Noise Control Techniques:
Noise Control Techniques: Before considering method of noise control it is important 0 remember that the noise at any point may be due to more than one source and that additionally it may be aggravated by noise reflected from walls (reverberant noise) as well as the noise radiated directly from the source. With any noise problems there are three distinct elements -Source, Path and Receiver.
Having identified the nature and magnitude of any noise problem the essential elements of a noise control program are provide. Where a problem is evident there are three orders of priority for a solution’s
- Engineers solves this problem by changing to low noise equipment, altering the process or changing operating procedures.
- Apply conventional method of noise control such as enclosures of silencers.
- Where neither ‘of the above approaches can be used, the last report of providing personal protection should be considered
Although the control of noise at source is the most obvious solution the feasibility of this method is often limited by machine design, process or operating methods, while immediate benefits can be obtain this method should be regarded as a Long Term Solution.
Noise Control Techniques by Control of noise at source
Design of equipment and process play vital role in controlling noise at source.
Selection of the Process
Select welding instead of riveting.
- Hydraulic riveting instead of Pneumatic riveting.
- Grinding or Flame Gauging instead of Chipping.
- Mechanical Ejector instead of Air Ejectors.
- Hot working of metal instead of cold working.
Selection of Equipment
- Machines With rubber and plastic parts
- Nylon gears instead of steel or cast iron gears.
- Helical gears instead of spur gears.
- Lining of chutes
- Paving Brakes
- Use of anti-vibration mounts
Effective noise reduction practices:-
A number of practical techniques can be used as part of normal day to day operational and maintenance procedures that will achieve significant reductions in the noise emitted, will cost nothing or very little tom implement and can additionally give worthwhile savings in energy. Some of these techniques are listed below.
- Tighten loose guards and panels
- Use anti- Vibration mounts and flexible couplings
- Planned maintenance with program for regular lubrication for both oil and grease.
- Eliminate unnecessary compressed air and steam leaks, silence air exhausts.
- Keep machinery properly adjusted to manufacturer’s instruction,
- Use damped or rubber lined containers for catching components
- Switch off plant not-in sue especially fans.
- Use rubber or plastic bushed in linkages, use plastic gears.
- Re-site equipment and design in noise control
- Specify noise emission levels in order i.e. 85 dBA at 1 meter.
- Check condition and performance of all installed noise control equipment
Noise Control Techniques by Noise cancelling
Recent experiments to cancel the effects of noise electronically by emitting a signal that effectively flattens the noise wave shape have achieved some success in low frequency operation and situation where the receiver position and the source emission are well defined:
Orientation and Location
Control may be achieved by moving the source away from the raise sensitive area. In other case where the machine does not radiate equally in’ all directions, turning it around can achieve significant reduction.
Enclosures which give an attenuation of between 10 and, 30 dBA are the most satisfactory Solution since; they will control both the direct field and the reverberant field noise components. The sound reduction, attenuation or insertion loss defined as the difference sound pressure level before and after the enclosure. A typical enclosure constructed of an outer heavy wall with an inner lining of an acoustically absorbent material like glass wool or mineral wool perforated thermo Cole.
Noise Control Techniques by Silencers
Silencers used to suppress noise generated when air, gas or steam flow in pipes or ducts or exhausted to atmosphere. They fall into two forms:
- Absorptive, where sound absorbed by an acoustical absorbent materials.
- Reactive, where noise reflected by changes in geometrically shape
- Performance depends on Physical dimension.
- Sound reduction or insertion loss increases with length.
- Low frequency performance increases with thicker splitters and reduced air gap.
Pipes lagged with mineral wool with an outer steel aluminum or lead leaded vinyl layer can achieve attenuation between 10 and 21 dBA.
Where large panels radiating noise a significant reduction can achieved by fitting proprietary damping pads, fitting stiffening ribs or using a double skin construction.
Acoustic screens are effective in reducing the direct field component noise transmission y up to 15 dBA. However, they are of maximum’ benefit ‘at high frequencies, but of little effect at low frequencies and their effectiveness reduces with distance from the screen.