Acoustics Ventilation noise

Ventilation noise originates primarily from fans and the air turbulence generated inside ducts and around supply air and exhaust air terminal devices. The appearance of the noise is, of course, affected by factors such as the speed of rotation and the power of the fan, and by how the fan is stabilized or in other ways acoustically insulated. The noise level and the frequency characteristics are also largely derermined by the velocity of the air inside ducts and around terminal devices, where factors such as the dimensions and appearance of the ducts and terminal devices may play a decisive role in the appearance of the noise. 

The subject of acoustics involving sound transmission is of prime importance in industrial ventilation. Correct system design will ensure that the designer provides a system that will not give rise to complaints regarding noise levels. 

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. 

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. 

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. 

Recovery area. Because of the presence of noise and dust the machinery should be located in an enclosed area, acoustically insulated and with good ventilation. Antivibration mountings should be used for all equipment and protection provided for nose, ears and throat of all personnel who have to be in the environment. It is also advisable for some form of metal detection and separation equipment to be included in the recovery cycle. 

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