I believe there are programs that can do that, for free?
But I do have to admit, fan controllers are so fucking hot, but I just want to cut corners WHEREEVER I can, and I don't think liquid cooling is feasable(sp).
Nope, there are programs that can MONITOR them, but I haven't heard of any program that can actually lower the voltages delivered to your fans by software.
Speedfan (I use it to monitor my CPU/GPU ect. temp) has options to do it, but strangely I just went to verify it, and it freezes when I get there... my computer never freezes.
I'm fairly sure you can't through software, but I could've sworn I saw it.