Is a "Y" Splitter Needed to Hook Up My Subwoofer?
In order to hook up a powered subwoofer properly, an RCA "splitter" cable ("Y" cable) is not needed.
Any single, standard RCA or subwoofer cable should do just fine. However, if the sub is exhibiting a hum with the RCA/sub cable plugged into it, then maybe try using a "shielded" subwoofer cable.
Monoprice, for example, is a manufacturer of quality shielded subwoofer cables: https://www.monoprice.com/product?p_id=2684
For more information on this "humming", and how to prevent it, please see our article - Thumping/Humming Noise in Sub
One end of the subwoofer/RCA cable will be plugged into the Subwoofer Output on the back of your receiver. This output jack is sometimes labeled as SUB, SUB OUT, SUB PREOUT etc.. The other end of the cable will be plugged into the L/LFE (white) RCA jack on the back of your sub.
Any cable designed for subwoofer use should be just fine. It doesn't have to be expensive; the cheaper ones work just fine as well.
In addition, if you still use the RCA "Y" splitter cable, you have the potential to boost the sub's output signal when plugging into both the red and white RCA inputs on the back of the sub. If you choose to do this, please note that connecting both inputs in parallel will double the input voltage which equals a 6dB boost in output. However, the input impedance will then be effectively "halved" and that could potentially cause loading problems for some sources (receivers, amps etc.). Overall, it is not recommended to use a Y-splitter on any of our powered subwoofers that were manufactured in the past 10 years or so.
For more information on the best way to hook up a subwoofer, please see our article - What is the Best Way for Me to Hook Up My Subwoofer?