"Waterproof Cooling Fan" distinguish Powerful and silent type is not too strict, but the same size, the same voltage for computer fans, air pressure and noise will always be two irreconcilable contradictions. Fan speed is the number of revolutions per minute fan fan page, the unit is rpm. "Waterproof Cooling Fan" motor speed is determined by the number of turns in the coil, voltage, number of fans fan page, inclination, height, diameter and fan bearing system. In the case of the fixed structure of the fan, DC fan (i.e., the use of a DC fan) with the speed of change of the operating voltage changes in synchronization. "Waterproof Cooling Fan" can be carried out by the speed of the internal speed signal measurement can also be measured (external measurement is to measure the speed of the fan with a special red line speedometer conducted by external, internal measurements directly to the BIOS can see, you can also software to see internal measurement error is relatively larger).