thx1138v2 :
If you got the 3 pin version then no, they can't be speed controlled. If you got the 4 pin version then they can be speed controlled by either the mobo or a separate controller as the previous post says. Whether or not they will actually run slower depends on the heat in your system and that depends in a large part on the airflow through your enclosure which moves that heat to the outside of the enclosure. Adding fans to an enclosue with poor air flow won't really help anything.
I don't know what limitations you have on your box, but I have been using speed control on 3 pin fans for ages.....Since Z77 been using it via MoBo utility. It's called variable voltage control and I am running 4 separate channels, all using 3 pin fans.
a) Water Pump Curve
CPU_1 (PWM) MoBo Header => Pump No. 1
CPU_2 (PWM) MoBo Header => Pump No. 2
b) Case Fans Curve
CHA_1 (DC) MoBo Header => Fan PCB_1 => (6) Fans
c) Top Radiator
CHA_2 (DC) MoBo Header => Fan PCB_2 => (6) Push / Pull Fans on XT45-420
d) Bottom Radiator
CHA_3 (DC) MoBo Header => Fan PCB_3 => (4) Push / Pull Fans on UT60-420
All 15 fans are 3 pin Phanteks SP140s
The Fan PCBs are basically the equivalent of a plain ole cable splittter although if run off a PWM header you can add up to 11 fans and use an auxilliary voltage supply from your PSU to supply more voltage than is safe to pull off a MoBo Header.
Again, the BIOS has more limited control but you can also use 3 position switched to control fan speeds (5, 7 and 12) or a rheostat
SergeantPepper :
I'm not out of fan headers but I couldn't find any place to plug them on motherboard, is that something possible?
Any gaming, enthusiast or workstation Motherboard will provide Fan Headers .... I can remember seeing less than 4 in ages. Z97 Boards typically have 2 PWM CPU Headers and t or more CHA PWM headers are not uncommon. Z87 typically had 2 PWM CPU Headers and 3 - 6 or more CHA DC voltage headers
Here's how Asus does it w/ FanXpert ..... id ya don't load AISuite, more limited control is available thru the BIOS.
https://www.youtube.com/watch?v=4i-aTUMuIB0
What mother board do you have ? The MoBo Manual should have a pic with all fan headers labeled.
For example:
http://www.newegg.com/Product/Product.aspx?Item=N82E16813132038
Hit Specs tab
1 x CPU Fan connector(s)
1 x CPU OPT Fan connector(s)
3 x Chassis Fan connector(s)
3 x Optional Fan connector(s)
1st two will control PWM (4 pin) or DC (3 pin) fans
Next 3 control DC (3 pin) fans
See pic here on page 23 of the PDF (1-7 of manual)
Also page 61 (1-45)
http://dlcdnet.asus.com/pub/ASUS/mb/LGA1150/MAXIMUS-VI-FORMULA/E8336_Maximus_VI_Formula.pdf
Fan control is described on page 132 (3-42)
FanXpert Control is described on page 163 (4-11)
http://www.newegg.com/Product/Product.aspx?Item=N82E16813132247
1 x CPU Fan connector(s) (1 x 4 -pin)
1 x CPU OPT Fan connector(s) (1 x 4 -pin)
6 x Chassis Fan connector(s) (6 x 4 -pin)
All 8 will control PWM or DC Fans