The cable for the sub is just a coaxial cable with no ends, so I need to stick an RCA end on, which I've never done. I tried it, but I get some serious hum when I power on the sub, ...

Some of the most common cables you'll come across are red, yellow, and white. Sometimes, these cables come bundled together; ...

Most TVs will output audio via analog out either over RCA outputs or a headphone style jack where you can connect a 3.5mm to RCA adapter cable.

Fig. 2: A male-to-male RCA phono cable with yellow plastic and a male-to-male 3.5 mm black headphone cable. Not having a cable with a male-to-male RCA phono on each end and male-to-male 3.5 mm ...