Noctua NF-B9 92mm Fan (31 CFM)

Bevelled Blade Tips
Due to advanced design measures like the bevelled blade tips, the NF-B9 is surprisingly quiet despite its outstanding airflow and pressure performance.

Vortex-Control Notches
Psychoacoustic optimizations like the Vortex-Control Notches make the NF-B9's noise pattern more pleasant to the human ear.

Smooth Commutation Drive
The new SC drive system reduces torque variations and thereby ensures improved running smoothness, particularly at lower speeds.

Self-stabilizing oil-pressure bearing
Noctua's well proven SSO-Bearing technology guarantees supremely quiet operation and exceptional long-term stability.

NF-B9 Blade Design
Employing advanced noise-reduction techniques like Beveled Blade-Tips and Vortex-Control Notches, the NF-B9's highly-optimized blade design provides superior pressure and airflow performance at extremely low noise levels.

By increasing the distance between the impeller and the frame at the outermost areas of the fan where the impeller achieves the highest velocities, beveled blade tips help to reduce critical rotor-stator interaction. This measure makes it possible to combine the large blade surface area and high profile chord length of a high-output blade geometry with excellent quietness of operation.

Basically, an increase in static pressure usually brings about higher noise emissions. In the case of the NF-B9, this problem is dealt with by adding Vortex-Control Notches to the blades' trailing edges. Due to the two notches at the trailing edge, the flows along the suction and pressure side mix more smoothly. This allows for less turbulence and velocity loss, which leads to a significant reduction in noise emission as well as increased efficiency. In order to achieve the smoothest possible transition and maximum noise reduction, the Vortex-Control Notches are rounded in shape.

In addition to optimizing the joining of the flows at the trailing edge, the Vortex-Control Notches fulfill the task of psychoacoustic optimization: Due to the Vortex-Control Notches, trailing edge vortices are split up into several smaller vortices. Thus the noise is spread over a wider range of frequencies and therefore perceived as much less annoying.

Smooth Commutation Drive (SCD)
Next to aerodynamic noise and bearing related noises, the so called "commutation noise" or "switching noise" can play a major role in the noise emission of axial fans with brushless DC motors. At each transition from one stator coil to another, the rotor receives a sudden torque pulse when the next coil switches on. Each of these torque pulses causes a minute deformation of the whole fan structure. Depending on rpm, torque and the material of the fan, this can result in noticeable noises. Noctua's Smooth Commutation Drive system provides more continuous switching in order to achieve a smoother transition between the stator coils and thereby significantly contributes to the fan's overall quietness.

SSO-Bearing
Thanks to an optimized principle of operation, the self-stabilizing oil-pressure bearing (SSO bearing) of the Noctua NF-S12 and NF-R8 series surpasses current types of ball, sleeve or liquid bearings in terms of long-term stability and quietness.

SSO Principle of Operation
The rotary motion of the axis generates pressure upon the special oil enclosed within the bearing. This causes the build-up of a dynamic pressure field that centers and stabilizes the axis within the bearing shell. While conventional liquid bearings employ the principle of hydrodynamic pressure too, the SSO bearing is equipped with an additional magnet that supports the self-stabilization of the rotor axis. This allows for a faster, more precise and more reliable centering of the rotor axis and thus increases the long-term stability and quietness of the bearing: When the fan starts, the dynamic pressure field of the liquid bearing needs to build up first, which results in an initial precession of the axis, the so called gyro effect. This amounts to an increased abrasion until the axis is stabilized through the build-up of the dynamic pressure field, which may by and by lead to increased noise emission and bearing defects. Because of this, the SSO bearing possesses a built in magnet, whose field ensures the immediate self-stabilization of the rotor and hence reduces the gyro effect. In addition to the stabilization during the start-up phase of the fan, the supporting magnet allows for a more exact centering of the axis within the bearing shell and thus further reduces bearing resistance, abrasion and noise emission.

SSO Compared to Conventional Sleeve and Ball Bearings
The sleeve and ball bearings currently predominating the fan market exhibit major drawbacks: While conventional sleeve bearings initially have very low noise emissions, they mostly possess unsatisfying long-term stability, which leads to a short overall lifespan and increasing noise after longer operating times. High grade ball bearings, on the other hand, while providing satisfying long-term stability operate at slightly higher noise levels from the beginning. The SSO bearing not only surpasses the quietness of conventional sleeve bearings but also the long-term stability of current top-of-the-line ball bearings.