How to measure fan noise value?

The RDKcooler fan was tested in a reverberant room with a background noise of less than 15 dB. The fan to be tested is operated in free air, and a noise meter is disposed one meter away from the fan inlet. The Sound Pressure Level depends on the background factor, and the Sound Power Level is expressed by the following formula:
SPL=20logP/Pref and SWL=10logW/Wref, where P=sound pressure Pref=reference sound pressure W=noise noise energy Wref=noise noise energy.
The noise of the fan is usually plotted in the frequency band of the sound pressure level (SPL). The effect of the change in decibel (dBA) is shown by the following phenomena:
3 dBA has almost no feeling
5 dBA feels
10 dBA feels twice loud
Noise level:
0-20dBA is very weak
20-40dBA weak
40-60 dBA moderate
60-80dBA loud
80-100 dBA very loud
100-140 dBA deafening