How to Read a Military Audiogram

If you have served in the Army, Royal Navy, Royal Marines or Royal Air Force, you may have several audiograms in your service medical records. They might have been taken when you joined, during routine hearing surveillance, after a noise incident or before leaving service.

At first glance, the graph can look complicated: numbers across the top, decibels down the side, circles, crosses, lines and sometimes brackets or arrows. The basic idea is much simpler — an audiogram records the quietest sound you could hear at different pitches in each ear.

This guide explains how to understand the chart without turning it into a self-diagnosis tool.

The short version

• The horizontal axis shows frequency, measured in hertz (Hz).
• Low-pitched sounds are on the left; high-pitched sounds are on the right.
• The vertical axis shows hearing level, usually in decibels hearing level (dB HL).
• Results near the top of the graph generally represent better hearing.
• Results further down mean the sound had to be louder before you detected it.
• A circle usually represents the right ear during air-conduction testing.
• A cross usually represents the left ear.
• Bone-conduction symbols help clinicians distinguish different types of hearing loss.
• Military hearing records should ideally be looked at as a series, not one isolated test.
• A 4 kHz notch may be relevant to noise exposure, but it is not a yes/no test for military NIHL.
• 6 kHz and 8 kHz can be particularly important in military hearing cases.
• Some older military audiograms did not test 8 kHz.
• An audiogram does not prove whether the MOD caused your hearing loss.
• A modern diagnostic audiogram conducted to appropriate standards is generally stronger evidence than a screening test, but historic service audiograms can still be important.

What is an audiogram?

An audiogram is the graph produced by pure-tone audiometry.

During the test, tones at different pitches are played through headphones or insert earphones.

You normally press a button or otherwise respond when you hear a tone.

The tester changes the volume until they identify the quietest level at which you can reliably detect that frequency. That point is your hearing threshold.

The process is repeated at several frequencies and usually for both ears. The results are then plotted on the audiogram.

The British Society of Audiology describes pure-tone audiometry as the standard method for measuring hearing thresholds across a range of frequencies. Audiograms are used to assess the degree, pattern and type of hearing loss.

What does the horizontal axis mean?

The horizontal axis represents frequency, measured in hertz, abbreviated to Hz. Frequency describes the pitch of a sound.

As you move across the audiogram from left to right: low frequency → high frequency.

Typical frequencies may include:

• 250 Hz
• 500 Hz
• 1,000 Hz
• 2,000 Hz
• 3,000 Hz
• 4,000 Hz
• 6,000 Hz
• 8,000 Hz

1,000 Hz may also be written as 1 kHz, because one kilohertz equals 1,000 hertz. Similarly 2 kHz = 2,000 Hz, 4 kHz = 4,000 Hz, 6 kHz = 6,000 Hz and 8 kHz = 8,000 Hz.

What do low and high frequencies sound like?

Lower frequencies correspond broadly to deeper-pitched sounds. Higher frequencies correspond broadly to sharper or higher-pitched sounds.

Speech contains information across a range of frequencies. Vowel sounds contain substantial lower-frequency energy, while many consonants that help distinguish one word from another contain important higher-frequency information.

That is one reason somebody with high-frequency hearing loss may say: "I can hear people talking, but I cannot always understand the words." They may hear the overall voice but lose some of the detail that makes speech clear.

What does the vertical axis mean?

The vertical axis records hearing level, normally measured in dB HL, which means decibels hearing level.

The scale works in a direction that can initially seem backwards. At the top of an audiogram are softer test levels. As you move down the graph, the tones become louder.

So higher on the page generally = better threshold, and lower on the page generally = poorer threshold.

If your threshold at 4 kHz is plotted at 10 dB HL, you detected a relatively soft tone. If it is plotted at 60 dB HL, the tone had to be made considerably louder before you detected it.

Does 0 dB mean complete silence?

No. This is an important misunderstanding.

0 dB HL does not mean that no sound exists.

The hearing-level scale is calibrated around reference hearing thresholds. A result around 0 dB HL means the listener can detect a tone at approximately the reference level used for people with good hearing at that frequency.

It is therefore possible for somebody to record a threshold slightly better than 0 dB HL, such as -5 dB HL. That does not mean they can hear "less than silence".

What does a plotted point actually mean?

Each plotted point represents a hearing threshold at a particular frequency.

For example, Right ear: 4 kHz = 35 dB HL means that during that test the quietest 4 kHz tone reliably detected by the right ear was approximately 35 dB HL.

It does not mean:

• that the person has lost exactly 35% of their hearing;
• that every sound must be 35 dB louder;
• that they have 35 dB of military hearing loss;
• or that the MOD caused 35 dB of damage.

The number is a threshold measurement, not a percentage of hearing or a legal calculation.

Which symbol is which ear?

On a conventional audiogram, unmasked air-conduction results usually use O = right ear and X = left ear.

So if you see a line of circles across the graph, those results normally represent the right ear. A line of crosses normally represents the left ear.

Some audiograms also use colours — red = right, blue = left — but colour should never be relied upon by itself, particularly on photocopied or scanned military records. The symbol key on the actual audiogram is more important.

The British Society of Audiology also notes that computerised systems may use different symbols, provided the results remain clear and unambiguous.

What is air conduction?

Air-conduction testing is the familiar part of a hearing test where tones are played through headphones or insert earphones.

The sound travels through:

• the ear canal;
• the eardrum;
• the middle-ear bones;
• the inner ear;
• and then the auditory pathway.

Air-conduction thresholds therefore reflect the performance of the hearing system as a whole. The usual unmasked symbols are O for the right ear and X for the left.

What is bone conduction?

A diagnostic hearing assessment may also test bone conduction. Instead of playing the tone through an earphone, the audiologist places a small vibrating device against the skull, usually behind the ear.

The vibration allows sound energy to reach the inner ear while substantially bypassing the outer and middle ear.

Comparing air- and bone-conduction thresholds helps the audiologist determine what type of hearing loss may be present. For example, it can help distinguish:

• conductive hearing loss;
• sensorineural hearing loss;
• mixed hearing loss.

Bone-conduction results use different symbols from the circles and crosses used for ordinary air-conduction testing. You do not need to memorise every symbol — the audiogram should contain a key.

What is an air-bone gap?

An air-bone gap occurs where the air-conduction threshold is poorer than the corresponding bone-conduction threshold.

In simple terms, the inner ear may be responding better than the complete air-conduction pathway. That can indicate a conductive component to the hearing loss, involving the outer or middle ear.

Possible examples of conductive problems include certain forms of:

• middle-ear disease;
• eardrum problems;
• obstruction;
• or other conditions preventing sound travelling normally through the outer or middle ear.

Noise-induced hearing loss is generally a sensorineural condition. That is one reason bone-conduction testing can be important when somebody's hearing loss needs to be properly diagnosed rather than merely screened.

What does "masked" mean on an audiogram?

Sometimes it is difficult to be certain that the ear being tested is the ear that actually detected the sound.

If a sufficiently loud tone is played into one ear, sound energy can potentially reach the opposite cochlea. This is called cross-hearing.

Audiologists can use masking to deal with this. A masking noise is presented to the ear that is not being tested while the audiologist measures the threshold of the test ear. This helps isolate the ear under examination.

Masked thresholds use different symbols on the audiogram. The exact symbols matter much less to a patient than understanding the principle: masking helps the audiologist be more confident that the plotted threshold genuinely belongs to the ear being tested.

What does an arrow next to a symbol mean?

An arrow attached to an audiogram symbol can indicate no response at the maximum output available from the audiometer at that frequency.

It does not mean the person's threshold was measured at the point shown. It means their true threshold may be worse than the maximum level the equipment could test.

The British Society of Audiology recommends that no-response symbols should not simply be connected into the ordinary threshold line as if they were measured thresholds.

What frequencies are used in military hearing tests?

Military hearing surveillance has used a range of frequencies.

Current and historic MOD material describes hearing acuity being assessed using frequencies including:

• 500 Hz;
• 1 kHz;
• 2 kHz;
• 3 kHz;
• 4 kHz;
• 6 kHz.

The military hearing category traditionally separates these into a lower-frequency group of 500 Hz + 1 kHz + 2 kHz, and a higher-frequency group of 3 kHz + 4 kHz + 6 kHz.

Other military audiometry can include 250 Hz and 8 kHz as well.

Why is 8 kHz important?

8 kHz is a high-frequency measurement.

It became particularly important in the Abbott litigation because military NIHL does not always produce the exact audiometric pattern expected from traditional industrial-noise models.

Some historic MOD screening audiograms did not record 8 kHz. That means an old service audiogram may contain useful information at 3, 4 and 6 kHz but say nothing about the person's threshold at 8 kHz.

That missing information should not be invented.

In one of the Abbott test cases, the Court specifically rejected an attempt to reconstruct missing historic 8 kHz results by assuming what they must have been from a much later audiogram.

Why does 6 kHz matter?

6 kHz can also be important in noise-exposure cases. Noise-related changes do not always peak neatly at 4 kHz.

Military exposure may involve very intense impulse noise, including weapons and blast, and high-frequency changes at 6 kHz or 8 kHz can sometimes be relevant to the overall pattern.

But individual 6 kHz measurements may also require careful interpretation because audiometry at that frequency has historically presented technical and calibration issues with some equipment. Abbott considered this subject in considerable detail.

The practical point for a veteran is not to assume that "my 6 kHz result is bad, therefore I have military NIHL." It has to be interpreted in context.

What is a 4 kHz notch?

A notch is a shape on an audiogram. The thresholds become poorer across part of the higher-frequency range and then improve again at a higher frequency.

Traditional occupational NIHL is often associated with a notch centred around approximately 4 kHz.

For example, somebody might have:

• relatively good hearing at 1 kHz;
• relatively good hearing at 2 kHz;
• poorer hearing at 4 kHz;
• some recovery at 8 kHz.

Plotted on an audiogram, that can create a notch-shaped pattern.

Does a 4 kHz notch prove noise-induced hearing loss?

No.

A notch can support a diagnosis when considered with the rest of the evidence. But it is not unique to NIHL.

Likewise: no obvious 4 kHz notch does not automatically mean there is no military NIHL.

This point was central to [Abbott v Ministry of Defence [2026] EWHC 941 (KB)](/cases/abbott-v-mod-2026/). The Court concluded that the older CLB approach is not generally suitable for military NIHL and preferred the military-specific rM-NIHL method.

Our guide to what rM-NIHL is explains that method separately.

Why can a notch disappear on later audiograms?

An audiogram is a snapshot of hearing thresholds at a particular time.

Suppose somebody has a dip around 4 kHz when they are younger. Years later, their hearing at neighbouring higher frequencies may also become poorer because of ageing or another cause. The original dip can therefore become less visually obvious.

In Abbott, expert evidence addressed the fact that notches or "bulges" seen on serial audiometry can become less distinct as hearing at 6 and 8 kHz worsens.

So the absence of an obvious notch on a modern audiogram does not necessarily tell you what an earlier audiogram looked like. That is another reason serial audiograms matter.

Why are several audiograms better than one?

A single audiogram tells you what was recorded on one day. A series may show a pattern over years.

That hypothetical series may tell a clinician much more than looking only at the 2003 result.

But the opposite can also happen. One test might show an unexpectedly poor result while tests immediately before and afterwards are substantially better. That may prompt questions about whether the isolated test was reliable.

Abbott concluded that military screening audiograms can provide useful evidence, particularly where they demonstrate a consistent pattern across a series.

Are military audiograms reliable?

They should not automatically be accepted as perfect. They should not automatically be dismissed either.

This issue was examined directly in Abbott. Mr Justice Garnham concluded that:

• BSA-compliant diagnostic pure-tone audiometry is the gold standard and should be used as the best audiometric evidence in medico-legal cases when available;
• military screening audiograms are ordinarily suitable for screening and triage;
• consistent military audiograms can also assist diagnosis and quantification as part of clinical judgement;
• a series can help show hearing profiles and trends;
• unexplained variation can reduce confidence;
• audiometric evidence should be considered as a whole rather than in isolation;
• most MOD audiograms were conducted properly and in good faith, while recognising that errors or operational problems can occur.

That is a much more useful position than either "MOD hearing tests cannot be trusted" or "the MOD audiogram must be correct." Neither extreme reflects the judgment.

What can affect the reliability of an audiogram?

Possible factors include:

• testing environment;
• background noise;
• calibration of equipment;
• correct placement of headphones;
• the person's understanding of the test;
• concentration;
• fatigue;
• tinnitus;
• temporary hearing changes;
• tester technique;
• whether appropriate masking was performed;
• equipment limitations.

The BSA recommended procedure includes requirements concerning equipment checks, calibration, testing environment and recording of information about the audiometer and tester.

What if one military audiogram is very different from all the others?

Do not automatically choose the result that helps your preferred conclusion.

A clinician may ask whether the result is a genuine change or an outlier. The surrounding series matters.

For example, if a person has 10 dB → 10 dB → 55 dB → 10 dB at the same frequency over a relatively short period, the isolated 55 dB result may require investigation.

But if the sequence is 10 dB → 20 dB → 35 dB → 50 dB, that presents a different pattern.

That does not establish the cause of the change, but the trend itself may be medically relevant.

What does H1, H2, H3 or H4 mean?

Some military records contain a hearing category rather than simply displaying the raw audiogram.

The military PULHHEEMS system includes an "H" component for hearing. The right and left ears can be assessed separately.

Public MOD/IMEG material describes categories including:

• H1 — good hearing
• H2 — acceptable hearing
• H3 — impaired hearing
• H4 — poor hearing, with continuing military employment requiring specialist consideration

Historic versions of the system have also used H8 where poor hearing was assessed as incompatible with continued service.

The category is calculated using grouped audiometric thresholds rather than simply reading one single frequency.

Does H1 mean I definitely had no military noise damage?

No.

A military hearing category serves an occupational and medical-employability purpose. It is not itself a medico-legal diagnosis of whether any degree of military NIHL existed.

IMEG has expressly noted that hearing acuity categories do not necessarily correlate closely with functional hearing ability.

And because the category uses grouped frequencies, an overall H grade can conceal detail visible on the underlying audiogram. Where available, the actual threshold values are therefore much more informative than the category alone.

Does H3 or H4 prove military noise caused my hearing loss?

No. It tells you something about the level of measured hearing acuity. It does not tell you the cause.

A person could have impaired hearing because of:

• military noise;
• civilian occupational noise;
• ageing;
• ear disease;
• another medical condition;
• trauma;
• medication;
• or a combination of causes.

Causation requires more than the H category.

What is "hearing threshold shift"?

A threshold shift means hearing thresholds have changed between tests.

For example, 1998 at 4 kHz: 10 dB HL; 2002 at 4 kHz: 30 dB HL. That represents a 20 dB deterioration in the measured threshold at that frequency.

A change between two tests does not necessarily prove permanent hearing damage. The result may need repeating and considering with the wider record.

MOD hearing-surveillance policy is designed in part to identify threshold changes over time so that appropriate follow-up can occur.

What is a temporary threshold shift?

After loud noise exposure, hearing can temporarily become poorer. This is known as a temporary threshold shift, or TTS.

Someone might experience:

• muffled hearing;
• temporary dullness;
• tinnitus;
• reduced hearing sensitivity.

A later test may improve. That is different from a permanent threshold shift caused by permanent hearing injury.

If somebody was tested very soon after significant noise exposure, the timing of the test may therefore be relevant.

Can an audiogram show tinnitus?

No. Tinnitus is not a line on an audiogram.

An audiogram measures hearing thresholds. Tinnitus is the perception of sound without a corresponding external source.

Somebody can:

• have NIHL and tinnitus;
• have hearing loss without tinnitus;
• report tinnitus with relatively good conventional hearing thresholds.

An audiogram may provide relevant background information, but it cannot objectively prove whether somebody experiences tinnitus.

Can an audiogram show difficulty hearing speech in noise?

Not completely.

Pure-tone audiometry asks a relatively simple question: What is the quietest pure tone you can detect at this frequency?

Real-world listening is much more complicated. Somebody may perform reasonably on pure-tone testing but still report substantial difficulty:

• in pubs;
• restaurants;
• group conversations;
• vehicles;
• meetings;
• or other environments with background noise.

The British Society of Audiology specifically warns that pure-tone descriptors alone should not be treated as a reliable measure of communication difficulty in background noise.

Other forms of audiological testing may be appropriate where speech understanding is a particular concern.

What do "mild", "moderate", "severe" and "profound" mean?

Audiology reports sometimes summarise hearing thresholds using broad descriptors.

Current BSA guidance describes five-frequency average hearing thresholds as:

• mild: 21–40 dB HL;
• moderate: 41–70 dB HL;
• severe: 71–95 dB HL;
• profound: over 95 dB HL.

These are useful summaries. They are not complete descriptions of somebody's hearing.

The BSA itself warns that an average can hide the shape of hearing loss and should not be the sole measure of the communication difficulty somebody experiences.

For example, two people can have the same average threshold while having very different high-frequency hearing.

Can I calculate my percentage hearing loss from an audiogram?

Not reliably by simply turning the decibel numbers into percentages.

A threshold of 40 dB HL does not mean 40% hearing loss.

Different medical, compensation and legal systems may use particular calculations or averaging methods for particular purposes. Those calculations should not be confused with the audiogram itself.

The raw audiogram records thresholds.

Can an audiogram prove military NIHL?

No. This is the most important limitation of the entire page.

An audiogram can provide evidence consistent with NIHL. It can also provide evidence against a proposed diagnosis.

But there is no audiogram pattern that simply prints: "This hearing loss was caused by military service."

Abbott emphasised that NIHL diagnosis requires clinical judgement. Diagnostic methods such as rM-NIHL provide guidance, but they do not replace consideration of the individual history and evidence.

Relevant information can include:

• the audiometric pattern;
• serial service audiograms;
• modern diagnostic audiometry;
• age;
• military noise history;
• duration and intensity of exposure;
• hearing protection;
• civilian occupational exposure;
• recreational noise;
• tinnitus history;
• medical conditions;
• medication;
• ear disease;
• other possible causes.

Can I look at my audiogram and use rM-NIHL myself?

You may be able to understand the numbers. That does not mean you can reliably diagnose yourself.

The High Court's decision in Abbott did not convert rM-NIHL into a public eligibility calculator. The method is an aid to clinical diagnosis and has limitations.

Our dedicated guide to what rM-NIHL is explains how the method works, why it was preferred in Abbott and — most importantly — what it cannot establish by itself.

What if my old audiogram says I had normal hearing?

It matters. But the effect depends on the evidence.

Questions may include:

• when the test took place;
• which frequencies were recorded;
• whether 8 kHz was included;
• whether other service audiograms show the same pattern;
• whether the result fits later tests;
• whether the alleged harmful exposure occurred before or after the test;
• whether there is another explanation for later hearing loss.

Abbott demonstrates that consistent historic audiograms can be powerful contemporaneous evidence. They cannot simply be ignored because a later audiogram is abnormal.

What if my old audiogram was abnormal?

That also matters. But again, it does not answer causation by itself.

A clinician still needs to consider:

• the pattern of hearing loss;
• earlier tests;
• later tests;
• medical history;
• exposure history;
• other possible causes;
• and the reliability of the particular result.

What if I cannot find my old military audiograms?

Do not assume they never existed.

Historic service medical records may contain:

• audiogram graphs;
• numerical hearing results;
• medical examination forms;
• PULHHEEMS categories;
• hearing-surveillance records;
• ENT referrals;
• records following acoustic trauma.

Our forthcoming guide to military medical and hearing records will explain what records may exist and how veterans can request relevant information.

Should I upload my audiogram to an online tool?

Be cautious.

An online tool may help display threshold values or explain basic terminology. It should not be treated as a substitute for:

• clinical diagnosis;
• proper audiology;
• ENT assessment where required;
• or expert evidence in a legal claim.

This is especially important in military NIHL, where the High Court has already examined in detail why diagnosis requires more than a pattern-matching exercise.

When should I seek medical help rather than interpret the chart myself?

If your hearing has changed suddenly or rapidly, do not spend time analysing old military graphs to decide whether noise caused it. Seek healthcare.

Frequently asked questions