Stefan Mileschin

"The fans I compared to the Pure & Silent Wings 2 are be quiet!'s direct competitors. The Noctua and Phanteks fans in the comparison are all meant to be very quiet at max RPM's and they are for the most part. The be quiet! fans do not out perform them in sheer power, but they do beat them where it counts: Noise to air ratio. The Silent Wings 2 have the highest airflow to noise ratio of any fan I have personally seen or used. They are more than enough to keep a CPU cool under decent overclocked settings while adding nothing to the accumulated noise. The competitors are noticeable when there are no other noise producing components in a system. In the event that you don't want noise unless you are gaming or otherwise noise occupied, there are PWM versions of the Silent and the Shadow fans allowing silence to occupy office work for those of more sensitive hearing and keeping everything cool when stressing the computer with gaming."

http://www.overclockersclub.com/reviews/be_quiet_140/