If you compare the absolute values with those of the reference, then you get a very pleasing picture. No matter whether normal case fan or as high speed version – the fans always act quieter than the reference. This already hints at the surprise I had foreshadowed for the summary. But let’s look at the numbers first:
Sound comparison (recording) at 100% speed
As just mentioned, the subjective feeling is characterized by a more dominant noise of the motor and bearing, while the impeller can act almost silently. This puts the slightly better dBA values into perspective and shows that numbers alone are not everything. Nevertheless, this is all whining at the highest level.
be quiet! 120 mm standard
be quiet! 120 mm High Speed
Noctua NF-A12 PWM
As a cautionary example of what’s really loud at around 1800rpm, I’d still have a cheap 120mm case fan from a PC table labelled on a rather high priced Taiwanese case supplier that could have easily been used to run octocopters through:
Sound comparison (recording) at 1000 rpm
The sound is also very different here, even if the performance is not so far apart in the sum of the noise emission.
be quiet! 120 mm standard
be quiet! 120 mm High Speed
Noctua NF-A12 PWM
Total speed range (500 to 2200 rpm)
Before I will explain the frequency analysis of the recorded spectrum to you, there is already the dreaded “station search”, where we will play through the fan operation from the lowest to the highest speed. And please don’t be alarmed, we’ve amplified the whole thing a bit so you can hear it better. So don’t set your listening level too high, though – it’s not particularly extreme this time. The Arctic P14 was a completely different caliber…
be quiet! 120 mm standard
be quiet! 120 mm High Speed
If the speakers have survived the whole thing up to this point, let’s now go into more detail.
Frequency spectrum in the housing
Let’s look at the frequency analyses of all measurements and all three speeds tested. The graphs speak for themselves, as you can also see the lower frequency peak of engine and bearing noise very clearly with increasing RPMs:
be quiet! 120 mm standard
be quiet! 120 mm High Speed
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