Noctua's NF series has now been heavily updated and the long model number in the header is simply because Noctua sells a set of NF-A14x25 G2 fans as two pieces with accessories. That's why they're called Sx2-PP, as it's a set made specifically for Push-Pull configuration. It's also a super nice and extremely informative package with a lot of extra accessories. However, we have also tested individually.
You can also get a version called LS-PWM, or Low-Speed. This lets significantly less air through, but the noise level is also only 12 dB, so good luck hearing it. There is even a round version called A14x25r G2 for air coolers. Just to emphasise how much of a geek Noctua are, their top of the line air cooling model comes in two different versions, each optimised for AMD and Intel CPUs respectively, with minimal differences in their surfaces, opening up the possibility to optimise slightly and even get a few degrees more cooling out of it versus a model that works with both.
Noctua is not a company known for churning out new versions of the same product. The G2 version of the NF-A14 fan has been a decade in the making, and it's most likely a mix of having a pretty good starting point and taking small steps at a time, all the time. I only retired some Noctua fans I had last year that were probably over 15 years old, not because they were defective, but simply because I had given up on cleaning them.
But the NF-A14x25 G2 PWM is Noctua's new 140 mm flagship model. There are a number of clever abbreviations, but they all cover real production methods and optimisations. So it's not the marketing department, but the engineers at Noctua who have the big budget. Unfortunately, the price reflects this: £70 for a single one and around £130 for a set of Sx2-PP.
It's all made with liquid crystal polymer, a fantastic plastic material that, funnily enough, also comes in a version called Kevlar, which most people are probably familiar with. The version Noctua uses is called Sterrox, which has the property that it forms a very uniform chain structure when melted. It's their own version, using fibreglass for stiffening at the molecular level, and it's characterised by high intrinsic inertia, strength, virtually no thermal expansion, and it's free of creep, a phenomenon where polymer materials subjected to sustained mechanical stress continuously deform, even at room temperature. Like I said, Noctua are geeks on a slightly different level than most. Even the hub where the blades meet has been thought out and optimised.
Then there's the use of impellers with winglets, the upward-facing fin seen on some Boeing and Airbus aircraft, which provides extra lift. But I wonder if Noctua uses them more to stop the vibrations that occur because there is a pressure difference on the fan blade, as one side sucks and one side blows. Thus, there is a difference in pressure.
So, why should you buy an Sx2-PP kit? Because we need to take a step up the geek ladder. The fact is that two fans running push-pull, meaning they throw the air in the same direction and one sucks while the other pushes the air, can create some audible interference. By having them at minimally different speeds, one 25 RPM slower, the other 25 RPM faster than the set speed, you avoid this. Adjusting 1% of the fan's maximum speed requires a lot of fine-tuning, but it's a good thing Noctua uses an etaPerf motor, one with magnetic sensors and high efficiency, combined with a strong motor system that can also compensate for the static resistance often found in a computer case. Should you be so unlucky that the room in which the machine is placed still causes ringing or noise at these frequencies, you can simply adjust the software, or go old-school by using a low-noise adaptor that is included.
One of the great things about these fans is that they are optimised to work against solid surfaces, such as on an AIO or other cooling functions, while retaining many of the acoustic improvements such as rubber cuffs and gaskets that reduce vibrations transmitted to the chassis. It even comes with a silicone membrane for mounting on water coolers for optimal damping, oh, and there's a six-year warranty. That may not mean much, as they are rated for a lifespan equivalent to over 17 years, 24 hours a day. But none of that matters if the performance doesn't match.
Noctua promises a speed of 1500 RPM, airflow of 155 m³/h/91.6 CFM and a maximum noise of 24.8 dB or 19.7 dB with the low-noise adapter. It should also be said that they consume just under 2.3 watts on full hammer.
We measured 1513 RPM at maximum speed, not that you would normally get up there, and just 2.28 watts. The noise was measured by having a frame that the fan is clamped to and connected to a PWM controller to avoid background noise from the computer. At 1500 RPM it reached 27.78 dB, also a lot more than stated. But the maximum speed was also higher. The noise didn't have to be turned down much before it dropped to 25 dB. Unfortunately, we don't have access to sensitive equipment that can measure below 20 dB, so we had to give up testing with the low-noise adapter - but we can add that it can only be heard when you bring your ear very close, and then it's still mostly just a whisper. Because even if you can measure some sound, it's relatively low frequency and impossible to hear once installed in a computer.
Pretty consistently, the temperature was 1.5-2 degrees colder, no matter what other fans we tested against from the expensive series from the big brands. Unfortunately, I don't have access to a 420 mm AIO PT, but I can't see that the result would be any different because of this. The most fun was almost firing them up at full blast and then feeling the insane cold and airflow that came through the High-Airflow enclosure used, while being completely silent.
Noctua is - still - the king of fans with this updated version.