How do you "undervolt" the fan?
- Some motherboards have this feature
- Use 4-pin power supply plug adapter and swap the fan's ground
wire with 5V for a (12-5) 7V potential difference. Remember NOT
to use the other 4-pin end of the adapter to power anything else
(like a drive)
http://www.svcompucycle.com/3pinto4pinad.html
- Use same or similar 4-pin power supply plug adapter and swap
the fan's 12V power wire with 5V, for 5V operation of course. If
both 4-pin ends of the adapter are swapped (so correct voltages
are still maintained at correct pin-positions, adapter could then
still be used to power another device. This is a popular cheap
way to do it and Googling "7 volt fan mod" should find a bunch of
detailed descriptions.
- cut/solder/shrink-wrap a series of diodes (in series with) fan
power wire
- cut/solder/shrink-wrap a fixed or variable resistor in
series...
- Make your own variable voltage supply out of a linear
regulator like an LM317 or similar
- Make your own fixed voltage supply out of linear regulator
- Make your own PWM controller, or switching type... "make your
own" schematics aren't too hard to find for variable low-voltage
control circuits, google search them (though of course they may
take most time and $ if you don't already have misc. parts).
- Disasemble fan and substitute different fixed resistor or
replace with variable resistor in 1-2 spots on fan PCB (usually
hard to do with small, compression-fit fan hubs but easier with
large fans)
- Ready-made fan controller on the adapter, ex: Zalman
- Ready-made fan controller front bay panel, ex:
http://www.svcompucycle.com/fanandtemman.html
I'm sure there are some other ways to do it too, but one of the
above should suffice. The quick-n-dirty fan adapter is the
cheapest using std. ground shipping, and SVC (among others) also
sells panaflos.
http://www.svcompucycle.com/3pinto4pinad.html