I’ve had good luck with directional RCA cables from worlds best cables made with Canare L-4E6S, Star Quad, Audio Interconnect Cable and Amphenol ACPR Gold RCA Connectors – Directional Design. They come in different lengths and they will custom make a length for you if you contact them. Here’s a link to one: RCA – The Worlds Best Cables. Also look/search on Amazon because the selection is different than on the website.
The extra conductor eliminates any noise that RCA is prone to, they are good quality, give good sound and they don’t cost an arm and a leg!
If your sub has XLR those would be preferred and if your sub has speaker level inputs even better "depending on your equipment".