The term noise may be defined as unwanted sound. A given sound may be music to one person’s ears but noise to another’s, pleasant when soft but noisy when loud, acceptable for a short time but non-acceptable when prolonged, intriguing when rhythmic but noisy when randomly repeated, reasonable when you make it but noisy when someone else makes it.
Of all the attributes that distinguish wanted and unwanted sound, the one considered most significant is loudness. There is ample evidence that prolonged exposure to loud sound is harmful in various ways – the louder a sound is, the more likely it is to be considered noise.
Awareness of these problems has increased in recent years and any comprehensive discussion of the environmental problems must now include a study of noise, along with the more traditional problems such as air pollution, water pollution and solid waste disposal.
Image Source : environment-today.org
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Unfortunately, noise pollution has not been given enough importance in this country. Besides, there is no statutory standard for this purpose in India. The instruments required for measurement of sound level have not yet been fully developed in this country and, hence, are not easily available for measurement of sound level.
However, there is an urgent necessity to scientifically monitor sound levels in large cities, in the engineering industry and in large as well as medium chemical, metallurgical and other industries.
Excessive noise could adversely affect productivity which is already low in India in comparison with advanced countries. The elimination of noise should also help prevent accidents. It is also known that noise has a delayed impact resulting in loss of hearing.
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Therefore, it is essential to take suitable precautions, especially when children or young persons are involved. Suitable introductory material along with pollution abatement techniques.
Sound is a form of energy and requires a medium which may be a gas, liquid or solid for its propagation. Any vibrating surface such as a loudspeaker diaphragm which moves to and fro, generates sound.
As the diaphragm moves forward, it compresses the portion of the gas nearest it. Because of the forces developed by this compression, portions of the gas farther away are progressively set in motion as the inertia of the air molecules is overcome.
When the diaphragm reverses its direction of motion, it produces a rarefaction of the gas near it, and a movement of the air particles farther away occurs progressively in the opposite direction. Every small volume containing molecules, wherever located, oscillating forward and backward, under the influence of the diaphragm, will cause molecules further away to oscillate at the same frequency.
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The inertia of the particles and the poor elasticity of the gas cause the disturbance (the pressure-variation the sound energy) to travel at the relatively slow speed of around 340 ms. The extent of the disturbance depends upon the initial intensity, the dissipative losses in the gas, the presence of wind, turbulence, temperature gradients and on the boundary surfaces.