It is hard to conduct proper acoustics measurements on a PSU since you have to isolate it from the loaders; they are too noisy and interfere with the readings. However, moving the loaders far away from the test PSU requires long connection cables, which incur increased resistance. Power losses become significant in that case.
Thankfully, we found a way around these issues. With the help of a fully-featured hemi-anechoic chamber, we can conduct accurate sound measurements using a Class 1 Sound Analyzer.
We measure the fan's noise from one meter away. The noise measurements are conducted with a Class 1 Bruel & Kjaer 2250-L G4 Sound Analyzer, equipped with a type 4955-A low-noise and free-field microphone which can measure down to 5 dB(A). We also have a type 4189 microphone with a 16.6-140 dBA-weighted dynamic range. The sound analyzer is installed into a hemi-anechoic chamber, allowing for lower than 6 dB(A) ambient noise. A Bruel & Kjaer Type 4231 is used to calibrate the sound analyzer before every noise measurement.
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