Noise can be defined as unwanted sound. Whether a sound is pleasant or a noise depends upon loudness, duration, rhythm and the mood of the person. The most immediate and acute effect of noise pollution is impairment of hearing, anxiety and stress and in extreme cases fright. Physiological manifestations; increase in the rate of heart beat, constriction of blood vessels and dilation of pupil of the eye.
Loudness is measured in terms of decibels (dB). Just audible sound is about 10 dB, a whisper is 20 dB, and a normal conversation is 35 – 60 dB. Sound beyond 80 dB can be safely regarded as pollution as it harms the hearing system. World Health Organization has fixed 45 dB as the safe noise level for a city.
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