The Phanteks’ PWM Y-Splitter cable allows you to connect two PWM fans to one PWM port for optimal performance and cooling. Only one of the two fan connectors carries the speed control signal, thus there will be no interference when using two PWM fans. And the fully sleeved cable design makes for a clean, professional look inside your computer case.
Compatible with 4-pin PMW fan connector and 3-pin fan connector
Only one of the two fans sends its tach signal (the one with full 4-pin connector) and reports its RPM, but the other one will still follow the PWM signal.
The other connector's tachometric signal pin is missing, which ensures your fan speed monitor won't bounce all over the place from getting two sense signals. This guarantees your motherboard gets an accurate RPM signal.