"I can remember when the first home-brew fan speed 'rheobus' was introduced on an enthusiasts website a few years back. Since then, a lot has changed in the computer world, and more than a few manufacturers have started producing their own variation of fan speed controller. A fan speed rheostat (as they were originally called) is meant to bring RPM control to the users' finger tips. With the case fans connected to such a device you can decrease the speed of each fan independently for optimal airflow vs. noise."

This review can be found at Frosty Tech