Sound enclosure

PPE (personal protective equipment) subteam This team can ensure that PPE requirements are defined for the different tasks within the plant and then conduct audits for compliance. When new equipment or processes are brought into the plant, they can assess the PPE required. Noise abatement subteam Annual noise level audits, annual hearing testing, and defining the need for sound enclosures would fall within the scope of this team. 

Sound level 70 db when the complete system is housed in a sound enclosure... 

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. 

Sound-Absorptive Blankets. Sound-absorptive blankets of fiber glass or mineral wool are not usually considered damping materials, but when fastened to sheet metal machine enclosures they can provide some useful damping in addition to sound absorption. 

Safety Standards (enclosures) for construction and guide for selection, installation and use of rotating machines Sound level prediction for insulated rotating electrical machines Energy management guide for selection and use of three phase motors Polyphase induction motors for power generating stations... 

Figure 7-6. An integral geared compressor driven by a motor with an open drip-proof enclosure. The enclosure also includes 85dba sound attenuation. Courtesy of Elliott Company ...

The high sound levels produced by an electric arc furnace can be contained within a furnace enclosure if a proper acoustical design is carried out. Any design should be checked by a competent acoustician. The following points should be considered ... 

Reverberation time The time required for a sound to fall to a given level in an enclosure. 

The degree of attenuation at the critical frequency can be very large, but this type of silencer has a very narrow bandwidth. This device may be suitable when the machine being dealt with emits sound predominantly of a single wavelength. Lining the chamber with absorbers can expand the absorber bandwidth of a Helmholtz resonator, but this has the effect of reducing the efficiency. The perforated absorber, which forms the basis of many acoustic enclosures and silencers, is a development of the resonator principle. 

As stated previously, packing the chamber with an absorber may broaden the bandwidth, but this lowers efficiency. It may be overcome by using multiple absorbers in the sound path, and placing a perforated sheet some distance away from the rigid outer wall of the enclosure and filling the cavity with absorber can do this. It is not necessary to use cross walls between the chambers so formed. In this case the equation becomes ... 

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. 

It was but a few minutes before the trumpets would sound. In our enclosure I looked over my horse, Belle Bete, and all our harness, as I have done a thousand times before and since. On such care for small things may a man s life rest, my father used to say in the stables, when I grew impatient as boys will with buckles and thongs, the proper care of leather and iron. Do not trust such care to any but yourself. When it was time to mount, I saw that the trappings over Belle Bete s chest hung crookedly, and the straps at his withers were differently fastened. Who has done this I asked. 

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. 

Unlike conventional explosives, which have instantaneous effects, chemical clouds take time to reach their target. This allows additional time to move out of the way or into a protective enclosure. In the case of civilians, anyone inside a soundly constructed house or car would almost certainly have full protection, even at distances as short as 50 meters, provided the doors and windows are closed. Putting duct tape and plastic over windows (or, as reported recently in one case, over the entire house) makes no sense. The blast effect of a warhead exploding closer than 50 meters would probably be more lethal than its contents of nerve gas. Furthermore, quick decontamination can prevent effects through the skin. Even ordinary clothing provides considerable protection. 

When a sound source is turned on in an enclosure, it excites one or more of the normal modes of the room. When the source is turned off, the modes continue to resonate their stored energy, each decaying at a separate rate determined by the mode s damping constant, which depends on the absorption of the room. This is entirely analogous to an electrical circuit containing many parallel resonances [Beranek, 1986], Each mode has a resonance curve associated with it, whose inxquality factor (Q) depends on the damping constant. 

At the present time, it is impossible to obtain an explosion-proof feeder. The feeder s electric coil can burn out causing sparking within the enclosure and possibly igniting powder or solvent vapors that have accumulated. To avoid this possibility, air purge systems are installed to prevent the buildup of explosive or flammable material. The air purge systems are also interlocked with the equipment so that in the event of lost air flow, the vibrator will be shut down and an alarm sounded. 

The main industrial control approaches include use of sound absorption, enclosures, barriers, and vibration isolation and damping. These methods are briefly described below. 

The vibration isolation of machine sources from their supports can be particularly useful in reducing the noise produced, especially if the machine is small compared with a large flexible support or enclosure that can act as a sounding board and radiate the sound. Soft metal springs or elastomeric isolators are often used as isolators. 

Optical flame sensors can be used for detecting the initial explosion, provided interference of environmental conditions can be reliably prevented. Pressure transducers are often used because the pressure wave travels at the speed of sound and can be detected at various angles. Vibrations and other mechanical movements can interfere pressure sensors. Therefore, efforts have to be made to minimize the influence of these interferences. The suppressant must be effective in flame quenching and compatible with product and the material of the plant. The suppressors must be designed and arranged adequately, so that the suppressant is rapidly and uniformly injected to the gas mixture in the protected enclosure. 

While not possible in some cases, a simple way to protect workers is either to increase their distance from the sound source or to put them in a soundproofed enclosure such as a control room or building. However, it is almost impossible to keep all workers away from high noise sources all the time, so hearing protection will probably be necessary. 

Reverberation persistence of sound in an enclosure after a sound source has been stopped. Reverberation... 

The maximum velocity of flow that can be attained is the speed of sound. It is reached for the critical pressure ratio Wi ji, and true as well if w < Wknt- The flow rate then only depends on the pressure inside the enclosure, pi, and not on the external pressure, p2. Equation (7.20) hence applies for discharge processes with velocities below the speed of sound and Eq. (7.23) for all other cases. The latter is usually required if gas under high pressure is discharged. 

The science of sound, including the generation, transmission, and effects of sound waves, both audible and inaudible. It may also refer to the physical qualities of a room or other enclosure (such as size, shape, amount of noise) that determine the audibility and perception of speech and music within the room. 

PWR Depression b. Concrete enclosure bulkheads c. RPV b. 25% degraded c. Little corroded sound b. 45% degraded c. 5% corroded - sound recovery purposes. Effectiveness of concrete corrosion barrier likely to be severely degraded. RPV remains intact. 

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