Firstly a brief overview of my system cooling:
- two 120mm fans mounted in the side panel (holes cut of course) using bolt/nuts with a bit of foam inbetween for damping. Both bring air into the case.
- the top one is ducted directly to the CPU heatsink: Thermalright SLK900A which works a lot better than direct mounting, because of the large 'overhang' that 80 and 92mm fans give with this heatsink. Its a Duron1400 modded into an AthlonXP running at 1980mhz 1.55V
- the lower one gets some air over the graphics card to which i've attatched a bigger heatsink. The Ti4600 still gets warm and, non ducted, this fan needs to spin faster to avoid 3d artefacts than the CPU fan. (I should duct it but thats tricky)
- finally an 80mm fan mounted with the same 'foam sandwich' on the outside of the PSU is the only way out for the air..
- The HD is a 160GB 7200RPM Samsung, hanging on some rubber bands from the lowest 3.5'' slot, surrounded by 4.5cm pritex foam. I can't hear it spinning or seeking at all.
I bought 2 Papst 4412FGL fans about 2 years ago when I first entered the Silent The Damn Thing business. Being incredibly picky I didn't like them too much.
In the meantime however I tried a few more fans. The 'Noiseblocker Sx1 120mm' looks great on paper, but along with all other 'super silent' noiseblockers, they emit high frequency 'whining' at certain voltages / RPMs which is quite irritating.
I also tried a Titan 120mm fan (don't know the product number) because it seemed to run so smoothly. It does, but again when slowed down a lot, high frequency annoyance comes into play.
Lastly was a SUNON fan, that was just too high CFM. At 7v it was still about to lift my pc from the ground, and 5v it wouldn't handle. Not really worth mentioning here actually, but a lot of laughs trying it out in anticipation...
The Papst fans are totally free of high frequency sound. Bear in mind that I really use the fans at LOW speed, sub 5V with my fan controller saying 450 for the CPU fan and 540 for the lower. Sub 700RPM the aforementioned fans started to make hideous (sp) high pitched noise. The papsts just 'whirr' slightly, like the idleing diesel engine mentioned earlier. The sond level of this is very low, and the frequency well out of the 'irritating' range. When not whining high, the 80mm PSU noiseblocker fan is pretty good at around 850rpm
The point is that for really slow fans, sub 5 volt, the Papst 4412fgl are the best I heard..