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| Noctua NF-R8 & NF-S12 Fans |
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| Written by Mikhail Ivanenkov | |
| Tuesday, 24 July 2007 | |
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The Straight-Blade-Design of the NF-S12 series provides the maximum efficiency of a straight fan blade without the drawback of higher noise emission, which arises when straight blades are used at higher rotation speeds. At the low rotation speeds of the NF-S series, the Noctua Straight-Blade-Design achieves a significantly higher flow rate than forward or backward swept blade designs. Furthermore, among other measures to prevent vortices like the rounded rotor hub, the distance between rotor and stator (tip clearance) was increased in order to reduce the problem of tip vortices which plays an important part in the noise emission of axial fans. With its fan blade exactly tailored to ultra low noise application, the NF-S12 series is significantly quieter than other high end silent fans.
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.
The sleeve and ball bearings currently dominating 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. Testing was subjective as I don't have equipment to accurately measure airflow and noise levels just yet. What I did was go into an empty room, connect the fans to a shorted (via pins) passive power supply and listen. At basic speeds (no resistors), both fans are very quiet. At about a foot away, they can still be heard but not by much. At 3-4 feet they're almost inaudible. With the LNA, the 120mm fan is barely audible at 1 foot and inaudible at 3-4. The 80mm is slightly louder. With the ULNA, both fans are inaudible at 1+ feet. However, the 80mm fan refused to start up with the ULNA. Perhaps there wasn't enough initial power (too much resistance), but it just wouldn't start spinning unless I gave it a little push. Then it would work fine. Obviously this would be a problem if it were installed in a case. Then again, I don't see why anyone would want to run the NF-R8 with the ULNA anyway since the airflow at that point is so low it might as well be nonexistent. Both fans worked fine with the LNA. I'm not sure why Noctua decided to package both resistors with the 80mm fan and only one (ULNA) with the 120mm fan. The latter would make more use of both it seems. Pros
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| Last Updated ( Tuesday, 24 July 2007 ) |
