While PWM fan controllers are very common in today's PC industry and available on most mainboards, there is often only one or two such PWM headers reserved for the CPU and or the chipset fans. One way this excellent noise reduction idea can be extended to the numerous case fans inside a typical PC is by utilising this PWM power splitter cable, also know as a Y splitter cable.
The PWM signal input from the mainboard is used to control a series of connected PWM fans for optimal performance in noise and cooling. Connect two PWM fans to your mainboard's CPU socket by using this cable. Use multiple Y cables to provide as much extra cooling as desired, if your motherboard supports this function.
The cable is sleeved (black) and approximately 26cm in length, this includes the connectors, 1 female to 2 male connectors, 1 of which is 4 pins (which has the fan speed sensor wire), the other is a 3 pin connector. The reason for the sensor wire not being used on this connector is because if both fans were sending back information to the motherboard, it would not be able to understand that information as both lots of information would be coming back through a single connector.
What happens is the fan with all 4 wires (Master as shown in the photographs above) tells the motherboard the information, and then the motherboard controls the speed of both fans.