Most PC fans we purchase list the sound level of sort; label stating 18 dBA, 23 dBA etc. I have no idea how the ratings are obtained because I could never find out where those ratings came from. What I could find is something like this.Sound properties and their perception
to human ears is not linear; 40 dB is not twice as loud as 20 dB.
I consider the sound saturation in the test area at 37.4 dBA to be within the normal range as listed here
about 40 dBA. This also establishes the accuracy level of the sound meter used in this review to be within an acceptable range for a non-clinical environment. The weighing factor of dBA and dBC is explained here
Well, we now have some basis- (using dBA and not DB)1) A very quiet room in an ordinary household is about 30 dBA at night. Normally, a quiet room has a range of 30- 40 dBA.
2) A small office has a sound saturation of 50-55 dBA.
3) 3 dBA increase is just perceptible
4) 5 dBA increase is twice as loud.
5) 10 dBA increase is four times as loud
Simply put, a PC that generates 50 dBA will be 10 times louder (in our perception) than one generates 40 dBA. Assuming you are in a quiet room of 35 dBA, you would barely hear the PC if it generates 38 dBA.
If the basis has any truth, I like to know the reason for marketing a fan that generates less than 30 dBA. Hence, I intend to find out. Please bear in mind, most of the fans you find claim less than 40 dBA. Please note that I am only trying to find out what is the real sound level generated by these commonly used fans in an ordinary household and small office other than in a sound chamber and not their air-movement capability.
Let's find out ->