Can noise damage your hearing?

Whether sound waves are loud or quiet depends on their frequency, and also on something called the sound pressure level.

The frequency determines the pitch of a sound. It tells us how often the sound wave vibrates per second and is measured in hertz (Hz): 60 hertz means 60 vibrations per second. The higher the frequency, the higher the pitch.

Our hearing isn't designed to pick up all sound waves. For example, we can't hear ultrasound because the frequency of ultrasound waves is too high. Nor can we hear sound waves with a very low frequency (known as infrasound). But we can hear sound wave frequencies between the two. Our hearing is particularly sensitive to certain frequencies in that range, including those frequencies produced by the human voice.

In simple terms, the sound pressure level tells us how strong sound waves are. The sound pressure level is often simply called the volume. It is measured in decibels (dB).

If the sound pressure level is too low even though the frequency of the sound wave is in our hearing range, we still can't hear the sound. We can only hear it if the sound pressure level is above a certain amount of decibels. This is called the hearing threshold.

The higher the sound pressure level rises, the louder we hear the sound. But things become unpleasant above a certain volume. Our threshold of discomfort is crossed. Many people then instinctively cover their ears.

If the sound pressure level is even higher, the volume becomes painful. At that point the threshold of pain has been crossed. Depending on the frequency, this threshold lies at around 120 to 140 decibels. Noises in that range and above can lead to immediate hearing damage. This type of injury is also known as acute acoustic trauma. It can be caused by things like the bang of an explosion. The very high volume damages the sensitive sensory cells in the inner ear. Very high sound pressure (e.g. from an explosion or a strike to the ear) can also injure parts of the middle ear or the eardrum.

People with acute acoustic trauma experience short, stabbing ear pain. Their hearing is then impaired for a while after, and sometimes even permanently. People often develop tinnitus at the same time, which then only disappears slowly. If an eardrum bursts or other parts of the ear are injured, blood may come out of the ear.

Long-term hearing problems aren't only caused by acute acoustic trauma. They can also be caused by frequent exposure to noise below the pain threshold. It is not possible to generally say what volume that begins at. Sensitivity to noise can differ from person to person. The risk of noise-induced hearing loss is said to be greater above 80 to 85 decibels. But it depends on how long you are exposed to the noise per day or per week. It is also worse if the noise keeps suddenly getting louder rather than staying at a constant volume.

Some people may be at risk of damaging their hearing at their workplace – for example, if they work with loud machines and don't use proper ear protection. But they may damage their hearing in their free time as well – for instance, if they do DIY with loud machines, or if they often listen to loud music at concerts, in clubs, or through headphones. Experts assume that the risk of hearing loss is increased if you listen to loud music for longer than one hour every day for years. It is considered to be “loud” if you listen to it at more than half the device's maximum volume.

Short-term hearing problems can occur after each exposure. Then your hearing is slightly worse for a few minutes or maybe even a few hours, as if you have cotton wool in your ears. A ringing or other sounds might be heard at the same time. But you may not notice anything at first, even though sensory cells have been damaged. Permanent hearing loss can develop over several years.

This chronic noise-induced hearing loss is similar to age-related hearing loss in some ways:

• Both ears are affected.
• The inner ear is damaged (known as sensorineural hearing loss).
• The hearing problems are initially limited to sounds in the upper frequency range. That makes it harder to hear birdsong, the telephone or the doorbell, for example. As things progress, it becomes more difficult to follow conversations, especially if there are other sounds in the background (e.g. other voices, traffic or music).

Noise-induced hearing loss can ultimately lead to total loss of hearing (deafness).