Our Interpretation of Sound.

What is the difference between sound and noise?
In practical terms, the difference between sound and noise is difficult to define objectively. In general, any unwanted sound is considered noise. Generally, if the form of a sound wave consists of regular vibrations it is usually described as being pleasant, whereas random waveforms are more likely to be classed as noise. In reality whether or not a sound constitutes noise depends on the circumstances in which it is made: loud parties, late at night, might be enjoyed by those who are at the party but the next door neighbours, trying to sleep, may well complain about it being too noisy! Thus noise can be considered a form of air pollution, but sound is not.

How is noise measured?
Noise is measured in decibels, written dB for short, which is a logarithmic scale. The logarithmic scale differs from the linear scales that are used to measure length (mm, cm, m, km) and is suited to the measurement of sound as it roughly corresponds to our hearing sensitivity. That is to say, as the sound becomes louder so our hearing sensitivity decreases. The speed of sound is 340 metres per second (m/s) in air, 1500m/s in water and 5000m/s in steel. The speed of light is 300,000,000m/s, which is why you sometimes see lightning several seconds before hearing the thunder. The two are produced together but travel at different speeds.
• An increase of 1 dB is just about noticeable
• An increase of 10dB sounds twice as loud
• Sound as loud as 120 dB can cause pain
• Sound as loud as 200 dB can bore holes in solid material and could even kill you!

The energy of sound the human ear can hear without pain is about 10 million times greater than the faintest detectable sound. Using the logarithmic scale means that we cannot simply add the sounds of 2 noise sources together to produce a total e.g. whilst one lorry may be measured as producing 70 dB, two identical lorries passing simultaneously will not give 140 dB but 73 dB. Whilst the noise of the first lorry is noticeable, the additional noise of the second lorry is perceived to a lesser degree.

Damage limitation and methods of protecting our hearing.
Noise damage can occur without you realising it. It is an invisible, cumulative process and the damage is permanent. It's not just hearing loss; tinnitus (a persistent ringing or rushing in your ears) or becoming unusually sensitive to sound are also distracting and uncomfortable side effects of hearing damage.
• If you cannot talk to people two metres away without shouting because of background noise, the noise is at a dangerous level.
• If after listening to a loud noise you cannot hear properly for a few hours or you hear ringing in your ears, this is a sign that the sound was loud enough to damage your hearing.

At night-clubs and rock/pop concerts
• Take regular breaks from the dance floor and make use of the chill-out rooms.
• Wear ear plugs if you go to clubs or live gigs regularly; many DJs and musicians use them to protect their hearing.
• Make sure you stand away from loudspeakers.
• Watch out for signs of hearing exhaustion e.g. ringing in the ears or dullness of hearing.

When using personal stereos.
• Turn the volume down - don't turn the volume up to drown out background.
• Reduce the length of time you listen to your personal stereos.

Finally if you are worried about your hearing consult your doctor!