Fans, really quiet fans

I tend to use the cheap 80mm brushless fans I can find and use loads of them in series with a few power mosfets, thermistors and 10k pots. The idea is to thermaly control the fans speed so they rarely spin at there fastest and are thus quiet...

The pot is used to select the temperature wanted, which I normally calibrate uses warm water etc. The mosfet controls the juice that each fan gets. The thermistor obviously varies its resistance with temperature (resistance reduces as temperature increases). This allows more current to flow to mosfet which in turn increases the fans revs. When they are driving one or two fans heatsinking is not needed.

Ive found that this setup gives the best thermal properies for my needs, whilst being cheap and easy to make + very quiet.

Oh, and controlling fans in this fashion is probally quite inefficient. The excess voltage is turned into heat. But when you consider the power drawn by a fan the heat produced by the mosfet in minimal. Ive attempted to use pulse width modulation, but I don't know enough in that area. Also, fans tend to buzz when spinning at low revs under PWM. (Caps needed??)

Finally rev monitoring software will not work...

Here's a place to start: http://www.silentpcreview.com/article63-page2.html

I usually read through their stuff when I'm looking for quiet component recommendations.

Also, keep in mind that while some fans are definitely quieter than others, most of the time quieter fans are quieter because they are simply moving less air.

The G4 I have in a G5 case is very very quiet. The exhaust fans are Panaflo (best out there) 92mm fans, both on speed controllers, and the CPU 70mm fan is allso on a speed controller. All three are set way down in speed, it cools very well, and I can sleep in the same room with it.

In some cases the worst noise, that jet engine whine, mostly comes from the hard drives. YMMV. In my old 7300 I never heard the fan unless the hard drives went to sleep. In fact I was never able to hear myself think unless the hard drives went to sleep. I don't have anything more modern than a Sawtooth and a Cube, but in every PowerMac I've owned the fan noise is secondary to the hard drive. That is, until I hack it

I think panaflow fans are the best as tested by my ears. If it's still too loud, use a 1W diode in series to lower the voltage a bit. Either that or a rheostat.