Nidec Servo Gentle Typhoon D1225C won’t lose to just any

Nidec Servo Gentle Typhoon D1225C (2150/12) details

Wondering how the Gentle Typhoon D1225C, the originator of the efficiently shaped rotor, is stacking up against much newer fans today? Very well. Outside the band of the most intense vibrations with annoying resonant frequencies, even from today’s perspective this fan has a top performance-to-noise ratio. In some ways it is even still unsurpassed, and the designers of the time built on strong physical foundations.

Explanatory note: In the context of this test, we always consider the “Nidec Servo Gentle Typhoon D1225C” fan to be the D1225C12B6ZPAA6 variant (i.e. with a max. speed of 2150 rpm at 12 V and without the rotor hoop, which the variants with speeds up to 3000 rpm and higher do have). In the following, the exact model designation is no longer given, and for unambiguous definition in the graphs, “2150/12” is in brackets, indicating the maximum speed/maximum voltage of the tested model. There is only one Gentle Typhoon with 2150 rpm at 12 volts with the Nidec Servo sticker.

The geometry of the Gentle Typhoon D1225C can certainly be described as timeless, it has become the inspiration for many modern fans. But at the same time, we don’t like to see new products described as “just another Gentle Typhoon” and hear that fan development has been stagnant for 15 years (since the Gentle Typhoon was released). It’s akin to blaming cars for having circular wheels – after all, those were already on medieval carriages and of all the options, it’s the best one, oval or polygonal wheels would work worse. And it’s similar with fans.

Inventing significantly different geometries from the Gentle Typhoon D1225C would always be a path to a worse result for the needs of PCs. You’ll see this in today’s tests, where the GT clearly beats many fans despite being a significantly older design. That’s why fan manufacturers with new models are resorting to these shapes and trying to perfect the details. Noctua has gone the furthest in this regard with the NF-A12x25 PWM, and by using a very strong material to construct the blades, they have eliminated the Gentle Typhoon’s main shortcoming, high vibration.

The advantage of a larger number of blades with a more pronounced curvature is that it does not push the air stream into the radial axis. And when it does, it does so to a much lesser extent than computer fans which can be described as standard, run-of-the-mill. That means seven wider blades with a smaller angle, with roughly equal sides (although the one at the motor is always a bit shorter) and with a smaller leading edge radius. The sweep and orientation of the airflow in these designs interferes more significantly with the radial axis and the trajectory is thus more conical. There would be nothing wrong with it in principle, but when the fan is seated in a tunnel, there is always more air friction at the level of the fan itself (under the frame arches) and more microturbulence at the sharp edges of the frame. That alone is a pretty significant handicap for the fan to achieve higher airflow at the same noise level.

If both designs were to reach their physical limits (you know that with fans it is not only the shape of the rotor or frame that matters, but also the strength of the blades or the properties of the bearings, the motor), it is often technically impossible for a fan with a rotor shape resembling the Gentle Typhoon to be noisier at the same airflow.

The Gentle Typhoon fan blades do have very similar proportional characteristics, including perhaps the same area per blade and also the same (or at least very similar) spacing, but there are a few differences as well. The GT’s blade tips aren’t as sharp (as the NF-A12x25) and it is also without the “acceleration” channels on the trailing side of each blade. In return, it has, further down near the motor housing, small serrations that reduce microturbulence and improve acoustic response at these points. Remarkably, Noctua used to use them as well, but phased them out of their designs, as did Fractal Design, for example.


The Gentle Typhoon D1225C is completely made from a composite of PBT, ABS and fiberglass (GF30), both rotor and frame. The material’s strength is lower and thermal expansion higher than LCP-based fans (these include the MSI MEG Silent Gale P12, for example, in addition to the NF-A12x25, of the models tested), so there is a larger gap between the blades and the frame in the GT compared to the NF-A12x25. It’s not a big difference though, it’s roughly a third, and again it doesn’t matter that much. The Gentle Typhoon has very high static pressure, and that’s also because of the proper thickness of the blades. Overall, this is a very sturdy fan weighing in at 198 g. Only the cable is more delicate, unbraided. It has the individual wires “loose”, without a mesh.

Since 2008, although the Gentle Typhoon D1225C initially carried the Scythe brand for a long period, its manufacturer was Nidec Servo. So it seems there were no changes in the design after the “separation” from Scythe. Manufacturing practices across time may have been somewhat different though. However, their effect on the fan’s performance will most likely be minimal.

One more important note about the bearings used. They are ball bearings, meaning robust, although compared to liquid (FDB, SSO2, etc.), especially at lower speeds, they contribute more to the overall noise of the fan. The mean time between failures is given by Nidec Servo as a function of temperature load. Desktops in homes should see 100,000 hours. But for more demanding conditions with typically higher ambient temperature, 45,000 hours at 60°C is quoted.

* When reading performance values, a certain amount of tolerance must always be taken into account. For maximum speeds, ±10 % is usually quoted, minimum speeds can vary considerably more from piece to piece, sometimes manufacturers will overlap by as much as ±50 %. This must then also be adequately taken into account for air flow, static pressure and noise levels. If only one value is given in a table entry, this means that it always refers to the situation at maximum speed, which is achieved at 12 V or 100 % PWM intensity. The manufacturer does not disclose the lower limit of the performance specifications in its materials in that case. The price in the last column is always approximate.

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Comments (15) Add comment

  1. GentleTyphoon is the name of a family of industrial axial fans designed and manufactured by Nidec-Servo

    The D1225C achieves an aerodynamic design that pushes the limits of material and injection mold engineering at a constrained cost (the material used for the fan blades is probably only half as stiff as the LCP material used by NOCTUA), and to mass produce fan blades with the potential for significantly improved performance at the same specification I think has until now been limited by the injection mold and process and material properties.

    One more thing, this seems to be the only 120mm axial fan I’ve seen with a removable motor stator – they are held in the bearing housing by springs and catches and are easy to maintain.

      1. Thank you for that comment, you obviously have that fan very well studied. I’ll admit that I was convinced that first those fans were at least designed by Scythe and then that brand was sold to Nidec Servo. But it is true that Nidec Servo also appears as the manufacturer on the labels of fans that still bore the Scythe logo.

    1. You’re right. We’ve adjusted the labelling in the charts to make it right.

      “Nidec Servo Gentle Typhoon D1225C12B6ZPAA6” is too long and we can’t fit it into the charts like this. But it’s true that after cutting even D1225C, it’s incorrect, although it’s clarified right at the beginning of this article (it would be unclear in the next ones, where this fan will appear in the graphs). So we compromised with “NS Gentle Typhoon DC1225C (2150/12)”, where the model designation in parentheses is the speed/voltage. That works out in the charts, and is now hopefully a pretty accurate and unambiguous designation for this particular fan. 🙂

      Of the 120mm fans, the Enermax Magma or even the recently released ThermalTake SWAFAN 12/14 have user level removable rotors.

        1. Now we’re clear, okay. We will also discuss the selected fans later at HWC. Especially with regard to examining bearings and things around them. Still, it’s a bit strange for fans with fluid bearings, for example, to have such a large variance in MTBF.

          1. Personally, I believe that in the vast majority of fans there is no real FDB, those “fluid dynamic” bearings are just an imitation of the marketing of the SPM bearings on the HDD, or essentially a variant of the original fan sliding bearings, and most of these bearings seem to be processed by low-temperature alloy, very fragile, but once the lubricant failure is easy to Failure.

            Currently, the only fan bearings I’ve ever disassembled that match the SPM bearings on the HDD are in the RTX4090 fan, complete with thrust bearings and the exact same structure and material as the HDD disk bearings, also from Nidec.
            Even so, I personally think it is unlikely that such a bearing will operate completely on the fluid dynamic pressure layer when working in the fan (unstable working conditions and too low speed).

          2. L10 is generally used for marking the life expectancy of fans in industrial environments.
            MTBF is actually a very ambiguous value, and manufacturers can be very flexible in their interpretation of it.

            But even the L10 value is not exactly the same across companies’ testing standards, and the life expectancy of a fan is very difficult to verify by a third party (just as the life expectancy of an HDD has long become an illusory value).

              1. Even when disassembled, there are many difficulties in assessing the life of a fan, such as the performance of the lubricant, the accuracy and rigidity of the sleeve, the effective stock of lubricant and the loading capacity of the oil film, which are in fact difficult to identify through disassembly, but these implied performance indicators are critical to the life, and only some rough analysis can be made from the structure, such as whether the axial load response of the sleeve bearing is present and effective, the existence of sealing structure, the length of the sleeve, etc.

                Even for double ball bearings, the axial support length of the two bearings (which will significantly control the impact of rotor oscillation in operation), preload pressure, bearing housing and arbor and ball bearing inner and outer ring fit accuracy, motor drive and specific operating load and operating conditions will greatly affect the life and failure rate, the wrong design of double ball bearing fans will induce early failure and thus lead to a shorter life than the sleeve This has happened in the current products.

                In addition to this, the drive scheme and electrical reliability of the fan’s brushless motor will also have a significant impact on life, as will the mounting of the Hall sensor and the overall current efficiency of the motor. (For example, phanteks T30 has a more advanced FOC three-phase sensorless motor drive compared to competing products)

                I have disassembled many cooling fans and if you are interested I can share photos and some simple information via email when I have some free time.
                I keep hoping that these will one day help someone who needs it.

                1. Of course, even a fan with a more delicate bearing can have a longer life, as long as it is better able to prevent lubricant leakage or hardening (e.g. by dust particles entering and mixing with it). A detailed analysis of a disassembled fan could shed more light on these things too. Anyway, it’s not something we want to get into tomorrow. Naturally, like everything, it requires proper preparation to make the outputs relevant.

                  If you would be willing to send us your analyses of disassembled fans by email, preferably in the form of an article that we would republish, we would be honored. When you have time, you can email me at and we’ll work it out somehow. The insights from such an examination will certainly help a lot of people. 🙂

  2. as expected, the design works well, but the finetuning and material engineering made by Noctua proved to be unbeatable once again, especially when you are aiming at total silence, below values presented here, as the lower sound pressure goes the bigger lead A12x25 has

    1. Yes, the lower the noise level, the greater the contribution of non-aerodynamic sounds. You can see this well in the “33 dBA, no obstacle” spectrograph for example, where the GT DC1225 is, between 1–2 kHz (motor and bearings), significantly noisier than the Noctua NF-A12x25.

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