When testing in a power supply laboratory it is difficult to take fan noise readings as the noise from the Sunmoon test equipment and air conditioning corrupts everything. The next best thing in our circumstances was reading off the fan speed with a tachometer to get an idea for the noise. The ambient temperature during testing held constant at 22 degrees, with 1 degree of variation. Each power supply had a consistent time period of 5 minutes to stabilise between each load scenario.
In my experience the following general relationships apply between noise levels and fan speeds, though it can vary greatly between the type of fan used.
- Below 800 RPM – Inaudible/Silent
- 800 to 1000 RPM – Barely audible
- 1000 – 1200 RPM – Audible but still quiet
- 1200 – 1400 RPM – Moderately noisy
- 1400 – 1800 RPM – Noisy
- 1800 RPM or higher – Intolerable
The above fan guideline is mainly for the usual 120,135 and 140mm fans equipped on power supplies. For 80mm fans it is very different. At 1300 RPM an 80mm fan is near inaudible, after about 2000RPM it does become noisy and nearing 3000 RPM it was very noisy. Overall the be quiet! SFX power 2 is quiet for 0-60% operation and after that the noise kicks up. To be fair this is a limitation of the form factor, it is difficult to cool 300 watts of DC power conversion and regulation in such a small space.