Noise acoustic enclosures

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. 

Noise level (when operating at rated capacity) this should be below 70 dB at about 2 m from the blower. In case of higher noise, an acoustic enclosure will be required, which will add to the cost. 

Noise level at full load operation should be less than 60 dB. Otherwise a separate acoustic enclosure as per statutory instmctions will be required. 

The two major methods of personnel protection are the provision of a quiet room or peace haven, and the wearing of ear-muffs or ear-plugs. The peace haven is similar in construction to an acoustic enclosure, and is used to keep the noise out. Ear-muffs or ear-plugs should be regarded only as the final resort to noise control. Their selection should be made with care having regard for the noise source, the environment and comfort of the wearer. 

Noisy machinery is sometimes placed inside a small containment building or acoustic enclosure. Acoustic enclosures may be either of the close fitting or walk-in (large) type. The use of acoustic enclosures is generally not a preferred solution to noise problems because they create a confined space and have the potential for a buildup of a flammable or explosive cloud should the equipment leak. Also, the containment structure is likely to make maintenance and inspection more difficult (a confined space entry will be required), and it will increase the size of the equipment s footprint. 

Mills Acoustic enclosure of the mill shell obstructs heat dissipation and makes inspection difficult, i. e., is not satisfactory. Boltless liner plates on rubber backing, or rubber liners, do not sufficiently reduce noise emission. A commonly employed and generally satisfactory solution is as follows Whole grinding plant with all its noise sources (mill, drive, air separator, conveyors, elevators, filters, etc.) accommodated in a closed sound-insulated building with central control room for operators and with additional ventilation (see Funke, 1969 and 1973, Techn. Merkblatt, Bundesverband der Deutschen Kalkindustrie, 1975). 

Machinery enclosures Walls of acoustic enclosures should consist of heavy but flexible panels lined internally with sound-absorbing material. Adequate ventilation, demountability of the enclosure for repairs, and arrangements for operating and/or observing the machine to be provided. If hot gas fans are acoustically enclosed, the surface of the fan casing should additionally be heat-insulated. For information on design and performance of enclosures for noise control see VDI2711. 

Drilling machines (rock drills in quarry) Acoustic enclosure of drive units and hydraulic equipment, as on compressors used on construction sites. Noise-suppression covers and silencers for exhaust air outlets of hammer drills. Sound-insulated control cabs (see Funke, 1973). 

Noisy machines should be accommodated in different rooms from quieter ones. Special acoustic enclosures for machinery with particularly high noise emission levels. 

The structure-borne noise generation and transmission of stiffened and interconnected structures under random loads is presented. The method is based on the transfer matrix for the stuc-tural response and on the modal decomposition for the interior acoustic field. The acoustic enclosure is taken to be rectangular in shape of which portion of the boundaries are elastic while the remaining surface is acoustically rigid. Numerical results are presented for a variety of acousto-structural problems. 

Consider a rectangular acoustic space occupying a volume V = abd zis shown in Fig. 1. The interior surface of the enclosure is assumed to be covered with absorptive materials for which the impedance characteristics are specified. Noise is generated in the acoustic enclosure through the vibration of the flexible portions of the side-walls, the partitions or the sound sources located in the interior. The perturbation pressure p within the enclosure satisfies the linearized acoustic wave equation... 

For the calculation of noise transmission into the enclosure, a simplified model shown in Fig. 4 has been chosen. A cantilever box beam is attached to two stiffeners of the discretely stiffened sidewall. A random point couple is acting at the free end of the cantilever beam. The walls at z 0 and z = d of the acoustic enclosure are treated with absorbtive materials which are represented by the point impedance model as... 

Somid-absorbent linings are frequently fitted in acoustic enclosures to reduce the buildup of reverberant noise inside the enclosiu-e. IVpical reductions in the reverberant noise level may be between 3 and 10 dB depending on the application. An additional benefit is the increase in transmission loss of the enclosure panel, which further reduces the noise level outside the enclosure. 

Gas turbines are a significant noise source and environmental pressures often dictate their installation within acoustic enclosures. The release of fuel within the enclosure is potentially hazardous if the release results in a volume of flammable fuel/air mixture within a significant fraction of the chamber volume. The release may be of gas, such as natural gas, flashing liquid such as propane, or liquid such... 

Noise and Noise Measurement (see Acoustic Enclosures, Turbine)... 

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. 

A loss control measure against identified risks by segregating the identified hazard to a specific (remote) location to protect the surrounding area from its effects and vice versa. Examples include placement of a chemical plant or process in a remote location and enclosure of an individual in an acoustic booth or enclosure to protect against noise exposure. 

There are a variety of control techniques, documented in the literature, to reduce overall worker exposure to noise. Such controls reduce the amount of sound energy released by the noise source, divert the flow of sound energy away from the receiver, or protect the receiver from the sound energy reaching him or her. For example, types of noise controls include proper maintenance of equipment, revised operating procedures, equipment replacements, acoustic shields and barriers, equipment redesign, enclosures, administrative controls, and personal protective equipment. 

Enclosures which give an attenuation of between 10 and 30dBA are the most satisfactory solution since they will control both the direct field and reverberant field noise components. In enclosing any source, the provision of adequate ventilation, access and maintenance facilities must be considered. A typical enclosure construction is shown in Figure 20. W. The main features are an outer heavy wall with an inner lining of an acoustically absorbent material to minimise reverberant build-up inside the enclosure. An inner mesh or perforate panel may be used to minimise mechanical damage. 

Acoustic control identification of sources of noise enclosure of noise muffling re-design of noise producing parts. 

Compressors, pumps Vibration-isolated mounting in enclosed soundproofed rooms. Machines preferably separated from one another by partitions or with individual enclosures. Ventilation or air intake openings of such rooms should have louvred sound attenuators. Intake and outlet silencers for the compressors. Pressure pipelines to have sound-damping expansion joints and acoustically sealed wall inlets. Pressure release pipelines to have silencers. Additional sound insulation for compressed air pipelines to suppress rushing noises. Sound-insulated enclosed portable compressors represent the current "state of the art" for use in quarrying operations. 

Figure 3.5.10 Noise enclosure. (Above) cross-section through typical noise enclosure wall (below) noise enclosure with access doors removed (Courtesy Ecomax Acoustics Ltd)...

Equipment enclosures are structures that surround the noise source and thus contain the sound it generates. However, enclosures can cause a buildup of high-level acoustic energy within themselves. Enclosures therefore usually consist of a wall with surface weight chosen to provide the required attenuation and an inner lining of porous material to dissipate the buildup of acoustic energy. In some cases where complete enclosures are built, the machines inside may require placement on vibration-isolator devices that prevent the transmission of structureborne noise to the outer surfaces of the enclosure. 

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