Noctua NF-B9 PWM Cooling Fan Beveled blade tips reduce critical rotor/ stator interaction, combine a higher blade surface area with quieter operation and form a cornerstone of the fan's efficiency. Vortex-control notches split up trailing edge vortices and spread the fan's noise emission over a wider range of frequencies. Supporting fully automatic speed control, the NF-B9 uses Noctua's novel, custom-designed NE-FD1 IC that integrates Smooth Commutation Drive (SCD) technology. The NF-B9 PWM is supplied with a Low-Noise Adaptor (L.N.A.) that reduces the maximum fan speed from 1600 to 1300rpm. The L.N.A can run the fan at a fixed speed of 1300rpm or cap the maximum speed when using automatic control.