Category: (((—Acoustics Engineering—))))

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…

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…

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…

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…

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…

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…

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…

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…

The main acoustical goal should be to locate the major noise sources, mechanical equipment rooms (housing the AHU), cooling towers, chiller rooms and roof top and other package units as far as possible from noise‐sensitive areas in the building. In large buildings it is often necessary to locate the mechanical room in the core of…

It should be noted that the selection of a fan is based primarily not on its acoustical characteristics but rather on its ability to move a required amount of air against the installed static pressure created by the downstream system elements. The first cost of the fan, its size, and maintenance costs are of primary…