Noise enclosure

Type outdoor type pre-fabricated Steel Sound Attenuating Enclosure Noise Level 80 dB(A) at 1 m... 

Uses. Sound-absorbing materials are frequendy used to reduce reverberation, or the persistence of sound in a space after generation of the sound ceases to reduce focused reflections from concave surfaces to prevent echoes, or delayed sound reflections from distant surfaces and to prevent the buildup of sound by multiple reflections within rooms and other enclosures. Sound-absorbing materials also are used to reduce the transmission of noise from one location to another by multiple reflections from sound-reflecting surfaces. 

Other considerations are (I) proper ventilation and discharge enclosures, (2) provision for relief of internal explosion, (3) vibration isolation (shock mounts), (4) remote operation of charge and discharge, (5) noise during operation. 

The philosophy of any EMI shield is to encourage eddy currents to flow within the surfaces, thus dissipating the noise energy. Also, the assembled enclosure should act as a gaussian enclosure where there is good electrical conduction totally around the enclosure. So removable hatches and enclosure members need very good electrical connections around their peripheries. RF gasketing is sometimes used in particularly troublesome cases. 

Leads that enter or exit the enclosure ideally should have their associated EMI filters at the point of entry or exit from the enclosure. Any unfiltered leadlengths that run within the enclosure will inductively pick-up noise within the case and allow it to exit the case, thus making any EMI filtering less effective. Likewise, any unfiltered leads within the case will radiate any transients from outside the case into the case, which may affect the static discharge behavior of the contained circuits to external static events. 

As a side benefit, on electric arc furnaces the enclosure offers a great potential for noise control. 

In addition, they are usually constructed without isolation valves on the fuel supply lines. As a result the final connection in the pipework cannot be leak-tested. In practice, it is tested as far as possible at the manufacturer s works but often not leak-tested on-site. Reference 32 reviews the fuel leaks that have occurred, including a major explosion at a CCGT plant in England in 1996 due to the explosion of a leak of naphtha from a pipe joint. One man was seriously injured, and a 600-m chamber was lifted off its foundations. The reference also reviews the precautions that should be taken. They include. selecting a site where noise reduction is not required or can be achieved w ithout enclosure. If enclosure is essential, then a high ventilation rate is needed it is often designed to keep the turbine cool and is far too low to disperse gas leaks. Care must be taken to avoid stagnant pockets. 

Finally, noise is also becoming of increasing concern, particularly on sites adjacent to urban areas. Acoustic enclosures, supplied by the manufacturer, will normally reduce noise levels to 85 dB, but if further reduction is required, attention must be paid to the material used to construct the buildings and enclosures low noise levels can be achieved only at a cost. 

Feedwater pumps will not normally constitute a noise problem unless the area is particularly sensitive. Two alternatives are then available. One is to install reduced-speed pumps and the other is to site the pumps in a separate acoustic enclosure within the boiler house. Oil-circulating pumps are usually low speed and, as such, do not cause a noise problem. 

That the authorities have refused unreasonably to accept compliance with alternative requirements or that the requirements of the notice are otherwise unreasonable in character or extent, or are unnecessary. This defense is self-explanatory. The local authorities are only permitted to ask for works that will abate the noise nuisance. Other works (perhaps to comply with legislation) should not be specified in the notice. They may, however, be contained in a letter separate from the notice. An example of this would be where the fitting of acoustic enclosures to food-manufacturing machines breached food hygiene requirements. Readily cleanable enclosures may be a requirement of the Food Hygiene Regulations, but it should not be contained in a Section 58 Control of Pollution Act notice. 

The first of these can he reduced hy suitable siting of the plantroom, anti-vihration mounting and possible enclosure of the machinery Air flow noise is a function of velocity and smooth flow. High-velocity ducts usually need some acoustic treatment. 

To quiet a noise-generating mechanism, the first impulse is often to enclose it. Sometimes an enclosure is in fact the best solution, but not always. If it can be determined what is causing the noise, appropriate action can be taken to be more specific and provide a cost-effective fix. In some cases the problem is caused by a component such as a stepper motor or gear set that does not produce objectionable noise by itself. The trouble typically develops because a small noise is transmitted to a metal frame or cabinet that then serves to amplify the sound using a plastic cabinet can isolate the noise problem. 

Distance is a major factor in reducing nuisance noise and suitable spacing should be considered in the plant initial layout. The acceptable amount of noise generation should be specified on the purchase order for the equipment. Where sound levels cannot be alleviated by purchasing a different make of equipment, sound attenuation devices should be fitted (i.e., enclosures) as an alternative. 

The Waterloo Barrier does not remediate wastes. The contaminant plume must be small enough for enclosure to be practical. The vibration and noise associated with pile driving equipment may be a problem in densely populated areas. Funnel-and-gate system can be problematic because they alter groundwater flow. In bouldered terrain and very dense unconsolidated sediments, the use of sheet piling may not be possible. Steel sheet pile applications are generally restricted to depths of less than 30 m. At some sites it is necessary to seal the barrier system to bedrock. 

Natural crystals often have enclosures containing gases or colourless liquid. The walls of the cavities are parallel to the faces of the cube. The liquid is usually an aq. soln. of brine, and the gases often confined under considerable press, usually hydrocarbons. When such crystals are dissolved in water, the gas escapes with a crackling noise when the cavity walls have become so thin that they cannot withstand the internal press. When the salt is heated, too, the expansion of the gas or liquid in the cavities bursts the mass, scattering the fragments in all directions. 

A metal enclosure or surface intended to prevent noise from interacting with a susceptible piece of equipment. Shielding may be applied at the source (if the source is known) or at the susceptible equipment. Figure 7.5 illustrates the two modes of shielding. 

Because the basic fuel cell needs no mechanical drive, its operation is quiet and involves no frictional losses (Figure 2.100). These characteristics should make it possible to locate them near the final user, producing a more even distribution of the generation capacity. Auxiliaries, particularly fans and blowers, must be quiet therefore, they should be well supported to prevent their motion and be provided with variable-speed drives. In addition, the feathering of the blade edges and the use of noise-reducing enclosures are recommended. 

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