"Axial Flow Fan" in addition to the cooling effect of the fan noise at work is widespread concern. Fan noise is the noise generated when the size of the security equipment cooling fans work, influenced by many factors, in decibels (dB). When measuring the noise of the fan needs to be less than 17dB noise silencing chamber for the distance of one meter the fan and the fan shaft are aligned in the direction of the fan air intake port, using measured A-weighted manner. The spectral characteristics of the fan noise is also very important, so we must also use a spectrum analyzer records the fan noise frequency distribution, the general requirements of the fan noise to be as small as possible, but can not exist different tone. "Axial Flow Fan" noise and friction, air flow related. Fan speed, the greater the amount of wind noise caused by the greater will be another fan's own shock factor can not be ignored. Of course, fans of high-quality shock itself will be very small, but the front two who is difficult to overcome. To solve this problem, we can try to use larger size fan. Should be under the same amount of wind, the large fan working noise at low speed is less than a small fan operating noise at high speed. Another factor is that we tend to ignore the "Axial Flow Fan" bearings. Since the fan rotates at high speed friction between the shaft and the bearing to the collision, it is also a major source of fan noise.