How to Read an Audiogram: A Plain-Language Guide for WHS Managers

An audiogram is a graph that represents a person’s hearing. It’s the central document in audiometric testing, yet many WHS managers and HR professionals find it confusing. The axes are unfamiliar, the symbols are cryptic, and the threshold values feel abstract. This guide demystifies the audiogram so you can understand what the test results actually mean for your workplace.

By the end, you’ll be able to look at an audiogram and understand whether a worker’s hearing is normal, experiencing age-related loss, showing early noise-induced hearing loss, or something else entirely.

What an Audiogram Is

An audiogram is a graphical representation of hearing thresholds across different frequencies. It answers a simple question: “What is the quietest sound the person can hear at each frequency?”

The result is plotted on a grid with:

X-axis (horizontal): Frequency (pitch) of the sound, measured in Hertz (Hz)
Y-axis (vertical): Hearing level (loudness threshold), measured in decibels (dB HL)

Each point on the graph represents the threshold at that frequency. Connected points form a line showing the hearing profile across the frequency range.

The Y-Axis: Hearing Level (dB HL)

The Y-axis measures hearing level in dB HL (decibels Hearing Level). This is the key to understanding the graph:

0 dB HL: Normal hearing threshold (quietest sound a person with normal hearing can detect at that frequency)
Below 0 dB HL: Better than normal (rare; indicates someone with exceptionally good hearing)
Above 0 dB HL: Elevated threshold (hearing is worse than normal)
25 dB HL: Borderline (still considered “normal” in many contexts, but at the high end of normal)
40 dB HL: Mild hearing loss
60 dB HL: Moderate hearing loss
80+ dB HL: Severe hearing loss

Important convention: The Y-axis goes DOWNWARD. So as you move down the graph, thresholds worsen (higher dB HL values = poorer hearing). This is counterintuitive but standard in audiometry.

Example: A point at 40 dB HL is plotted lower on the graph than 20 dB HL, showing worse hearing (needing louder sound to detect).

The X-Axis: Frequency (Hz)

The X-axis shows frequency (pitch) in Hz, measured on a logarithmic scale:

250 Hz: Very low frequency (rumbling sounds)
500 Hz: Low frequency (bass notes, vowel sounds in speech)
1000 Hz: Mid frequency (reference frequency in many standards)
2000 Hz: Mid-high frequency
3000 Hz: Mid-high frequency
4000 Hz: High frequency (consonants in speech; classic NIHL indicator)
6000 Hz: High frequency
8000 Hz: Very high frequency (edge of speech perception)

Why these frequencies? They cover the range of human speech. Frequencies below 250 Hz and above 8000 Hz are less critical for everyday communication, so they’re not routinely tested in workplace audiometry.

Reading the Symbols

Audiograms use standardised symbols to represent different test conditions and ears:

O (circle): Right ear, air conduction
X (cross): Left ear, air conduction
< (less-than symbol): Right ear, bone conduction
> (greater-than symbol): Left ear, bone conduction

In a typical workplace audiogram, you’ll see O and X symbols (air conduction only). Bone conduction (< and >) is less common in routine workplace testing.

Example interpretation: If you see an O at 250 Hz with a threshold of 15 dB HL, this means the right ear’s air conduction threshold at 250 Hz is 15 dB HL.

Normal Hearing Range

Definition: Normal hearing is defined as thresholds of 0–25 dB HL at all frequencies tested.

0–20 dB HL: Clearly normal
21–25 dB HL: Within normal range but at the high end; some standards consider this borderline
26+ dB HL: Beyond normal; indicates mild hearing loss at that frequency

In workplace audiometric testing, a result with all thresholds ≤25 dB HL is typically categorised as “Normal” or “Pass,” and no referral is recommended.

The 4kHz Notch: The Signature of NIHL

One of the most important patterns in occupational audiometry is the 4kHz notch—a characteristic dip in the audiogram at 4000 Hz.

What It Looks Like

Imagine a normal audiogram where all frequencies are at 15 dB HL (normal). The 4kHz notch appears as a sudden drop, where 4kHz shows a threshold of, say, 35–40 dB HL, while adjacent frequencies (3kHz and 6kHz) are only mildly elevated (25–30 dB HL).

The result: a V-shaped or notch appearance at 4000 Hz.

Why 4kHz?

The 4kHz frequency is particularly vulnerable to noise exposure. The cochlea’s mechanical properties make the 4kHz region especially sensitive to noise damage. Almost all noise-induced hearing loss starts at 4kHz before spreading to adjacent frequencies.

The Pathognomonic Sign

“Pathognomonic” means uniquely characteristic of a disease. The 4kHz notch is the pathognomonic sign of noise-induced hearing loss. When you see it, NIHL is the most likely diagnosis.

Important caveat: Not all NIHL shows a 4kHz notch (severe cases may show a broader pattern), and not all 4kHz notches are purely from noise (certain medications and acoustic trauma can also cause similar patterns). But a clear 4kHz notch is the classic NIHL marker.

Recovery Pattern

Interestingly, in very early NIHL, the hearing sometimes recovers at 6kHz and 8kHz while remaining damaged at 4kHz. So you might see:

– 3kHz: 20 dB HL (near-normal)
– 4kHz: 40 dB HL (notch)
– 6kHz: 25 dB HL (recovering)
– 8kHz: 20 dB HL (recovered)

This pattern is pathognomonic for early noise exposure damage.

Bilateral vs Unilateral Hearing Loss

Bilateral Loss (Both Ears Affected)

If both the O (right ear) and X (left ear) lines are elevated and follow a similar pattern, this is bilateral hearing loss. This is typical for:

Noise-induced hearing loss (from occupational or recreational noise exposure affecting both ears)
Age-related hearing loss (presbycusis—affects both ears similarly)
Systemic conditions

Bilateral loss from occupational exposure is expected if both ears have been exposed equally.

Unilateral Loss (One Ear Affected)

If one ear (right or left) shows thresholds significantly worse than the other, this is unilateral loss. In workplace testing, unilateral loss is unusual and often indicates:

Asymmetric noise exposure (one ear more exposed—rare in typical workplaces)
Ear pathology (infection, wax impaction, ear disease)
Acoustic trauma in one ear (explosion, gunshot, impact in one ear only)
Something unrelated to occupational exposure

Significance: A unilateral finding warrants specialist referral to rule out non-occupational causes.

What a Significant Threshold Shift Looks Like

A “significant threshold shift” is defined as a change of 15 dB or more at any single frequency compared to the baseline audiogram (WHS Regulation 58, based on AS/NZS 1269).

Example:

Year 1 baseline at 4kHz: 20 dB HL (normal)
Year 2 retest at 4kHz: 37 dB HL (elevated)
Shift: 17 dB (exceeds the 15 dB threshold)
Significance: Significant threshold shift detected

When a significant threshold shift is detected, the employer must:

Review and potentially improve noise controls
Refer the worker for specialist assessment
Document the shift and control review in WHS records

Mild, Moderate, and Severe Loss Ranges

For quick classification of hearing loss severity, use these ranges (average across frequencies 500–3000 Hz, which are most important for speech):

0–25 dB HL: Normal hearing (no loss)
26–40 dB HL: Mild hearing loss
41–55 dB HL: Moderate hearing loss
56–70 dB HL: Moderately severe hearing loss
71–90 dB HL: Severe hearing loss
90+ dB HL: Profound hearing loss

Note: These are rough guides. Clinical classification can vary by standard and expert opinion.

Reading the Employer’s Group Report

As a WHS manager, you typically don’t receive individual audiograms. Instead, you get an employer summary report that categorises workers:

Normal: Number of workers with thresholds ≤25 dB HL at all frequencies. No action required.
Refer: Number of workers with thresholds >25 dB HL at any frequency OR significant threshold shift compared to baseline. These workers should be referred for specialist assessment.

The report may also show:

Comparison to baseline (if previous testing exists)
Number of significant threshold shifts detected
Recommendations for control review

What to Do When a Worker Gets a “Refer” Result

If testing results in a “Refer” categorisation, this is not a diagnosis of permanent hearing loss. It means further evaluation is recommended. The next steps are:

Specialist referral: Arrange for the worker to see an audiologist or ENT specialist
Specialist assessment: The specialist will conduct detailed testing and medical examination
Diagnosis: The specialist determines the cause and severity of any hearing changes
Recommendations: May include hearing aids, workplace modifications, additional monitoring, or work restrictions
WHS response: The employer uses specialist findings to improve controls and support the worker

The employer’s cost obligation: WHS law requires the employer to cover specialist referral costs as part of the audiometric testing program.

Frequently Asked Questions

Q1: What does it mean if one ear is worse than the other?

Unilateral loss (one ear significantly worse) warrants specialist referral. It may indicate ear pathology, asymmetric exposure, or non-occupational causes. Rare in typical occupational NIHL.

Q2: Can age-related hearing loss look like NIHL?

Age-related loss (presbycusis) shows a high-frequency sloping pattern (worse at 6–8kHz) across both ears symmetrically. NIHL typically shows a 4kHz notch. They look different, though both may be present in an older worker with both age and occupational exposure.

Q3: If my audiogram is normal this year but worse next year, what does that mean?

If thresholds worsen by 15 dB or more at any frequency, this is a significant threshold shift. It indicates deterioration, possibly from continued noise exposure. Control measures should be reviewed.

Q4: Can I have a 4kHz notch without occupational noise exposure?

Rarely. The 4kHz notch is highly specific to noise exposure. If present, it suggests noise exposure somewhere in the person’s history (occupational, recreational, or acoustic trauma).

Q5: What if my baseline audiogram shows mild loss? Does that mean I was damaged before hire?

Possibly, or it could reflect age, previous noise exposure, or genetics. The baseline establishes a reference point. As long as subsequent testing shows stable thresholds, it indicates controls are working.

Q6: Can temporary hearing loss be distinguished from permanent loss on an audiogram?

Not directly from a single audiogram. Temporary threshold shift resolves within 16–18 hours of quiet. If testing shows recovery on retest after adequate quiet, the shift was temporary. If thresholds remain elevated, it’s permanent.

Q7: What if my hearing is unusually good (thresholds -10 dB HL)?

Excellent hearing. This is rare but normal in some younger people. As you age, thresholds naturally worsen (presbycusis), so maintain good hearing health with protection.

Q8: How do I compare my current audiogram to my baseline?

Your testing provider should provide a comparison graph showing baseline and current results side-by-side. If thresholds at any frequency have worsened by 15+ dB, this is a significant shift requiring follow-up.