Noise
Noise which can cause damage to our ears comes in many forms. Noise emissions from industrial machines, road-working equipment, drills, lawn mowers, aeroplanes, firearms and loud music, all have potential to cause damage to hair cells within the hearing organ (cochlea), leading to a hearing loss as described below.
Mechanism of how loud noise damages our hearing
The diagram on the previous page demonstrates the pathway of how sound is heard. Sound waves travel down the ear canal (1) and vibrate the ear drum (2). This vibration causes three tiny bones in the middle ear (3) to move against the cochlea (4). The cochlea consists of three fluid filled compartments which bathe the structures that allow us to hear (5) including the outer hair cells (6). On top of the outer hair cells are tiny hairs called stereocilia (7). When sound waves travel along the basilar membrane inside the cochlea they move the outer hair cells and its stereocilia. Stereocilia bend as they push up against the tectorial membrane and send messages through the hearing nerve (8) to the brain. When the sound is too loud, the stereocilia are forced up against the tectorial membrane causing the tiny hairs to break, resulting in loss of hearing. This hearing loss may be temporary or permanent.
Noise and the damage to our ears
Following exposure to a loud noise, stereocilia is damaged or broken and the outer hair cells swell. This causes a hearing loss at the mechanism which allows us to hear and the hearing loss may be temporary or permanent.
A Temporary Threshold Shift (TTS) causes reduced hearing ability and tinnitus (head/ear noises). Although the effects usually last less than an hour, it is possible for symptoms to last many hours or even days as the cochlea regenerates and reduces the swelling of the hair cells. If the damage in TTS is extensive, the hearing loss can become permanent.
A Permanent Threshold Shift (PTS) occurs when there is incomplete recovery after TTS. The swollen hair cells rupture beyond repair as a result of prolonged noise exposure.
Noise intensity and duration
Noise can be steady, fluctuating, intermittent or impulsive, but all can be equally damaging. With increasing noise volume (noise intensity) and the longer that a person is exposed to noise (noise duration), the greater the risk of TTS or PTS. For example, a moderately loud sound may be tolerated for eight hours before causing damage; however a very loud noise may cause damage in less than one hour.
You can reduce the risk of damage to the hearing by reducing the volume and/or the amount of time listening to loud sounds e.g. move further away from the noise source, wear plugs to dampen the sounds or take listening breaks in a quiet area.
Hearing protection
Correct use of hearing protection when exposed to loud noise will decrease the chance of permanent hearing loss. For further information of hearing protection, consult your audiologist.
Personal listening device use
Personal listening devices, such as MP3 players, laptops, tablets and smartphones, used with headphones/ear buds can get surprisingly loud. Listening for more than five minutes at full volume could be putting your long-term hearing at risk.
However extended listening at 10 to 50 per cent of full volume has shown to cause no hearing problems1. People also tend to increase the volume when in places with background noise, such as crowds of people, or on public transport.
In these situations, earphones which actively or passively reduce background noise can help the user listen to music at a lower, safer volume. Many devices can also have volume limiters set, which can be locked; a useful feature for parents.
[1] Study recommends safe listening levels for iPod use, CBC News (2006). http://www.cbc.ca/news/health/story/2006/10/19/music-earphones.html
