Excerpt: Today we're going to take a look at two Noctua case fans that look identical but are designed slightly different for different computer operating requirements. The first fan we want to test is the Noctua NF-S12B ULN . This fan runs at two different speeds; 700 RPM or 500 RPM.
Pros: Practically silent operation, cools effectively at the low speeds.
Cons: Pricier than other 120mm fans. Does not cool as effectively as other higher speed 120 mm fans and it would be nicer to have a built in resistor in the fan with a switch that can be accessed from the back of the PC instead of having to switch adapters every time you want to change the speed.