Its almost impossible to use dbA ratings on products because most of them either use non-standardised measuring methods or simply lie.
The only way to find out about noise is to read a review from
Silent PC Review.
They give you a noise sample, and a calibration noise to set the volume of your speakers. They also use a standardised measurement system across all their reviews.
You can also ask here on the forums and many of us who own the product can confirm that its quiet.
Heres the wikipedia article on dbA.
It says that 10dbA @ 3m is human breathing. The Nexus 120mm silent fan known as one of the quietest fans around does 23 @ 1m and i find undervolting it slightly gets it completely silent, so i would say that anything less than 20dbA @ 1m is going to be almost silent.
If you find any products near that rating however they are probably lying, such as silent x fans which claim to be 11 and 14dba, which is so low its almost impossible to measure. Having said that, Silent X are good along with nexus for fans.
And the wikipedia article on Sone
The only things i know of that are rated in Sone is the artic cooling vga silencers. If you want to know how quiet these are, let us know which model your getting and me or someone else can tell if its near silent.
Best air cooling cpu cooler is the sythe ninja. With a 120mm nexus fan its also the quietest.
