Understanding an audiogram

An audiogram is the chart used to record and display the results of a hearing test. It shows hearing levels in a consistent visual format, so clinicians can document results clearly and compare findings across different pitches.

At this stage, it is enough to understand that the audiogram is a graph. The next steps will explain what each axis means, why the scale looks unusual, and how results are added to the chart.

Frequency describes the pitch of a sound. It is measured in hertz, written as Hz. A higher number means a higher-pitched sound, and a lower number means a lower-pitched sound.

On an audiogram, frequency is shown across the horizontal axis. The lower frequencies are on the left, and the higher frequencies are on the right. Some frequencies are written in Hz, such as 250 Hz or 500 Hz. Others are often shortened into kHz, where 1 kHz means 1000 Hz.

At this stage, frequency should be understood as pitch, not loudness. Loudness or level is shown separately on the vertical axis.

Frequency increases as you move from left to right across the audiogram. Lower-pitched sounds are shown on the left side of the chart, and higher-pitched sounds are shown on the right.

The main frequencies commonly seen on an audiogram are 250 Hz, 500 Hz, 1 kHz, 2 kHz, 4 kHz and 8 kHz. Some audiograms also include intermediate frequencies, such as 750 Hz, 1.5 kHz, 3 kHz and 6 kHz, which provide more detail between the main test points.

A helpful visual analogy is the colour spectrum: lower frequencies can be thought of like the red end, while higher frequencies can be thought of like the blue or violet end. This is only a visual analogy to help understand the direction of increasing frequency.

Intensity describes the level of the test sound. On an audiogram, this is shown on the vertical axis and is measured in dB HL, which means decibels hearing level.

dB HL is different from dBA. dBA is commonly used when measuring environmental or workplace noise, while dB HL is used in hearing testing. dB HL compares hearing thresholds against an expected hearing reference level, which is why an audiogram can show values such as 0 dB HL or even -10 dB HL. These values do not mean there is no sound; they belong to a hearing-level scale.

The audiogram can feel upside down at first. Softer sounds are shown near the top of the graph, and louder sounds are shown lower down. This means that a mark lower on the audiogram usually means the sound had to be made louder before the person responded.

0 dB HL is an important reference line on the audiogram. It does not mean silence. Instead, it represents the hearing-level reference point used when recording hearing thresholds.

This line helps clinicians quickly judge how far a threshold sits from the expected reference area. Results close to 0 dB HL are near the top of the audiogram, while results further down the chart show that the sound needed to be made louder before the patient responded.

At this stage, the main thing to remember is that 0 dB HL is a comparison point. It helps make the audiogram easier to read once thresholds are plotted.

Audiograms are often described using broad severity terms. These terms help summarise how far hearing thresholds sit from the expected hearing range.

These descriptions are useful, but they are only a summary. They do not replace looking at the full shape of the audiogram, the frequencies affected, or whether one ear differs from the other.

A threshold is the softest level where a person gives a reliable response to a test sound at a specific frequency.

On the audiogram, each plotted point represents a threshold. It does not show every sound the patient heard during the test. Instead, it shows the lowest reliable level recorded for that frequency.

For example, if a point is plotted at 1 kHz and 30 dB HL, this means the person’s threshold at 1 kHz was 30 dB HL. In other words, that was the softest reliable response obtained for that pitch.

Air-conduction results show hearing thresholds measured through the ear canal, usually using headphones or insert earphones.

On a standard audiogram, right-ear air-conduction thresholds are usually shown using red circles. Each red circle marks the right-ear threshold at one frequency.

When several right-ear thresholds are plotted, the red circles are usually joined with a continuous line. This helps show the pattern of hearing across the frequencies tested.

On a standard audiogram, left-ear air-conduction thresholds are usually shown using blue crosses. Each blue cross marks the left-ear threshold at one frequency.

Like the right-ear air-conduction results, the left-ear symbols are usually joined with a continuous line. This helps show the pattern of hearing across the frequencies tested in the left ear.

At this stage, the key point is that blue crosses belong to the left ear and show air-conduction results.

Bone-conduction results show hearing thresholds measured through a bone vibrator rather than through earphones. These results help clinicians understand how the cochlea responds when sound reaches it through vibration of the skull, rather than through the outer and middle ear.

Bone-conduction thresholds are recorded using green triangle symbols. They are commonly plotted at 500 Hz, 1 kHz and 2 kHz, with additional frequencies added when needed.

Bone-conduction results are important because they can be compared with air-conduction results. This comparison helps clinicians identify whether hearing thresholds are being affected by the outer or middle ear, the inner ear, or a combination of both. Later lessons will explain this in more detail when air-bone gaps and masking are introduced.

Once thresholds are plotted, the audiogram starts to show a pattern. Clinicians look at where the points sit on the graph and how they change across frequency.

The pattern can show whether hearing levels are similar across pitches, whether hearing becomes poorer in the higher frequencies, whether one ear is different from the other, and whether air-conduction and bone-conduction results appear close together or separated.

At this stage, the aim is not to fully diagnose the type of hearing loss. The key idea is that the shape of the audiogram gives useful clinical information, and this is why thresholds are plotted across several frequencies rather than at just one pitch.

Once the audiogram has been fully plotted, clinicians can begin to describe the result in a clear and structured way.

A useful explanation often includes three parts: the degree of hearing loss, such as mild, moderate, severe or profound; the type of hearing loss, such as conductive, sensorineural or mixed; and the shape or pattern of the hearing loss across frequency.

For example, if the air-conduction and bone-conduction results are both raised and sit close together, the result may be described as sensorineural. If the thresholds sit mainly within the mild and moderate ranges, a clinician might describe this as a mild to moderate sensorineural hearing loss.

The full audiogram still matters. A short phrase such as “mild to moderate sensorineural hearing loss” is useful, but it does not describe every detail. Clinicians should also consider whether the loss affects one or both ears, whether it is worse in the high frequencies, and whether the patient’s symptoms match the test results.