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8. FAN, FAN CONTROLLER and NOISE
The PSU fan stabilized at around 630 RPM shortly after being powered on. The fan
was clearly audible, mostly a lower frequency, buzzy hum. It's
not the smoothest PSU noise at idle, but it's at a fairly low level. In the anechoic chamber it measured 16 dBA@1m, while in the live room it was 22 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. After 5~10 minutes at 300W, it was registering 23 dBA and sounding that as well. Surprisingly, by 400W, the SPL exceeded 30 dBA@1m, our standard demarcation point beyond which lies "too loud". In contradiction to the data in other web reviews, the fan exceeded 1600 RPM said to be the top speed at 12VDC by 500W output. It measured well over 2000 RPM at maximum load. Interestingly, the SPL at full power was substantially lower than with many other PSUs that are actually quieter through most of the range.
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 line is the response at moment of screen capture; the red line represents the peak values in the previous few seconds.
In the middle chart above, the area between the black and green traces represent the DA700s acoustic contribution. The sharp spikes at ~180 Hz and 200~300 Hz are audible; they are the tonal hum quality in the sound.
How does this compare with the quietest PSUs that SPCR has reviewed? Pretty well, but it is not in the same league as the best. This is a bit awkward to quantify or prove because all the measurements and recordings of the quietest PSUs were done with the previous generation of test gear, without the anechoic chamber. So, extra time was taken to do a quick spot check of the current reigning quiet champ, the Enermax Modu82+. The model we reviewed was a 625W, but one of those was not handy while a 425W model was. Having listened to one before, I know it sounds very similar to the 625W model. Its fan would likely ramp up at a bit lower power level than the 625W model, but that was not a primary concern. Since most systems work at idle most of the time, the acoustics at idle are far more important, and that's easier to test.
Here's the comparative data on the Enermax Modu82+ 425W in the anechoic chamber with the current audio test gear:
The SPL reading is not an error. It does say 12.74 dBA, and that's with the mic a meter away. To give you a better appreciation of just how little above the ambient this is, here's an overlay of the above curve atop the ambient curve:
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 audble as a low level "hiss". You may be able to hear this in an MP3 recording on the next page.
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