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1. Loud but clear

Protecting your ears
The inner ear is where sounds are turned into electrical signals that go to the brain. It is the tiny hairs on the cochlea that pick up the sound vibrations. These hairs can easily get damaged if they are made to vibrate too vigorously – especially if this is continuous. Any damage to the inner ear cannot be reversed.
Photo of cochlea
Picture 7. A microscopic photograph of the hairs inside the cochlea. There are some damaged hairs in the bottom left. Photo courtesy of The Hospital for Sick Children, Toronto.
What sound can cause damage?
A passing train is loud (90 decibels). Although this would not cause immediate damage, continuous exposure to this level can cause hearing loss. After 40 years of being exposed to this level for a working day of eight hours, 60% of people would lose their hearing.
Noise in factories
Some factories can be this noisy, i.e. with a sound level of 90 dB. To get an idea of how loud it is, it would make you shout at someone a couple of metres away in order to be heard. Clearly there is a potential hazard for anyone working in this sort of environment for any length of time. Corus take steps to reduce noise in their factories and provide ear defenders for anyone who works in a noisy environment. The recommended threshold is 82 dB.
Reducing sound levels
Sound travels well through solids - better than it does through the air. However, when it meets a barrier, like a solid wall, some of the sound is reflected and some gets through. Although the air and the wall can carry the sound well, it is the boundary between them that reduces the level.

Therefore, if we have more than one boundary, the sound will be reduced more. This is why double glazing is effective at keeping noise out. It is also why foam and cardboard are good at reducing noise level. Although they are solids, they don't have a rigid structure that carries the sound from one side to the other. They have lots of tiny air pockets - so there are lots of little boundaries that reduce the sound level.

Ear defenders
Photo of earplugs
Picture 8. Ear defenders. They can be squashed to fit in the ear. For extra protection, use ear muffs as well.
Ear defenders are simple but effective. Usually, they are small plugs of expanding polyurthane or PVC. You squash them between your fingers and then fit them into your ear. They expand in the ear canal, making a snug fit.

The material absorbs the sound effectively. Typically, these ear defenders can reduce the sound level by 30 dB. The level reaching the ear drum can then be well within safe limits, even if the surrounding noise is up to 90 dB.

In extremely noisy environments, you should wear ear muffs as well as the plugs. These can reduce the noise level by a further 10 dB. Their soft foam padding absorbs the sound and, importantly, makes a snug fit against the side of the head - any air gaps will let the sound through.

Question 1-4.

a) Look at the paragraph below. There are three blanks and three choices. Fill in each blank with the correct word (make sure you spell them correctly) and make a choice from the pull down lists.

The is the part of the ear that turns sounds into electrical signals. Tiny in there vibrate when there is a sound. Once they are damaged they be repaired and a person will suffer some form of . People exposed to a level of more than about 80 dB should wear .

Summary                   Close
  • Continual exposure to sounds more than 80 dB can cause hearing loss
  • Factory workers should wear ear defenders