Noise measurements cannot be taken during load testing because the electronic loads and other equipment generate significant background noise. To overcome this, a non-intrusive laser tachometer is used to record the PSU fan’s RPM during operation. For acoustic measurements, the PSU is then tested separately, with the fan powered by a custom-built fanless adjustable DC PSU. Noise levels are measured across the fan’s RPM range using an Extech HD600 sound level meter, and results are cross-referenced with the tachometer data.
The testing environment has a background noise floor of ~30.4 dB(A), with equipment noise becoming noticeable above 33.5 dB(A). This setup allows accurate measurement of fan noise but does not capture coil whine, as the PSU is not powered during acoustic testing. However, coil whine is noted subjectively during live load tests.
