Performance TestingPlease refer to the dedicated test setup page here as it applies to this review as well and I did not want to go over it separately again.
Let's remind ourselves that the fan is rated for 450 (+/- 20%) to 2000 (+/- 10%) RPM. The provided sample, and this is all of one data point at each measurement thus, went from 1941 RPM at 100% PWM duty cycle all the way down to 226 RPM at 14% before turning off. Indeed, these fans will turn off at lower duty cycles as Noctua promised, provided you have a complying PWM controller, of course. The fan re-started at 18% PWM duty cycle and moved consistently back up to 100% with minimal hysteresis in the RPM vs. PWM curve. Speaking of which, it is fairly linear until the fan shuts down, which is good in terms of being able to predict the fan's behavior by simply setting a fan curve for linear responses henceforth over the long ~15%-100% duty cycle range. The fan being able to stop spinning completely also means you can have a system as quiet as ambient if there is no other source of noise, and the graph above goes to 19 dBA because that is the floor's ambient in my anechoic chamber used for testing.
Context is needed to talk more about the fan's performance and noise, so I have below comparison charts for some fans tested so far at set RPM values (or as near as they can get to those).
I have included fans in charts where the rated RPM is within 50 RPM of the chart cutoff point, which means that some fans are in specific charts only if their rated speed is over 50 RPM off from a threshold value (Corsair SP120 RGB, for example) or they simply do not slow down enough (NB-eLoop B12-4, for example). Similarly, the specific RPM values chosen reflect usage scenarios most popular with watercooling even though some fans (the Noctua NF-A12x25, for instance) go higher. The charts are to be considered for comparison within this result set only and are not to be compared with results from another test elsewhere owing to different testing conditions.
Well, Noctua took their sweet time with this, and it looks like it was all worth it in the end. Noctua has not really impressed me with their 120 mm fans when it comes to watercooling until now. The NF-A12x25 is a fantastic fan for this purpose, and I am quite pleased to see a product that has had performance and noise as metrics for R&D over RGB lighting. Indeed, we see that the NF-A12x25 is among the very quietest of the fans tested so far (which includes some of the very best fans in the market) while performing in the better half of the segment. To provide more context, it is about as quiet as the Phanteks PH-F120MP (which I used to recommend to those prioritizing noise while still maintaining decent performance) while performing as well as the CORSAIR ML120 PRO RGB (which I used to recommend as an excellently performing fan). As it stands today, and pending the cost factor which we will get into on the next page, the Noctua NF-A12x25 is my overall top recommendation for watercooling fans from a performance/noise basis.