Noise And Vibration Control !!INSTALL!!
Noise and vibration in a building are either caused by the building elements directly, as in the case of mechanical system noise, or allowed to affect the building from outdoors, as in the case of automobile or air traffic noise. Reverberation in enclosed spaces is also an important acoustical parameter determined by room shape, finish selections, the room size, and the number of people in the space.
Noise and vibration control
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The responsibility for the acoustical environment falls squarely on the building design team, requiring attention to noise sources, such as mechanical, electrical, and plumbing (MEP) systems, as well as architectural elements that both enclose spaces and isolate noise.
Four key terms are discussed: noise, vibration, reverberation, and speech intelligibility. These are the basic acoustical human-comfort parameters, just as temperature, humidity, and air movement are basic human-comfort factors for mechanical system design.
Other vibration sources can be human, such as footfall noise on hard floors or moving tables and chairs in a ballroom above an office area. Vibration also can be caused by external sources, such as nearby trains or other heavy equipment outside the building.
Perceptually, vibration may be lower in frequency as compared with audible sounds, usually being below about 20 Hz (cycles per second). Vibration also can be in the audible frequency range of roughly 20 to 20,000 Hz and radiate from the structure as airborne noise.
Noise and reverberation affect speech intelligibility, which is a measure of how well words are heard between a talker and a listener in a given environment. We increase speech intelligibility when we reduce reverberation and noise.
Reverberation is reduced when a space has more absorptive surfaces, such as acoustical tile ceilings, carpeted floors, and fabric-wrapped fiberglass acoustical panels. The role of reverberation in the acoustical environment is complex; this article will focus more on noise and vibration control.
In any building or space design, the scope of work for noise and vibration as well as the related architectural elements should be determined early in the design process. Just like waiting to start the mechanical system design during the contract-documents phase after the building design is almost done would be a disaster, waiting to address acoustical issues too late in the process can have similar consequences in terms of both added cost and decreased occupant comfort.
There are, of course, other special goals that are variations or combinations of these three goals. One example is creating functional open-office spaces, where the increasing background noise and reducing the intelligibility of speech can be the goal. Even these specialty goals involve parameters associated with the basic three noted.
With goals established and scope of work defined, the design work begins. At the beginning of a project, noise- and vibration-control goals can play an important role in determining space adjacencies. As the project design progresses, more detail is developed that requires integration into the deliverables for each building trade, particularly architecture, interior design, and the MEP trades.
Vibration criteria is tied to NC, in that structure-borne noise radiated from building elements should not produce audible sound beyond the airborne NC for any given space. Vibration isolation also is intended to reduce vibration that can be felt but is below the audible spectrum. To that end, ASHRAE includes a definitive and long-standing set of recommendations for selecting the type and performance of vibration isolators based on the equipment being isolated and the structure on which it is supported.
In a new building, a tenant build-out, or even a renovation, the most cost-effective noise-control treatment is changing space adjacencies early in design. Significant time, money, and aggravation can be saved by taking noise control into account when planning space adjacencies. Locating a conference room or an office next to a mechanical room, for example, can have a huge impact on the design and the cost of the mechanical systems as well as architectural elements.
In this case, equipment can require additional vibration isolation, perhaps with the need for inertia bases for some equipment. Piping and ductwork may require additional vibration isolation. Ductwork may require rerouting with additional acoustically lined ductwork and silencers. Architecturally, special (and costly) wall or floor/ceiling constructions may be required to reduce airborne noise.
A supply-air fan makes noise, and the noise can propagate down the duct and into a room via a diffuser, which also makes noise, and through the air to an occupant. That noise also can radiate through its enclosure, through a wall or ceiling, and through the air again to the same or another occupant. The fans also produce vibration that enters the structure; travels in the floor, columns, and walls; and radiates yet again through air to another building occupant. All of these paths are addressed as part of the acoustical design process.
There are some common noise- and vibration-control treatments used to mitigate noise from the source to the receiver. These may be specific to a trade (like the use of duct-liner board in air ducts) or more generally applicable, as in the case of selecting appropriate space adjacencies. Architectural elements also can act as noise-control treatments including the use of enhanced construction of floor/ceiling assemblies, partition design, and alternative door and window materials and hardware.
After the noise- and vibration-control treatments noted above are developed and recommended, they are then incorporated into the design package. The acoustical input may appear in a variety of contexts in the design package including:
This UFC provides qualified designers the criteria required for design and construction of those features related to noise and vibration control of electro-mechanical, mechanical, ductwork, and plumbing systems most commonly encountered in government facilities.
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In this paper, the current state of the art on shunt piezoelectric systems for noise and vibration control is reviewed. The core idea behind the operation of electronic shunt piezoelectric circuits is based on their capability of transforming the dynamic strain energy of the host structure, i.e., a smart beam or plate, into electric energy, using the properties of the direct piezoelectric phenomenon and sending this energy into the electronic circuit where it can be partially consumed and transformed into heat. For this purpose, transducers which are made by piezoelectric materials are used, since such materials present excellent electromechanical coupling properties, along with very good frequency response. Shunt piezoelectric systems consist of an electric impedance, which in turn consists of a resistance, an inductance or a capacitance in every possible combination. Several types of such systems have been proposed in the literature for noise or vibration control for both single-mode and multi-mode systems. The different types of shunt circuits provide results comparable to other types of control methods, as for example with tuned mass-dampers, with certain viscoelastic materials, etc. As for the hosting structure, several studies on beams and plates connected with shunt circuits have been proposed in recent literature. The optimization of such systems can be performed either on the design and placement of the piezoelectric transducers or on the improvement and fine-tuning of the characteristics of the system, i.e., the values of the resistance, the inductance, the capacitance and so on and so forth. There are several applications of shunt systems including among others, structural noise control, vibration control, application on hard drives, on smart panels etc. Last but not least, shunt circuits can be also used for energy harvesting in order to collect the small amount of energy which is necessary in order to make the system self-sustained.
Damping is one of the most effective methods of controlling noise and vibration. It is a process that converts vibrational energy into heat, eliminating the vibrational energy through friction and other processes. Increasing damping or stiffness can both reduce resonant vibration and the resulting noise by preventing the vibration from travelling through the structure.
Rubber mounts with damping properties are often used in engine compartments, enclosures, cab walls, and floor and ceiling systems; additionally, they are beneficial for use in appliances, medical equipment, heavy equipment, and a variety of other applications. Materials used for damping must not only reduce noise and vibration but must be able to withstand heat. In this article, we will further explore the significance of damping and the techniques for noise and vibration control that manufacturers must take into account.
Appliances, heavy equipment, generators, and other mechanical structures are capable of producing a great amount of noise and vibration. Vibrational energy is problematic for a variety of reasons; it can make appliances such as washing machines, blenders, vacuums noisy and disruptive for users. Medical equipment can be uncomfortable, and in larger mechanisms, like engines, noise and vibration control may be needed in the engine compartments, enclosures, cab walls, and floor and ceiling systems. This is because vibrations cause instability and fatigue in mechanical structures in addition to creating excessive noise.
Free layer damping controls vibration and noise in products with surfaces that are at or near resonance and is best for lightweight structures. This is because free layer damping does add a significant amount of weight to your structure, meaning that it is not ideal for applications where limiting weight is a concern. 041b061a72