Noctua NH-U9 Heatsink
 

Noctua’s first go at heatsink design is very promising and the results were very pleasing considering the noise level was kept at 22dB. And this could be lower if a 92mm fan was used instead like the Akasa 92mm Ultra Quiet (1400RPM, 29CFM, 18dB). Obviously increased performance would also be noted with a higher CFM fan like the Akasa.

22db..

What can I say? Perhaps, dBA would have been even lower.

they're relying on the fan's specs; no measuring was done.