It is, however, impossible to have a total elimination of annoying sounds. Noise pollution can be reduced or noise control can be done mainly by planning and forethought.
The passive barriers, isolators, distances and absorbers which give rise to an acceptable noise level have been usually permanent features of our environment and as such they will not be easy to adapt or vary, and so must be adequate when installed, and permit for possible increases in future noise levels.
Silence can only be achieved in two ways; either the noise source should be switched off, thus depriving someone of a facility, or else the noise suffers must move away until he can no longer be able to hear the sound. The concept of an ‘acceptable’ level’ often involves setting of standards by an arbitrating body like government and Court of law. Decisions must be made involving a tradeoff between utility and noise.
Now we can say noise control can be achieved by:
(a) Noise control at the source of the noise.
(b) Noise control along the path that the noise takes and
(c) At the point of reception.
Over all these aspects is the necessity to plan well and to educate people and organizations to consider how avoidable noise can be eliminated and how unavoidable noise can be reduced.
Noise Control at Source
There are at least primary areas in which control of noise generated by a source may be initiated: proper design, proper equipment operation and equipment maintenance.
In a very general way source of the things that may result from good noise design and operation are:
1. Using shock absorbing techniques for absorbing impact energy (for example, the use of non- metallic gears to reduce the noise generated by the metal-to-metal impact associated with metallic gears the use of flexible mounts to support wood planer knives to reduce the noise generated by the impact of the knives on the board).
2. Proper lubrication and better maintenance of machines.
3. Installing noisy machines in soundproof chambers.
4. Reducing the noise produced from a machine by vibration damping i.e., making a layer of damping material, rubber, neoprene, cork or plastic) beneath the machine.
5. Using silencers to control noise from automobiles ducts; exhausts etc. and convey systems with ends opening into the atmosphere.
Noise Control at Receiver’s End
Noise has been received by people and more exceptionally by delicate instrumentation and it is often necessary to control the level of the noise received. This is normally achieved by treating the room or area within which the receiver is situated and using protective devices.
Normally, the permissible noise levels have been set for the receiver, and engineering techniques must be used on the source and/or paths in order to limit the exposure of the receiver.
For people working in noisy installations, ear-protection aids like earplugs, earmuffs, noise helmets, headphones etc. must be provided to reduce occupational exposure.
It is possible to control both the exposure time and the level for workers by arranging their work pattern in way, which would limit the amount of time that they spend in certain noise level environments.
Sound Insulation at Construction Stages
(a) Sound travels through the cracks that get left between the door and the wall. For reducing noise, this space (jump frame gap) should be packed with sound absorbing material.
(b) Sound insulation can be done by constructing windows with double or triple panes of glass and filling the gaps with sound absorbing materials.
(c) Acoustical tiles, hair felt, perforated plywood etc. can be fixed on walls, ceilings, floors etc., to reduce noise.
Strict legislative measures need to be enforced to curb the menace of noise pollution. Some of these measures could be:
(a) Minimum use of loud speakers and amplifiers especially near silence zones.
(b) Banning pressure horns in automobiles.
(c) Framing a separate Noise Pollution Act.
Permissible Noise Limits
Under Central Motor Vehicle Rules, 1989, the following limits were imposed on 26lh March 1993.
Noise Pollution-The Situation Today
In urban localities all over the world, noise pollution has been recognised as a major factor affecting public health and well being. It is an ever growing nuisance. Man-made sources are mainly responsible for increasing the ambient noise level in urban localities.
Automobiles, industrial units, low flying aircraft and loud speakers have been recognised as a major source of noise affecting a large number of peoples.
A survey in Delhi, Mumbai and Kolkata conducted in 1988 revealed day time noise levels ranging between. 60 dB to 90 dB in residential localities many times during the day this level exceeded 100 dB.