"DC Fan" refers to the speed of the fan rotation speed, the number of turns is usually 1 minute to measure the rotation, namely: rpm. Electromechanical speed and number of turns, diameter, bottom diameter and the outer diameter of the impeller blades, blade shape and the bearings and other factors, the speed increases, the air volume increases. The case of the size of the speed value, to a certain extent, represents the size of the wind, the condition is constant, the greater the speed, the noise and vibration will be increased accordingly. Therefore, the amount of wind to meet the cooling requirements, should try to use low-speed fan.