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8. NOISE and FAN CONTROL
The noise level at startup was a very low 14 dBA@1m. The quality of the sound was smooth, but up close, there was a surpring amount of low frequency growl. This aspect of the sound disappeared when the PSU was lifted off the niche in our load tester, so it's very likely that the noise is the result of some interaction between the PSU fan's noise/vibration and resonances in our test box. The included rubber gasket can probably suppress much of the vibration that might otherwise be transmitted from the PSU into the case. Why there is a gasket for the output side of the PSU (which would normally be inside the case) is not clear. Perhaps some of the Coolermaster cases allow the PSU to be mounted from within.
The spikes between 150~200 Hz correspond to the growl mentioned in the text
The growl remains at 250W load
The fan voltage did not change until the 200W mark, when SPL rose to 18 dBA@1m. The overall noise character was still smooth, mostly broadband, with a bit of growl. Beyond this load, the fan speed increased steadily, reaching 25 dBA at 300W. The 30 dBA point was breached at around 500W load, and the maximum fan voltage of 12.2V was reached at 550W load, with a relatively low 34 dBA SPL.
There was a healthy degree of hysteresis in the fan control. It kept the fan from ramping up and down audibly.
Like most quiet power supplies, the M700W keeps itself cool enough, but its fan should not be counted on to keep the PC case cool. As expected with a hogh efficiency power supply, the exhaust temperatures stayed modest at lower loads. Above ~250W, the exhaust and intake temperatures seemed a touch higher than usual. There was no misbehavior associated with overheating.
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