I just configure the fan speed in the BIOS using the dynamic temperature ranges. Then without any software or OS intervention, the fan automatically adjusts its speed to the CPU needs. It goes full speed at power on and reset/reboot, and slows down once things are running. One mainboard maker I use (ASRock) slows the fan down gradually. The other (Tyan) slows it down quickly. Both then make speed adjustments as needed to keep the CPU temperature within the specified range.
I have not checked fan voltages on my computers. It is my understanding they use pulse width modulation to control the speed. I don't know what the chopping frequency is. But maybe that chopping is affecting the voltmeter reading.
