We proceed with the analysis of noise characteristics demonstrated by participants of our Massive Fan Shootout. Now we focus on 120x120x25 mm models.
Arctic Cooling Arctic Fan 12
Quite an interesting spectrum. Here is its main peculiarity - characteristic frequency base is distributed between three bands (125 Hz, 160 Hz, and 200 Hz). And the second much weaker harmonic "hides" at 315 Hz and 400 Hz. As a result, Arctic Fan 12 is subjectively less irritating than some other fans with pronounced low tonality. There is another interesting point — a small surge at 2 kHz. We are inclined to interpret it as "engine popping". To all appearances, its maximum intensity falls on this very band.
Arctic Cooling Arctic Fan 12L
It's quite an expectable situation — the middle and high sections of the spectrum go down, and the main harmonic of the characteristic frequency shifts to 100 Hz and 125 Hz. But there appears a weak surge at 500 Hz — that's actually the third harmonic of the characteristic frequency: it's obviously amplified here by acoustic effects at the grid on the fan case.
Cooler Master OAF-L12-E1
It's an illustrative spectrum. The low section is usual — we can see a distinct tone of the characteristic frequency at 200 Hz (higher by 8-10 dB), and the second harmonic at 400 Hz. But then the OAF-L12-E1 gives a "surprise" — a significant surge at 630 Hz, which is amplified with the third harmonic of the fundamental frequency (800 Hz) and is supplemented with its own harmonic (1.25 kHz). At the same time, this situation is not surprising — this surge is actually the result of nonoptimal disposition of stator's studs: the OAF-L12-E1 generates turbulent noise at the impeller/studding at 630 Hz (characteristic frequency of this phenomenon) and 1.25 kHz. Pay attention to a small surge at 2 kHz — it's popping of the engine.
Cooler Master SAF-S12-E1-GP
This situation is also quite expectable — a fundamental peak at 100 Hz (it's part of the spread-out characteristic frequency, which maximum is concentrated at 80 Hz), the second harmonic at 160 Hz, as well as subsequent mixed harmonics (250-315 Hz and 500-630 Hz). There is an unusual small rise in the high part of the spectrum (from 2.5 kHz to 5 kHz), which presumably has to do with configurational peculiarities of the impeller (scooped blade). Subjectively, SAF-S12-E1-GP is very quiet with an almost inaudible low-frequency component.
GlacialTech SilentBlade GT12252BDL-1
Unlike its 80x80x25 mm relative, SilentBlade GT12252BDL-1 does not show any individuality — according to its impeller configuration, there is a main harmonic of the characteristic frequency at 160 Hz and subsequent harmonics — separable (315 Hz) and spread-out (500 Hz and 630 Hz). Nevertheless, subjective noise generated by this fan is also quite uniform owing to the neat middle and high parts of the spectrum.
GlacialTech SilentBlade II GT12025-HDLA1
Quite an ergonomic spectrum. Characteristic frequency is based at 100 Hz, the second harmonic (slightly higher than its "neighbors") appears at 200 Hz, then follow neat middle and high parts of the spectrum (only a weak rise at 630 Hz and 800 Hz looks unusual, it presumably has to do with aerodynamic peculiarities of the impeller). As a result, SilentBlade II GT12025-HDLA1 generates quiet and uniform noise practically without harmonics.
Scythe Minebea 4710KL-04W-B29-V52
Despite the relatively high rotational speed (1900 rpm) and intensified impeller (9 blades), Minebea shows a neat noise picture: peak of the characteristic frequency is noticeable, but it's not that higher (315 Hz), subsequent harmonics are spread out — the second harmonic is spread out between 500 Hz and 630 Hz, the third harmonic — between 1.25 kHz and 1.6 kHz. As a result, Minebea's noise is not irritating even despite the raised middle and high sections of the spectrum, which are subjectively transformed into boomy air hissing.
Scythe S-Flex SFF21F
This situation is different: we can see a distinct tone of the characteristic frequency at 200 Hz (it's higher than the neighboring bands by 11-12 dB), then goes a spread-out but high second harmonic (400 Hz and 500 Hz), and finally the most illustrative issue — an unusually high third harmonic (800 Hz), which matches the fundamental frequency of the impeller/stator's studding and self-amplifies because of nonoptimal disposition of stator's studding. As a result, noise generated by the S-Flex SFF21F has a mixed tonality (you can hear muffled "howling" of the impeller). Subjectively, it's not ergonomic, one can even say that it's irritating.
Scythe YLT DFS122512L (it's the standard fan in Scythe coolers)
Quite a neat spectrum. We can see the characteristic frequency base at 125 Hz and spread-out harmonics: the second harmonic appears at 200 Hz and 250 Hz, the third harmonic — at 400 Hz and 500 Hz. Then follows a neat middle section and a low top of the spectrum. As a result, noise generated by the YLT DFS122512L sounds uniform, smoothed out, with soft hissing of the air predominating. Well, we can establish a fact that the standard fan of Scythe coolers is a good choice in terms of its noise characteristics.
Thermaltake Hong Sheng A1225L12S (the standard fan in Big Typhoon)
Another standard fan, which is used in Thermaltake Big Typhoon, looks less tractable — there appears a distinct fundamental peak of the characteristic frequency (160 Hz). Besides, we can note the unusually high second harmonic at 315 Hz, which is probably amplified by aerodynamic peculiarities of the impeller. It's all reflected in the noise profile — Hong Sheng A1225L12S is subjectively quiet, but its low-frequency harmonics are audible.
It's an illustrative spectrum. High-speed nonoptimized impeller makes itself felt here — we can see a clear-cut tone of the characteristic frequency (315 Hz) and spread-out harmonics against the background of a very high middle section of the spectrum (630 Hz and 1.25 kHz). There are two interesting issues here — a sub-harmonic at 160 Hz (it probably has to do with structural noises of the fan) and a noticeable surge at 2 kHz caused by acoustic effects at the impeller/stator's studding (additional noise is generated by the nonoptimal disposition of studding). As a result, the TFD-12025H12B sounds clearly irritating. Subjectively, one can make out unpleasant rumbling on the verge of "howling" accompanied by loud air hissing.
Effects of the characteristic frequency cannot be evaded even with the noise reduction leitmotif in the aerodynamic configuration of the ZM-F3 impeller — we can see a distinct fundamental tone at 200 Hz and subsequent harmonics: the second harmonic appears at 400 Hz, the third harmonic is spread out between 630 Hz and 800 Hz bands, the fourth harmonic is spread out between 1.25 kHz, 1.6 kHz, and 2 kHz. However, as harmonics are spread out and the spectrum features a neat middle section and a reduced (for 1800 rpm) top section, the resulting picture is quite acceptable — ZM-F3 generates subjectively uniform noise with low frequencies predominating.
Vitali Crinitsin (firstname.lastname@example.org)
June 8, 2007
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