"The NF A15 PWM, A14 FLX and the A14 ULN premium fans share many of the same features. At the heart of the NF series is the SSO2 bearing. SSO2 is a second generation metal bearing design that moves the rear magnet closer to the axis. This allows for an overall increase in stabilization and precision while extending the lifespan of the bearing. The AAO or Advanced Acoustic Optimization frame designed by Noctua allows these fans to combine several enhancements that increase performance and lowers the noise produced by the blades."



Link: Neoseeker