"220V Cooling Fan" will produce the blades rotate with air friction or impact occurs. It will produce the blades rotate with the air friction or impact occurs. The faster the speed, the higher the frequency of air access solution, its noise is more acute. The faster the speed, the higher the frequency of air access solution, its noise is more acute. "220V Cooling Fan" width or thickness of the blade of the increase, this phenomenon is more pronounced. Increasing the width or thickness of the blade, this phenomenon is more pronounced. Frequency noise is compounded by a variety of frequencies, these frequencies are concerned with the speed of a fan. "220V Cooling Fan" frequency noise is a composite made from a variety of frequencies, these frequencies are concerned with the speed of a fan.