Noise is often defined as ‘sound which is undesired by the recipient’. A sound which one person finds enjoyable, such as some music perhaps, could be very annoying to another person who doesn’t want to hear it. Since it is quite probable that whatever the noise, there will be someone who doesn’t like it, there is a common presumption that all sound is bad. This presumption is even the basis of some legislation, which often seeks to limit sound levels on the basis that any sound could be annoying to someone.
However, this presumption is by no means always true. Individual sensitivity to noise varies greatly and some people are not bothered by noise that would be intolerable to others. Moreover, there are many situations where noise is appropriate: for example a football match conducted in silence would be unnatural and hardly enjoyable for fans.
In English law, it is illegal to create noise which amounts to a nuisance, but in Common Law, the test is whether an ordinary person, taking account of the circumstances, would find the noise to interfere with the ‘enjoyment’ of their land to a material degree. Statute Law has changed the situation in recent years, and objective noise tests are becoming more important.
It is relatively easy to devise noise indexes that can measure sound level, but because noise perception is subjective (ie it depends on the listener), acousticians have not been able to find a perfect unit or index for measuring noise annoyance or disturbance.
This means that acousticians use a variety of noise indexes that describe sound levels in a variety of ways. Using these as a guide to the impact of noise on people requires careful interpretation by skilled practitioners.
However, increasing regulation, both national and European, is changing the situation, so that assessments are now more likely to depend on assessing sound levels in accordance with a defined procedure and for the result to be compared with objective guidelines.
Very often it is necessary to show in advance that a scheme will have an acceptable noise impact. This requires noise levels to be predicted or calculated before the scheme is approved. NoiseMap software has been developed and used in this process for over 40 years.