Vibrations transmitted through an elastic medium (air, water or solids), with frequencies in the approximate range of 20 to 20,000 hertz, capable of being detected by ears is known as sound.
Noise is a sound that is undesired, unexpected, unpleasant or loud. Undesired in that it interferes with sleep, rest, recreation, work or communication the word noise comes from the Latin word nausea meaning sea sickness.
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“Noise pollution is defined as environmental noise or an unwanted sound that is annoying, distracting, or physically harmful. Harms include hearing loss, stress, sleeplessness etc. Noise pollution is also known as sound pollution.””
There are about 25000 hair cells in our ear which create wave in our ear, corresponding to sound in the environment, as a response to different levels of frequencies. With increasing intensity/pitch/loudness of sound the cells get destroyed decreasing our ability to hear the high frequency sound.
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Decibel (dB) is used as a measure of sound intensity level or sound pressure level. It is named after Alexander Graham Bell, the inventor of the telephone.
Sources of Noise:
Source is the equipment or process directly responsible for sound generation. The major sources of noise are summarized below:
(i) Transportation sources:
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Examples Railways, Road traffic and Air traffic
(ii) Industrial sources:
Examples Noise is generated in mostly all of the industrial activities such as power generation, processing, product fabrication and product assembly.
(iii) Public address system sources:
Examples Use of loud speaker at any occasion like marriage function, festival, etc
(iv) Agricultural machine sources:
Examples Use of tractors, tubewells, farm machines for agriculture
(v) Defence equipment sources
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Examples Shooting practices, wars, bomb explosion, etc
(vi) Household sources:
Examples Mixer-grinder, lawn mowers, food blenders, vacuum cleaners, etc.
(vii) Other sources:
Examples Rock concerts, barking dogs, construction equipments, etc
Effects of Noise Pollution
Noise affects human health in following ways:
(i) Physical effects:
Examples Damage to ear drum, temporary impairment of hearing, permanent deafness.
(ii) Physiological effects:
Examples Muscular strain, headache, eye strain, decreased color perception, nervous break down, pain in heart, etc.
(iii) Psychological effects:
Examples Emotional disturbance depression, fatigue, frustration, irritation, reduced efficiency, etc.
Control of Noise Pollution:
Noise pollution can be controlled by reducing noise at the source, interrupting the path of noise and/or protecting the receiver.
(i) Noise control at the source:
It is most effective to eliminate noise at the source.
Examples
(a) Reduction of noise generated by mechanical vibration of a machine by damping or isolation of the vibration by applying damping material (rubber) to the vibrating components.
(b) Reduction of impact force by optimizing the impact-distance and covering either or both impact surfaces by rubber.
(c) Modification of manufacturing design like enclosing the engine parts within proper noise insulating material.
(ii) Noise control at path:
When source cannot be made quiet, noise can be controlled by modifying the path.
Examples:
(a) Attenuation of noise by moving source of noise away from sensitive area.
(b) Suppression of noise from automobiles using silencers.
(c) Reduction of noise around residential areas by planting trees in the form of green belt.
(d) Reduction of transmission of noise using acoustic screens and barriers.
(e) Enclosing noisy machines in isolated buildings.
(iii) Noise control at receiver:
If source and/or path control do not work, control at the receiver should be explored.
(a) Use of hearing protection devices (HPD) like ear plugs, ear muffs etc. They reduce the level of noise (by 10 dB to 55 dB) entering the outer and middle ears before it reaches the inner ear.
(b) Enclose receiver.
(c) Relocate receiver.