, and the one pure tones predict worst;
whether your two ears work together — binaural hearing;
where sound comes from — spatial hearing;
how tiring listening is — listening effort.

Two people with nearly identical audiograms can have very different hearing lives. That is not a reason to distrust the audiogram; it is a reason to ask what else should be measured before a decision is made on the graph alone.

Beyond the audiogram

Thresholds
Speech
Noise
Space
Binaural function
Listening effort
Patient experience

An audiogram is part of the story — not the whole story.

This page provides general educational information. It cannot replace an individual assessment, which depends on a full history, examination, audiometry and, where relevant, imaging. If you have sudden hearing loss, severe pain, facial weakness, severe dizziness or discharge with fever, seek medical care promptly.