I've achieved another one of those small victories on the way to a completely silent, yet powerful computer.
I've now reduced the number of fans in my case to 2. I've got a 92mm Papst running at 5v in the power supply, and a thermally controlled 120mm Panaflo exhausting out of the case.
Yeah, that's right, there is no fan on the processor. And its not some wimpy C3 either, its an AMD XP 1900+
It's staying cool through a combination of the Zalman CNPS6000CU cooler, undervolting it to 1.55v, running CPUIdle, and the new part, a duct running from the 120mm Panaflo to the heatsink.
I wedged the thermal diode from the Panaflo in between 2 of the vanes of the cooler, so that the fan now adjusts according to the temp of the heatsink. Even after stabilizing at full load the fan is running at less the 10v.
The systems temps are: Cpu 42 at idle, 55 at full load. The case temp has remainded constant at about 30, with the hard drive hovering around 40.