Noctua NF-A12x25 PWM in detail
All the glory and respect of the Noctua NF-A12x25 “sterrox” fan is well deserved. We waited a long time to release its tests, mainly because it was necessary to analyze more seemingly similar designs first. This is necessary to understand why Noctua’s most popular fan among standard thickness models has no competition. We can responsibly say that even though we have only tested a fraction of all the fans.
We know which fan’s results you’ve missed (and perhaps missed the most) in tests so far. Anyway, if we had released the Noctua NF-A12x25 tests earlier, the ranking wouldn’t be as clear as it needs to be. To get a good understanding of why this fan is really the pinnacle in terms of aerodynamics, it’s important to understand the shortcomings of other models. That’s mainly why in the other four tests we focused on fans whose blades were similar in shape, but still with often significantly different results. We’ll go through all of that during this analysis and explain where Noctua had to go the extra mile to make the NF-A12x25 shoot to the top ranks of aerodynamic efficiency.
Because of its undeniable visual similarity, the Noctua NF-A12x25 fan immediately earned the “Gentle Typhoon copy” label right after its introduction. In reality, however, Noctua only took inspiration from the shape (much like Scythe, which once saw it elsewhere and applied it to the Gentle Typhoon), which would be rather silly to ignore. It would be similarly foolish to someone trying to forcefully come up with a “new” wheel that had a geometry other than circular. So yes, Noctua has acknowledged that the basic shape of the Gentle Typhoon is more efficient than designs with less curved leading edges, and there’s no point in denying that. At the same time, it’s nothing that can’t be improved upon quite significantly.
Akasa has also jumped on the “à GT” fan bandwagon with the Alucia SC12. However, as you already know, that is not one of the most efficient fans. This is because a very flexible material is used to make the rotor, which significantly reduces static pressure. The airflow in a non-restrictive environment is excellent with respect to noise level, but its losses due to obstacles are more significant than in similar fans with more rigid blades (and the efficiency, the ratio of airflow to noise level produced, is also significantly worse). And why is a design with more aggressively curved blades actually more efficient than designs with less curvature on the leading edges? To direct the air currents. The greater the curvature of the blades, the smaller the flow angle. From a certain point (extreme curvature) onwards, this can reduce the efficiency of the flow just as much as it reduces it when the active flow angle is too large. Aside from the unwanted turbulence created at the edges of the frame, for the same airflow, higher friction of the currents against the stator frame increases noise (and reduces efficiency).
With a rotor design like Noctua’s, there is not such a high concentration of air currents in these locations, friction is lower (and with that comes lower noise), and maximizing axial airflow greatly increases efficiency. Therefore, we can confidently rule out that a structurally identical fan (i.e. also made of identical materials) would achieve the same air with, say, a traditional rotor shape (with small curved leading edges) at a lower noise level. This would only be possible, for a number of reasons, if a rotor with a more aerodynamically efficient shape was made of a less rigid material (and thus more subject to unwanted deformation during rotation). The basis of the NF-A12x25’s success is therefore “sterrox” with extremely high compressive as well as tensile strength (unlike the Corsair AF120), and thermal expansivity is also lower than cheaper materials.
But what actually is this “sterrox”? LCP (Liquid Crystal Polymers) with something secret mixed in, which in sum refers to Noctua’s patented sterrox. But even “pure” LCP already achieves very high strength. The MSI MEG Silent Gale P12 is also made of it, and usually in the top 3 fans tested so far, it holds its own even through obstacles. It lags behinds the NF-A12x25 mainly due to less emphasis on aerodynamic details, which Noctua has prided itself on since its inception. Before we get to them (and their contribution), looking at the rotor here offers one comparison to the BeQuiet! Silent Wings (Pro) 4.
Note that the NF-A12x25 has significantly larger gaps between the blades. Naturally, these reduce static pressure, but that doesn’t mean that a fan with smaller gaps and more total blade area (which the Silent Wings 4 also has) has to achieve higher static pressure. Again, among other design details that affect the overall static pressure, the material used matters. BeQuiet! uses PBT, which although reinforced with glass fibers, is still more flexible on the Silent Wings (Pro) 4 with its relatively small thickness (especially in the weakest spots between the grooves) than LCP.. That’s what degrades the performance of the new BeQuiet! fans the most and it also causes undulations, the occurrence of more unpleasant frequency spikes in the sound and also mechanical vibrations, which transfer in higher intensity from the blades to the frame (and then to the case and so on).
Noctua eliminates these undesirable phenomena on the NF-A12x25 by using extremely strong sterrox, which, moreover, has not been skimped on. The blades are also really thick. Thanks to this, Noctua was able to reduce the gap between the tips of the blades and the frame to some 0.5 mm. In the vast majority of other fans, this gap is two to four times larger. This is naturally due to, among other things (around precision manufacturing with low tolerances), blade instability on the run. And while this is a remarkable static pressure-increasing detail, it should be remembered that of the total cross-sectional area, this air-leakage gap is a relatively small fraction. Therefore, this feature may need to be given more weight than it really has.
We expect that as part of the next generation of fan improvements, Noctua will focus more on reducing the gaps between the blades (so that the leading edges of the blades are closer to the trailing edges of the previous blades). Finally, the space between the blade tips and the frame can’t be improved much aerodynamically anymore. The increasingly popular framing (for example, as with the Cooler Master MasterFan SF120M) is suitable at most as a compromise for cheap fans that have to skimp on lower-strength materials.
It suppresses air leaks around the rotor much more elegantly. In addition to what we already mentioned (the rotor more pressed against the frame), there’s also the unconventional finish on the inner walls of the frame that Noctua introduced with the NF-F12 fan. The idea is that the surface of the frame is “roughened” by recessed triangle-shaped formations (Inner Surface Microstructures), these form a microturbulent layer which, in addition to the overall higher resistance (and thus the desired braking of the returning air by the back pressure), suppresses the break-off of air currents from the blade tips. This does not happen on smooth walls and therefore the static pressure and the volume of air flowing over the obstacle (whether it is a dust filter, a grille or a radiator) decreases. Compared to Noctua’s other fans, the NF-A12x25 ISMs have a smaller depth, which is directly related to the thinner gap between the blade tips and the frame. For the desired aerodynamic effect (eliminating airflow separation from the blade tips), while keeping noise as low as possible, less aggressive ISM dents are suitable, says Lars Strömbäck, the architect of this fan.
But Noctua has even more aerodynamic details to improve efficiency on the NF-A12x25 (PWM). One of them is the channels on the entry side of the exhaust sides of the blades, which are mainly to suppress unwanted microturbulence and thus accelerate the airflow to increase the “suction” capacity. They also partially prevent the air currents from sliding down the long side of the blades, up to their tips (this also reduces the efficiency of fans). The third important and within Noctua fans (but also in general) an exclusive feature are some kind of steps (Stepped Inlet Design) on the intake side of the frame. These are supposed to break up the sound of the circulating air with a view to reducing frequencies that should be more pronounced on normal/smooth frames, more unpleasant for the user.
And one more thing improves the aerodynamic properties of the NF-A12x25. This time, however, it is no longer a solid part of the design, but a silicone gasket that can replace the pre-installed anti-vibration pads in the corners. These are also included within this gasket, but unlike them, this gasket also fills the gaps that occur between the separate anti-vibration corners. This space naturally allows some air to escape and in turn reduces the static pressure, albeit it is not a dramatic difference. While without the gasket (only with anti-vibration pads in the corners), in a non-restrictive environment, we measured a maximum static pressure 2 % lower (2.29 mm H2O) than is specified (2.34 mm H2O), it is 2 % higher with the gasket (2.39 mm H2O). Of course, these ratios may also vary in practice depending on the mounting pressure.
To maintain the highest possible accuracy and philosophy of testing fans with pre-installed accessories (and not the best configuration for each of the measurement aspects, so as not to confuse matters), all measurements were taken with standard corners. Sooner or later, we’ll go through more situations with and without the gasket and I’ll also observe the effect of downforce with varying degrees of compression (and narrowing of air gaps) of the silicone material. But there will be a separate test for that. Now we expand on this topic mainly to give you an idea that the effect of this seal on static pressure and airflow is quite small, much smaller than the various corners on the BeQuiet! Silent Wings (Pro) 4 fans. And also because the coefficient of parameter truthfullness can have be of slightly positive or negative nature just depending on whether this gasket is used or you stay with the basic setup (with pre-installed pads).
Noctua talks about the sealing gasket in the context of liquid cooler radiators, but it also makes sense when mounting fans in system positions, although it will have very little effect on cooling performance. The biggest difference in performance with and without the gasket is at maximum power (about 3.8 %), at lower speeds it is always less, until the difference gradually approaches zero. We will certainly return to this topic in the form of more detailed measurements, probably as part of the enrichment of the NF-A12x25 chromax. black tests, whose results should match the brown-and-beige variants better, as is the case between the white and black Corsair AF120 fan variants.
We still haven’t quite covered the basics here yet though – the Noctua NF-A12x25 is a 120mm format fan with a standard profile thickness of 25 mm. The variant being measured in this test is “PWM“. In addition to it, Noctua also offers the “FLX” variant (speed also up to 2000 rpm, but only DC control), two slower 1200 rpm variants: “ULN” (with DC control) and”LS-PWM” and two with a lower nominal voltage of 5 V (again, one three-pin for linear control, and the other four-pin, with control by changing the width of the voltage pulses) capping officially at 1900 rpm.
Also worth mentioning are the above-standard plentiful accessories. Not many other companies give so many different things like Noctua for fans even in this price range. Specifically, it is a Y splitter (for connecting two fans to one connector), a 30 cm extension cable (with it you get to the final length of half a meter) a NA-RC14 deceleration adapter, rubber spikes for mounting in a case (as an alternative to self-tapping screws, which are also included in the package), and the aforementioned gasket.
* 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.
- Noctua NF-A12x25 PWM in detail
- The basis of the methodology, the wind tunnel
- Mounting and vibration measurement
- Initial warm-up and speed recording
- Base 6 equal noise levels…
- ... and sound color (frequency characteristic)
- Static pressure measurement…
- … and airflow
- Everything changes with obstacles
- How we measure power draw and motor power
- Measuring the intensity (and power draw) of lighting
- Results: Speed
- Results: Airlow w/o obstacles
- Results: Airflow through a nylon filter
- Results: Airflow through a plastic filter
- Results: Airflow through a hexagonal grille
- Results: Airflow through a thinner radiator
- Results: Airflow through a thicker radiator
- Results: Static pressure w/o obstacles
- Results: Static pressure through a nylon filter
- Results: Static pressure through a plastic filter
- Results: Static pressure through a hexagonal grille
- Results: Static pressure through a thinner radiator
- Results: Static pressure through a thicker radiator
- Results: Static pressure, efficiency by orientation
- Reality vs. specifications
- Results: Frequency response of sound w/o obstacles
- Results: Frequency response of sound with a dust filter
- Results: Frequency response of sound with a hexagonal grille
- Results: Frequency response of sound with a radiator
- Results: Vibration, in total (3D vector length)
- Results: Vibration, X-axis
- Results: Vibration, Y-axis
- Results: Vibration, Z-axis
- Results: Power draw (and motor power)
- Results: Cooling performance per watt, airflow
- Results: Cooling performance per watt, static pressure
- Airflow per euro
- Static pressure per euro
- Results: Lighting – LED luminance and power draw
- Results: LED to motor power draw ratio