"220V AC Cooling Fan" impeller modal vibration form mainly by four blades week to various combinations of vibration, resulting mainly for this reason is forward-swept blade stiffness is much smaller than the hub stiffness that blade "soft", and the hub of "hard "; leaf blade low frequency vibration modes mainly dominated overall torsional pendulum, but mainly in the high-frequency wave-based blade bending. From the impact of "220V AC Cooling Fan" think big in terms of noise before the sixth-order mode effects, because of its place as a result of the flow field has a greater impact, resulting in a change in the angle of attack of the blades into the air, thus forming the blade surface fluctuations in the lift, the most serious cases will have galloping, have a greater aerodynamic noise and great efficiency. Understand the reasons "220V AC Cooling Fan" axial fan noise generation. I believe we can use the process of attention.