We all know that "Small Cooling Fan" features mainly reflected in long life, high reliability; smooth performance, run; intelligence, mechatronics, easy to control; small size, low power consumption; low noise, no electromagnetic interference. When the temperature changes slowly cooling fan, cooling fan speed changes are slow, will not suddenly change "Small Cooling Fan" speed and noise. The reaction time depends mainly on the length of the sensor of its thermally-induced sensitivity. Therefore, the speed of the cooling fan speed control is mainly based on the temperature difference between the heat sink induction passed automatically adjust. Should be at the same air volume, a large fan operating noise at a lower speed is less than "Small Cooling Fan" operation noise at high speed. Another factor is that we tend to ignore the fan bearings.