Noise may originate from natural sources as well as through anthropogenic activities. The natural sources are cyclone, thunder, roaring of sea, volcanic eruption, etc.
The anthropogenic sources are heavy machineries used in the industry, mechanized automobiles, trains, aero planes, washing machine, television, etc. The anthropogenic noise can be classified into
(i) Transport noise (ii) Occupational noise (iii) Neighbourhood noise
(i) Transport Noise:
For simplification, transport noise is subdivided into three categories:
(a) Road traffic noise (b) Rail traffic noise (c) Aircraft noise
(a) Road Traffic Noise:
The main causes of road traffic noise are the number of road vehicles and their high traffic speed. Heavy vehicles with faster speed create the maximum noise on the road. For example, heavy diesel engine trucks are the nosiest vehicles.
All around the world, the traffic peak hour is from 10:00 a.m. in the morning to 6:00 p.m. evening. The traffic noise level is measured on the Z-10 (18 hours) index. The limit of noise level prescribed in India is 80 dBA, but is never followed.
(b) Rail Traffic Noise:
It is not that serious like road traffic noise and aircraft noise. The noise is of lower frequency compared to road traffic noise. Introduction of diesel or electrical engines in place of steam engine, welded tracks and improve coaches has contributed a lot in reducing noise.
Moreover, most railway tracks run through rural areas which are wider places surrounded by plants and trees. However, buildings located near railway tracks are exposed to noise menace. The rail traffic noise is measured on 1 scale.
(c) Aircraft Noise:
Aircraft noise is not created continuously but is intermittent. The noise is produced during takeoff, landing and flight. The faster and larger the aircraft, the more is the noise and thus, jet engines create the most noise. Although lesser in number, the aircrafts like fighter aircrafts which fly supersonically, become the nosiest source.
(ii) Occupational Noise:
This is mainly produced by industrial machines and processes like blasting operations, shipbuilding, factories and mills producing different kinds of products. Occupational noises are also due to machines used for domestic purposes such as television, washing machines, vacuum cleaners, etc.
In industries, factories or mills, the workers are exposed for five days with 8 hours per day. In their houses, they are getting exposed for a longer duration, although frequency is lower compared to industry and factories. Millions and millions of people working in the industries are the main victims. The high degree of noise causes lowering of hearing capacity to a great extent.
(iii) Neighbourhood Noise:
There are a variety of sources of noise that disturb and annoy people by interfering with their comfort. The sources are loud TV, stereo, radio sets, barking of dogs, garaging the automobiles, starting of the two wheelers used by people, without considering the harmful effects which they might have on the nearby neighbours.
The use of machines for building construction and building demolition are also sources of serious nuisance. Use of loud speakers at public functions, in disco music and dance in late evenings also causes noise nuisance to the nearby residents.