Silent 120mm PWM System Fan with Quad Air Inlet Technology. Proprietary Quad Air Inlet system features four strategically placed aerodynamic air inlet that allows for extra air intake. HPLN (High Precision Low Noise) bearing system, offering stable and precision rotation eliminating excess vibration and noise. Four pin Pulse Width Modification (PWM) RPM spin speed control ultra wide range RPM settings. Roughly 34% more selection range than the system fans from competitors. *some RPM speeds are only available through PWM control. Integrated Vibration Absorbers built in, nullifies fan vibration. Ultra low RPM speeds of 200~1000 RPM with the minimum noise level of 5 dBA.