fan header slowing down fan ?

[Dicehunter]

Im just wondering if plugging your fan in to a a mobo header reduces the fan speed if compared to plugging it in to your psu, i ask bcos the exhaust fan is only 1500rpm according to asus probe, where it says on the box it came in that it does 2500rpm

 

[jak731]

it will depend on your MB, some/most regulate fan speed depending on a varible such at tempeture

 

[Mick-1965]

Have a look in the bios, see if you have Q-Fan enabled.
As said above the motherboard will slow the fan down to reduce the noise, until a defined temperature is reached then it`ll start to spin up the fan to reduce the temp.