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8. FAN, FAN CONTROLLER and NOISE
The PSU fan stabilized at 3V shortly after being powered on. We know from testing the fan on its own that its speed is 770rpm at this voltage. The fan
was barely audible out in the open, and even in the confines of the PSU and its impedances, it was extremely quiet at 14 dBA@1m. From about 1' distance, there was a bit of audible electronic buzzing which is typical of PSUs. You can see these noises as the 13kHz and 18kHz spikes in the graphic below, but note that the level is well under 0 dBA.
The fan voltage/speed remained constant until 400W, where it jumped to 4.7V/1300rpm, and SPL went up to 24 dBA@1m. The overall noise level was still modest, and the sound quality was mostly benign, except for a touch of droning hum. At 500W output, the noise level reached 37 dBA@1m, well past the 30 dBA@1m point beyond which we consider "too loud". By this point, the noise was almost entirely wind turbulence. By 650W, the fan was at the highest speed it would reach, with 10.7V across its terminals producing an SPL of 42 dBA@1m.
This is a very steep climb in noise and fan speed from <400W output. As the fan speed and noise level increased, the perceived tone or frequency also increased a bit, but the main subjective impression was increased turbulence or broadband noise. At full power output, it was pretty loud, but not really that annoying, as there was little in the way of a piercing tonal noise.
The graphic below from our SpectraPLUS audio spectrum analyzer should be self-explanatory. Note that the noise floor of the anechoic chamber is 11 dBA. The green lower line is the ambient level of the chamber without any noise sources.
The blue-red line is the frequency spectrum with M12D-850W running, up to nearly 400W.
The frequency spectrum with the M12D-850W at 400W.
COMPARISONS
How does the M12D 850W compare with the quietest PSUs that SPCR has reviewed? It's just about equal to the best, the Enermax Modu82+ 625W. The M12D is about 1.3 dBA@1 louder at low load, but they're both so quiet that you may not appreciate the difference. Similar things were said about the Antec Signature 650, which measured 1dBA higher than the M12D and 3 dBA more than the Modu82+ 625W, but its ramp-up curve was a bit steeper, and its highest noise considerably louder, due mostly to the higher rpm of its 80mm fan.
As the power load increases, the Seasonic actually stays just a bit quieter than the Enermax, because the Modu82+ fan creeps up in speed between 200W and 300W load, while the M12D fan stays unchanged from startup till nearly 400W. Which of these two models deserves to be in the top spot? It's really too close to call.
Here's a comparative chart on the 12.74 dBA@1m idle Enermax Modu82+ 425W in the anechoic chamber with the current audio test gear.
In the above chart, the area between the black and green traces represent the Enermax PSU's acoustic contribution. From a meter away, I have to strain to hear it. The peak at ~15 kHz is audible as a low level "hiss". You may be able to hear this in an MP3 recording on the next page.
The comparison table below shows the SPL versus Power Load data on all the PSUs tested in the anechoic chamber thus far.
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Comparison: Various PSUs Noise Vs. Power Output in Anechoic Chamber
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Model
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90W
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150W
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200W
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250W
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300W
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400W
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500W
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6~700W
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Seasonic M12D 850W
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14
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14
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14
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14
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14
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24
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37
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42
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Enermax Modu82+ 625*
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13
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13
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14
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15
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16
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26
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36
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37
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Antec Signature 650
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15
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15
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15
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18
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18
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28
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36
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47
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SilverStone DA700
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18
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18
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18
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18
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23
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32
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35
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41
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NesteQ ECS7001
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22
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22
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22
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21
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23
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25
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36
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37
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PCPC Silencer 610
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20
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24
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24
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24
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24
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30
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40
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50
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The green boxes represent 30 dBA@1m or higher SPL.
*Guesstimates based on the Modu82+ 425's idle in the chamber and the Modu82+ 625's load test.
The green colored blocks are 30 dBA@1m or greater SPL readings. The PSU that stayed quiet (under 30 dBA) to the highest load is not in this table because it has not been tested in the anechoic chamber: The Zalman ZM1000, which stayed below 30 dBA to almost 600W load. It's idle noise is probably not low enough to match the M12D-850W , the Enermax, or the Signature 650; its measured SPL in the live test room was 20 dBA@1m, a dB or two higher than the others.
Caution: Please keep in mind that the data in the above table is specific to the conditions of our test setup. Change the cooling configuration, the ambient temperature and any number of other factors, and you could change the point at which the fans start speeding up, as well as the rate of the rise in speed. The baseline SPL is accurate, however, probably to within 1 dBA.
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