Because it's tested in open air with the noise meter only 150mm
away from the fan. Note the noise meter
only goes down to 30dB. So, who knows what the fan is actually adding to the baseline noise floor. Always look at the test setup in these reviews...
1 meter away with a 10dBA noise floor and attached to a testbed heatsink.
Just the difference in distance accounts for ~16dB. (hope I did my inverse square law math right
That's pretty much what I thought I was going purchase two these to try out becuase the 120mm Scythe Gentle Typhoon,and Noctua NF-S12B FLX are twice as expensive not to mention the 1200rpm S-Flex FDB was the best fan. I expect them to be around same noise level or bit higher then 800rpm,1200rpm S-Flex FDB.