The spectrum of fan noise is a composite spectrum, which is the superposition of the blade through frequency and the composition of the broadband aerodynamic noise. The blades are determined by the following frequency:
In the fn=Nbn/60 khz type:
Number of B-----Blades
N-----fan rpm, turn/Sub
n-----homophonic ordinal number: n=1 (base frequency), n=2 (second homophonic)
The sound level of the blower noise relates not only to the structure of the blower, but also to its working state (determined by the total pressure and air volume). Different series, different models of fans, the sound level is not the same. The same fan, under different operating conditions, its sound level is also different. When the blower works at the highest efficiency point, the sound level tends to take low values.
In order to characterize the noise performance of the blower, the concept of the Class A is presented. A sound level is the one that is generated by the ventilator in the unit flow (1 meters/sub) and the unit full pressure (1 mm water column). The same fan is different in different working conditions than a sound level. At the highest efficiency point, lower than a sound level. The different series of fans in rated operating conditions of a sound level characterized the series of wind turbine noise level and product quality. So at home and abroad more than a sound level as a fan noise limit indicator. The same series of different types of fans, the sound level of a similar. The higher the machining precision of the blower, the better the aerodynamic performance, the lower the sound level than a.
In general, the front vane centrifugal fan, compared with a sound level below 2dBA; rear vane centrifugal fan, lower than 30dBA wing-type blade centrifugal fan, below 25dBA; axial fan, less than 38bBA. Under different operating conditions, the sound level of the ventilator noise is determined by the following:
A sound level of the inlet (or vent) of the La----blower, DBA;
Lsa----fan Inlet (or vent) than a sound level, DBA;
Q----air volume, meter 3/cent;
P----fan full pressure, millimeter water column.
The common method of controlling fan noise is to install a resistive muffler at the inlet and outlet of the blower. For the occasions with higher noise reduction requirements, the sound insulation box can be used, and the shock absorber is arranged between the unit and the foundation. By adopting the above method, the obvious noise reduction effect can be obtained.
Domestic now has a lot of noise control equipment factory, can provide all kinds of fan noise, sound insulation box and shock absorber. The noise problem of fan, technically speaking, has been effectively controlled in our country, and the low noise blower has begun to appear. However, for the special requirements of the fan muffler, such as requirements waterproof, moisture-proof, high temperature or dustproof, there is still a lot of research work worth carrying out.
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