Perceiving noise

Noise is defined by the World Health Organisation (WHO) as “unwanted sound”.

The intensity of perceived noise depends on sound pressure, which is measured using a logarithmic scale and the conventional unit of measurement known as the decibel.

The diagram shows some examples of noise sources and related levels of sound pressure.

According to current rules, noise pollution from road traffic is measured in “weighted equivalent noise level A” espressed as [dB(A)] i.e. a parameter that takes an average over time of the individual noise events caused by vehicles passing according to the sensivitity of the human ear. (weighting A).