You can tell by the number of people you see with cables hanging from their ears that listening to personal music players is very popular. Not only do you see the cables, but sometimes you can hear the music too. Listening to music this way is known as leisure noise and it’s not a great deal different from noise at work. But when people are at work there are regulations to prevent them from suffering long term hearing loss. For people listening to personal music players there are no such regulations and listening at high volume levels for long periods of time may put them at risk of developing noise induced hearing loss.
To understand how it’s possible to develop noise induced hearing loss we need to look at how we hear. The process of hearing starts in the outer ear. The Pinna on the side of your head, which we normally call the ear, helps collect the sound and feed it into the ear canal where it vibrates the eardrum. On the other side of the eardrum in the middle ear are three small bones that transfer the vibrations of the eardrum to the Cochlea. The Cochlea is part of the inner ear and has special hair cells that pick up these vibrations and change them into electrical signals for the brain.
The amount of sound energy picked up by your ear is related to the intensity of the sound and how long you listen to it. When your ear is exposed to excessive sound energy, some of the hair cells in the Cochlea are damaged. These damaged hair cells do not grow back. If your ear is repeatedly exposed to excessive sound energy, the damage builds up over time. This is called noise induced hearing loss.
How do you know if the sound energy you hear is too much? Well sound intensity levels are measured in decibels, which is a ratio based on a logarithmic scale. When you double the sound intensity the measurement goes up by 3 decibels. If you increase it 100 times it goes up by 20 decibels. In 2006 the European Union Noise at Work Regulations set an exposure limit of 80 decibels for 8 hours a day, five days a week or 40 hours per week before action should be taken to protect the hearing of workers. To give an idea of where this limit fits into our everyday lives, a normal conversation is about 60 decibels, an aircraft taking off nearby is about 120 decibels and pain happens at around 140 decibels.
The limit of 80 decibels is not a fixed limit, but can be applied using the principle of equal energy. This means that if you increase the sound intensity you must reduce the exposure time to keep the risks the same. For example, if you double the intensity to 83 decibels (remember it’s a logarithmic scale) you must halve the exposure time to 20 hours per week. If you increase the sound level to 89 decibels you must reduce the exposure time to five hours per week. These limits have implications for people using personal music players. If you use your personal music player for one hour a day, seven days a week at a sound level of 89 decibels, you will be breaking those regulations by two hours per week and at risk of noise induced hearing loss.
A European study in 2008 looked at a number of personal music players and found that they had maximum sound levels that ranged from 80 decibels to 115 decibels using standard earphones. But if the ear-bud type of earphones that fit into the ear canal were used maximum levels of 120 decibels were possible. Recent European Union legislation stated that a personal music player used with earphones must only be able to output a sound level of 100 decibels when on maximum volume.
Setting this limit does not necessarily help though. If some people listen to personal music players for long periods of time at volume levels above 80 decibels the evidence suggests they may suffer noise induced hearing loss in the long term. So the advice is to keep the volume to around 60% and give your ears a rest with regular quiet times.