Hi quest_for_silence. I don't have a clue what it means. I just read it at the bottom of the following link.http://www.frostytech.com/articleview.c ... 554&page=5
They also state - "The 120mm PWM fan on the Scythe Rasetsu heatsink spins at 1800RPM by default, creating a moderate 59.5dBA noise. At a reduced fan speed of 800RPM, the Rasetsu heatsink hums along at a whisper quiet 38.2 dBA. The fan has a dedicated manual fan controller mounted to a PCI bracket as is common with many Scythe heatsinks, it cannot be removed from the fan."http://www.frostytech.com/articleview.c ... 554&page=3
Hope that helps.
Yes, a tad: maybe I'll be wrong, but I see that you are brand new as a silencer...
...fans are fans, a case fan can be a cpu fan and viceversa: the only thing that matter is the fan header, you need a 3 pin (voltage controlled) or 4 pin (PWM) header to run quietly a fan. Anyway, avoid closed corners fans for a cpu heatsink or you might run into some troubles.
There are some really quiet fan (at any speed), but usually they are useless or designed for very special applications (I think to some sub-600rpm fans).
A PWM fan is a variable speed fan by design, so it doesn't have actually a "default speed", FrostyTech is referring to the higher maximum speed but there is no technical reason to assume that one as the "default speed" (and why not the lower maximum speed? Moreover their dB figures are totally meaningless).
The rules of thumb are: use a fluid bearing fan for horizontal or vertical mountings, a sleeve bearing for vertical mounting only; then, it's more important how you use the fans, than how slow they spin at their theoretical max speed.
This is why some motherboards (or rheobus) are preferable over all the others: currently ASUS and MSI have, in my opinion, the best headers to drive a fan. Using a software controller (along with the proper BIOS settings) may improve the overall situation.
Just to give you some reference, a 120-140mm fan can be quiet up to 600-800rpm speed, moderately quiet up to 1000-1200rpm speed, moderately loud up to 1600-1800rpm, loud or unbearable loud above those speeds. Smaller fans can run quicker quietly, while larger ones need to be slowed down more to be on par. I use a CM Hyper 212+ with an oc'ed X3 740 (unlocked 4 cores @ 4.2GHz) and it cools this cpu at full load with a pair of 120mm Enermax Cluster (PWM) running under 700rpm (ambient under 28°C).
Summarizing those Scythe Slipstream PWM are very quiet fans in their lower speed range and most of times running them at full speed is virtually useless even with heavily oc'ed CPUs.