Signature 650 PSU: Antec's Challenge

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8. FAN, FAN CONTROLLER and NOISE

The PSU fan stabilized at around 720 RPM shortly after being powered on. The fan was just barely audible. From within a few inches, it was a bit of buzzing combined with some hiss. From farther away, it was quite soft and benign, as you'll hear in the MP3 recording. It's one of the quietest PSUs we've tested, at least at idle. In the anechoic chamber it measured around 15 dBA@1m, while in the live room it was 18~19 dBA@1m. The latter was the only measurement taken in the old live test room.

The fan speed remained constant until somewhere past 250W, where it rose slightly to 900 RPM, and our sound meter registered a tiny 1 dB rise to 16 dBA@1m. After a few minutes at 300W, fan speed jumped to 1220 RPM and became far more audible, registering 18~19 dBA@1m. It climbed to 27~28 dBA at 400W, and somewhere a little above 400W output, the noise level passed the 30 dBA@1m arbitrary demarcation line beyond we define as "too loud". As the fan speed and noise level increased, so did the overall perceived tone or frequency. At full power output, the PSU sounded like a 3" fan spinning at over 4,000 RPM. Lots of wind turbulence and a fair bit of whine. Hardly quiet.

The charts below from our SpectraPLUS audio spectrum analyzer should be self-explanatory. Note that the noise floor of the anechoic chamber is 11 dBA. The blue or green lower line is ambient level of the chamber without any noise sources.


The black line is the frequency spectrum with the Signature 650 running, up to ~250W.


The blue line is the frequency spectrum with the Signature 650 at 250~300W.


The blue line is the frequency spectrum with the Signature 650 at 400W.
Note: The scale of this graph has been shifted up 5 dB to fit the curve.

The sharp spikes at 1 kHz and 2 kHz are audible; they are part of the somewhat complex tonal signature of the fan. The >15 kHz peak in the top curve was not audible (to me, anyway). It may be real, but it's at too high a frequency and too low a level to be significant. The other curves don't display this peak.

COMPARISONS

How does this compare with the quietest PSUs that SPCR has reviewed? It's quite close to the best, the Enermax Modu82+ 625W, at least until the fan starts speeding up. The difference in measured SPL at low load between the Modu82+ and the Signature 650 is less than 3 dBA@1m, and they're both so quiet that unless you have a system of truly quiet components in a really quiet room, you may not appreciate the difference. But the Signature fan ramps up at a lower load point than the Enermax Modu82+ 625W, and several other competitive PSUs. Its 80mm fan gets louder both subjectively and by measured SPL, than the 120mm fans of the competition simply because it has to spin faster to move as much air.

Here's the 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.

In the comparison table below shows the SPL versus power load data on all the PSUs tested in the anechoic chamber thus far.

Comparison: Various PSUs Noise Vs. Power Output in Anechoic Chamber
Model
90W
150W
200W
250W
300W
400W
500W
6~700W
Enermax Modu82+ 625*
13
13
14
15
16
26
36
37
Antec Signature 650
15
15
15
18
18
28
36
47
SilverStone DA700
18
18
18
18
23
32
35
41
NesteQ ECS7001
22
22
22
21
23
25
36
37
PCPC Silencer 610
20
24
24
24
24
30
40
50
*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 may be low enough to match the Signature; its measured SPL in the live test room was 20 dBA@1m, compared to the Signature's 19 dBA.

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 or better.



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