At a fixed "220V Cooling Fan" structure, the DC fan (that use DC fans) the speed of change of the operating voltage synchronous changes. The fan speed can be measured by the internal speed signal can also be measured (external measurement is to measure the speed of the fan with a special red line tachometer, internal measurements directly to the BIOS can see, you can see the outside via software Internal measuring relatively large number error). "220V Cooling Fan" axial fan speed and cooling capacity and not necessarily related to a higher fan speed but will bring more noise, if the wind is almost the amount, you can choose when to buy low speed cooling fan product "220V Cooling Fan", when in use quieter.