"The Zerotherm CF900's Protechnic MGT9212HS-S25 fan has a thermistor attached to a short length of wire coming out of the motor hub, and this plays a crucial role in how the heatsink performs. The thermistor is cleverly located inside a well formed within in the array of copper cooling fins, so it accurately responds to the temperature of the metal, not the internal case air temperature. This enables the Zerotherm CF900 fan to scale its impeller speed as necessary, and cuts down on unnecessary noise. At its slowest speed (800RPM), the 95mm diameter Protechnic fan barely produces 35 dBA noise. At its full speed of 2300RPM, the fan rumbles away with a moderately audible 48.3 dBA."