How Your Hearing Works (And What Happens When It Doesn't)
- Mark Ashmore
- Mar 9
- 10 min read
By Mark Ashmore, RHAD, MIOA, HCPC Registered Audiologist | Hear 4 The Long Term
We live in a noisy world. We do noisy jobs during the working day and pursue noisy hobbies in our leisure time. Noise has become a permanent fixture of modern life.
In the last 50 years, our average lifespan has been constantly improving, and it's now thought that by 2050, people will routinely live to be 100. Our hearing mechanism hasn't caught up with such a big change in such a relatively short space of time. Put simply, our ears evolved to cope with a much less noisy, much shorter lifetime of listening.
Little wonder, then, that current estimates suggest 8.5 million people in the UK have some degree of hearing impairment. That's roughly one in eight of the entire population, according to RNID, and a much higher proportion among those over 70.
There are, of course, reasons beyond ageing and noise that contribute to hearing loss: hereditary factors, underlying pathology, head or ear trauma, and exposure to certain ototoxic drugs, to name a few. But the fact remains that advancing years and noise exposure are the two most significant causes of hearing loss. And while nothing can halt the march of time, a great deal can be done to minimise noise exposure.
The difficulty is persuading people to take the risk seriously. Statistics confirming the number of people suffering from noise-induced hearing loss (NIHL) prove that many of us take a dangerously relaxed approach to protecting one of our most valuable senses, especially in the earlier stages of our lives.
We can't stop age-related hearing loss. But we absolutely can take steps to prevent NIHL.
How the Ear Works: A Quick Tour
The human ear has three main sections: the outer ear, the middle ear, and the inner ear, each performing a distinct function.
The Outer Ear
The visible part of your ear is called the pinna. Then there's the ear canal (the meatus) and the eardrum (the tympanic membrane).
The outer ear's job is to collect sound waves (which are actually nothing more than airborne vibrations) in the bowl of the ear (the concha), amplify them at frequencies important for hearing speech (a bit like a built-in ear trumpet, hence its shape), and direct them down the ear canal to the eardrum, which then begins to vibrate.
The Middle Ear
The middle ear is a pressurised chamber inside your skull, directly behind the eardrum. The three smallest bones in the human body live here: the hammer (malleus), the anvil (incus), and the stirrup (stapes).
Collectively known as the ossicles, they connect the outer ear to the inner ear, acting as a kind of crowbar to further increase the energy delivered inward.
The Inner Ear
The inner ear contains the cochlea, a pea-sized organ made up of two fluid-filled galleries. When the stirrup moves the oval window in response to a detected sound, it creates a pressure wave in the upper gallery. This presses down on the lower gallery and, through some remarkable anatomy and thousands of tiny hair cells, generates coded electrical signals that travel up the auditory pathway to the brain, where they are perceived as sound.
It's a fantastically well-designed and efficient system. When working properly, it allows us to:
Detect small changes in volume
Detect small changes in pitch (the average ear's range is 20–20,000 Hz)
Determine where a sound is coming from, both horizontally and vertically
Pick out speech in noise
Detect danger
Hearing Is More Than Mechanics
What's just been described is a simplified account of the mechanics involved in physically receiving a signal. But what a person actually hears depends on rather more than that.
Day-to-day hearing also depends on what the brain does with the signal it receives, a person's general outlook, their auditory memory, how much time they spend actively listening, and their level of interest at any given moment.
People With Normal Hearing
In the vast majority of cases, people with normal hearing thresholds rarely report difficulties in daily life, unless there are extenuating circumstances. Tinnitus can cause issues, as can "selective hearing" (as spouses sometimes label it), distraction, or temporary lapses in concentration.
One interesting exception: people who lead extremely solitary lives. Hearing skills need practice, just like any other. Those of us who regularly engage with people around us practise without effort. But someone who rarely enters a noisy environment may find their ability to discriminate speech in noise gradually diminishes.
People With Hearing Impairment
It's with this group that the subjective factors really start to matter. Hearing care professionals routinely see people who exhibit similar losses on paper, yet experience very different consequences in practice.
Some people withdraw socially as soon as a hearing loss prevents them from easily understanding conversation. Others stay engaged and work to fill in the blanks. No prizes for guessing which group hears subjectively better for longer.
I once met a man in his nineties with a clinically severe hearing loss who communicated as though he had none. He had been a television producer in the early days of TV and had trained himself to listen to three things at once: what was happening on stage, what was coming through his earpiece, and what his assistant was saying beside him. An impressive feat of multitasking that was clearly paying dividends in his later years.
The only person who can hear what you hear is you. Positive, optimistic people tend to expect to hear, while negative, pessimistic people may not. That pattern can easily become self-fulfilling.
How Is Hearing Measured?
Hearing is an entirely subjective experience, measured and recorded using objective means. To make the measurement meaningful, we compare it to a useful average.
0 dB (HL) on an audiogram is that useful average. It is not "no sound". It's the quietest average sound a group of 1,500 twenty-one-year-olds could hear when tested under controlled conditions. Some individuals hear better than this average, hence the −5 and −10 dB (HL) levels on the chart. In other words, 0 dB (HL) represents extremely good hearing, since we're generally in peak physical condition at that age.
How the Test Works
The person being tested wears headphones. A series of tones are played across the frequencies important for hearing speech (typically 250 Hz to 8,000 Hz), and we record the quietest sound they can detect at each frequency. This is done separately for each ear, producing an audiogram.
On the audiogram:
The horizontal axis shows the pitch (frequency) of the sound, lowest on the left (250 Hz), highest on the right (8,000 Hz)
The vertical axis shows the volume needed to just detect the sound, measured in dB (HL)
Air Conduction vs Bone Conduction
Air conduction testing delivers sound through headphones, through the outer ear, into the middle ear, and on to the inner ear. Results are marked as circles (right ear, red line) and crosses (left ear, blue line).
Bone conduction testing places a vibrator on the mastoid bone behind the ear. This bypasses the outer and middle ear entirely, stimulating the inner ear directly. Results are marked as triangles.
Why does this matter? Comparing the two tells the audiologist where any problem lies:
If bone conduction is significantly better than air conduction, it suggests something is reducing the sound before it reaches the inner ear. This is a conductive loss (outer or middle ear problem)
If bone conduction shadows air conduction closely (within 10 dB), there's no conductive component, and any loss is sensorineural (inner ear)
A combination of both is called a mixed loss
If one ear is significantly different from the other, it's described as asymmetrical
If one ear is normal and the other shows measurable loss, it's unilateral (one-sided)
Note for employers: Bone conduction testing isn't typically carried out as part of workplace hearing tests. Hearing tests under the Control of Noise at Work Regulations are for triage purposes, identifying whether there's a potential problem and referring on for diagnostic testing where needed.
Understanding Hearing Loss Categories
Normal Hearing
Experience has shown that people who record thresholds at 20 dB (HL) or better very rarely report hearing difficulties. This has become the accepted definition of "normal" hearing. People in this category tend to say that what they hear is good enough the vast majority of the time.
Impaired Hearing
Category | Threshold Range | What It Means |
Mild loss | 20–40 dB (HL) | Difficulty with quiet speech or background noise |
Moderate loss | 40–60 dB (HL) | Difficulty following normal conversation |
Severe loss | 60–90 dB (HL) | Difficulty hearing most sounds without amplification |
Profound loss | 90+ dB (HL) | Cannot detect most sounds without significant amplification |
Very few people have a hearing pattern that falls neatly into one category. Most hear some sounds better than others, which often serves to deceive, and because people seek help at different stages, they can experience markedly different consequences from what appears to be a similar level of loss.
Putting Sound Into Perspective
To make the audiogram meaningful in everyday terms, here's how common sounds compare:
Sound Level | Typical Example |
0 dB | Threshold of hearing |
30 dB | A bedroom at night |
60 dB | Normal conversation |
90 dB | A handheld drill |
120 dB | A jet aircraft at 100 metres |
140 dB | Threshold of pain |
Even with something this apparently straightforward, there are perceptual differences. A clock ticking in the middle of the night sounds distinctly louder than during the day. Pub and restaurant noise can seem very loud when you first walk in, then settles as you adjust. The reverse is true if your hearing isn't as good.
How Long Can You Safely Be Exposed?
The volume of the noise matters, but so does how long you're exposed to it. In broad terms, 85 dB(A) of constant noise is the highest safe level for eight hours in a 24-hour period. Every 3 dB increase halves the safe exposure time.
Noise Level dB(A) | Maximum Safe Exposure |
85 | 8 hours |
88 | 4 hours |
91 | 2 hours |
94 | 1 hour |
97 | 30 minutes |
100 | 15 minutes |
103 | 7.5 minutes |
106 | 3.75 minutes |
109 | Under 2 minutes |
112 | Under 1 minute |
115 | 28 seconds |
This is why workplace noise assessments are so important, and why the Control of Noise at Work Regulations 2005 set mandatory action levels at 80 dB(A) and 85 dB(A).
What Does This Mean for Your Workplace?
If your workers are exposed to noise at or above 85 dB(A), you're legally required to provide hearing tests (health surveillance) under the Control of Noise at Work Regulations 2005. Even exposure between 80 and 85 dB(A) can trigger requirements if workers are at particular risk.
H4TLT makes workplace hearing testing straightforward. Our self-service system enables compliant annual hearing tests 24 hours a day, 7 days a week. Each test is automatically categorised to HSE standards, with Category 3 and 4 results referred by a competent professional. No mobile van needed, no scheduling headaches, just reliable, cost-effective compliance.
Need to check whether your team needs hearing tests? Try the H4TLT compliance checker to find out in minutes.
Mark Ashmore is a HCPC-registered audiologist with over 30 years' experience in occupational hearing health. Hear 4 The Long Term provides workplace hearing tests, earplug fit testing, and baseline hearing tests for employers across the UK.
Frequently Asked Questions
What do the numbers on a hearing test mean?
A hearing test produces an audiogram, which is a graph showing the quietest sounds you can hear at different pitches. The horizontal axis shows the frequency (pitch) of the sound in Hertz (Hz), running from low-pitched sounds on the left (250 Hz) to high-pitched sounds on the right (8,000 Hz). The vertical axis shows volume in decibels hearing level, or dB (HL), with quiet sounds at the top and louder sounds further down.
If all the results sit above the 20 dB (HL) line, hearing is considered normal. If they fall below that line, there is some degree of hearing loss. The further down the graph the results appear, the greater the loss. For workplace hearing tests, the audiologist will classify results into HSE Categories 1 to 4, so you don't need to interpret the audiogram yourself. Focus on the category and the recommended actions.
What noise level is dangerous at work?
Under the Control of Noise at Work Regulations 2005, there are three key levels employers need to know about.
The lower exposure action value is 80 dB(A), which triggers a requirement for a noise risk assessment and means hearing protection must be made available on request. The upper exposure action value is 85 dB(A), which triggers mandatory hearing protection, hearing protection zones, and compulsory hearing tests for exposed workers.
The exposure limit value is 87 dB(A), which must never be exceeded even when hearing protection is taken into account.
The duration of exposure matters as much as the volume. At 85 dB(A), the maximum safe exposure is eight hours. Every 3 dB increase halves that time, so at 91 dB(A) the limit drops to two hours, and at 100 dB(A) it is just 15 minutes.
What is the difference between noise-induced hearing loss and age-related hearing loss?
Age-related hearing loss (presbycusis) is a gradual, natural decline in hearing that affects most people as they get older. It tends to affect higher frequencies first and progresses slowly over decades. There is no way to prevent it.
Noise-induced hearing loss (NIHL) is caused by exposure to excessive noise, either over a long period or from a single very loud event. It also tends to affect higher frequencies and often shows a characteristic "notch" at 3,000 to 6,000 Hz on an audiogram.
The critical difference is that NIHL is entirely preventable through proper noise control, hearing protection, and regular hearing tests. This is why the Control of Noise at Work Regulations 2005 exist, and why workplace hearing surveillance programmes are a legal requirement for workers exposed above 85 dB(A).
How is a workplace hearing test different from a clinical hearing test?
A workplace hearing test (health surveillance audiometry) is a screening tool. Its purpose is triage, not diagnosis. It measures air conduction only, meaning sound is delivered through headphones and the test records the quietest level you can hear at each frequency.
Results are classified into HSE Categories 1 to 4, which tell the employer whether the worker's hearing is acceptable, showing early signs of change, or needs referral to a specialist.
A clinical hearing test goes further. It typically includes bone conduction testing, where a vibrator placed behind the ear bypasses the outer and middle ear to test the inner ear directly. Comparing air and bone conduction results allows the audiologist to determine the type of hearing loss (conductive, sensorineural, or mixed) and its likely cause.
Clinical tests may also include speech discrimination testing and uncomfortable loudness level testing. These diagnostic tests are what happens after a workplace screening identifies a potential problem.
What are the early signs of hearing loss at work?
The most common early signs include difficulty following conversations in noisy environments like canteens or busy workshops, frequently asking people to repeat themselves, turning up the volume on radios or phones higher than colleagues do, and struggling to hear in meetings or group discussions. Workers may also report a ringing or buzzing in their ears (tinnitus), which is often an early indicator of noise damage.
From an employer's perspective, the signs to watch for include workers who seem to ignore spoken instructions (particularly in noisy areas), complaints from colleagues about someone not responding, and workers who remove hearing protection because they say they "can't hear anything" with it in.
Regular hearing tests are the only reliable way to detect hearing loss early, because most people don't notice gradual changes in their own hearing until the loss is already significant.
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