Mindblown: a blog about philosophy.
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Automobile and Truck Noise Sources and Control
In cars, trucks, and busses, major power plant noise sources include gasoline and diesel engines, cooling fans, gearboxes and transmissions, and inlet and exhaust systems. Other major sources include tire/road interaction noise and vibration and aerodynamic noise caused by flow over the vehicles [1]. (See Figure 14.1) Although vehicle noise and vibration have been reduced over…
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Introduction
The number of vehicles on the road continues to increase worldwide. Road traffic noise is really a greater problem than aircraft noise in most countries since it affects many more people. The noise of railroad and rapid transit vehicles is also a problem for people living near to rail lines. Noise and vibration sources in…
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Radiated Noise
Although one is often more concerned with air noise emanating from grilles and diffusers in an occupied area, careful consideration should also be given to noise which may be radiated directly from the outer casings of various system elements conveying air to or from the grille. For example, although ducts and mixing boxes are often situated…
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Sound Generation in Mechanical Systems
In high‐velocity systems, the flow of air through the various elements (such as ducts, elbows, take‐offs, mixing boxes, and grilles) can produce high noise levels. This type of flow‐generated noise is often neglected by system designers who are later surprised to find that some areas of a building are much noisier than they had estimated…
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Sound Attenuation in Ventilation Systems
Many of the elements which make up a typical ventilation system are capable of providing some degree of sound attenuation. It is, therefore, very important to be able to estimate this attenuation in order to ensure acceptable acoustical conditions in all the areas to be served by the ventilation unit. This implies that there should…
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Vibration Isolation of Ducts, Pipes, and Wiring
Because a machine mounted on vibration isolators is subjected to large amplitude motions, all connections to the machine from piping, wiring, and ductwork should be flexible enough so as not to restrict the movement of the machine or allow significant amounts of noise and vibration to pass through the connections into the building structure. In…
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Selection of Vibration Isolators
The theory of vibration isolation presented in Chapter 2 shows that in order to reduce the magnitude of the force transmitted by an isolator to its support, one has to choose its natural frequency, fn, so that the ratio of the forcing frequency to the natural frequency, (f/fn) is much greater than . This means that for most air‐conditioning…
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Vibration Control of Equipment
Since vibration in the audible frequency range can easily be transformed directly into noise, or propagated to some other part of the building and then radiated as noise, it is of extreme importance to control all vibration in the mechanical room to within tolerable limits. Ideally, the mechanical room should be located well away from…
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Use of Floating Floors
After the sound pressure levels within the mechanical room have been adequately and economically reduced, the next step is to introduce a massive layer between the room and the nearby critical areas. The primary purpose of this massive layer, normally called a floating floor, is to reduce airborne transmission through the floor rather than reduce vibration…
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Mechanical Room Noise and Vibration Control
If the mechanical room is located on the ground floor of a building, transmission of noise and vibration through the floor is normally not a problem. However, care still needs to be taken to prevent noise and vibration propagating into adjacent spaces. Figure 13.29 shows a ground floor mechanical room where the intake air flow passes through…
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