Cooler Master Aero 4

I am using the Cooler Master Aero 4 and I am trying to get the most speed out of the fan possible. I am not concerned with noise levels, and the website says it can range from 1900~3500 rpm. According to my ASUS Probe, the fan is spinning around 2300. How do I increase the speed of the fan? The knob that is on the back of my comp that connects to it is turned all the way up.

hxxp://www.coolermaster.com/index.php?LT=english&Language_s=2&url_place=product&p_serial=ISB-V73&other_title=+ISB-V73+Aero%204
MB ASUS P4P800 DELUXE SPRINGDALE RT

POWER SUPPLY ANTEC TRUE430 ATX RTL

CPU P4/2.4CGHz 800M 478P/512K HT RT

DDRAM 512MBTWINX512-3200C2 COR RT

HD 120GB|WD 72R WD1200JB 8MB-CACHE%

HD 36GB|WD 10,000 WD360GD 8MB

CDRW LITEON|52X32X52X LTR-52327S BK

SOUND BLASTER|AUDIGY 2 PCI SB0244 %

CPUFAN COOLERMASTER ISB-V73 AR4 RT

Raedon 9800 Pro 128 MB