Statically set the speed of a CPU fan
I added fans to the backs of my computer monitors to allow them to run cooler and hopefully extend their lifespan. I used computer CPU fans similar to yours that have the 4 wire connections including the PWM input. To lower the noise and be able to control the fan speed I built a simple little box that takes in 12V from a AC->DC wall type power module and then outputs that to four fan connectors on the back of the box. Internally I designed a very simple circuit that runs off 12V and uses two 555 timer chips to produce a 22KHz requency waveform and then uses a pot on the second 555 timer chip to create a PWM signal to drive the four fans. 

I'll post a picture of the schematic later so you could use the same design if you wish.