Noctua 60x25mm PWM A-Series Blades with AAO Frame, SSO2 Bearing Premium Cooling Fan NF-A6x25 PWM The NF-A6x25 impeller features suction side Flow Acceleration Channels. By speeding up the airflow at the crucial outer blade regions, this measure reduces suction side flow separation and thus leads to better efficiency and lower vortex noise. Thanks to its streamlined, compact motor design, the NF-A6x25's motor hub is smaller than with conventional 6cm fans. This allows for more blade surface area and thus contributes to the NF-A6x25's superior airflow and pressure performance. Noctua's AAO (Advanced Acoustic Optimization) frames feature integrated anti-vibration pads as well as Noctua's proprietary Stepped Inlet Design and Inner Surface Microstructures, both of which further refine the fan's performance/noise efficiency. Integrated Anti-Vibration Pads made from extra-soft silicone minimize the transmission of minute vibrations while maintaining full compatibility with all standard mounting systems and fan clips used on heat sinks The NF-A6x25 features the further optimized second generation of Noctua's renowned, time-tested SSO bearing. With SSO2, the rear magnet is placed closer to the axis to provide even better stabilization, precision and durability. The NF-A6x25 PWM is supplied with a Low-Noise Adaptor (L.N.A.) that reduces the maximum fan speed from 3000 to 2300rpm. The L.N.A can be used either to run the fan at a fixed speed of 2300rpm or to cap the maximum speed when using automatic PWM control. Noctua Stepped Inlet Design add turbulence to the influx in order to facilitate the transition from laminar flow to turbulent flow, which reduce tonal intake noise, improve flow attachment & increase suction capacity Supporting fully automatic PWM speed control, NF-A6x25 PWM uses Noctua's custom designed NE-FD1 PWM IC that integrates Smooth Commutation Drive (SCD) technology.