I used a pair of Amazon Basics RCA cables for subs for a long time. I only needed 10 feet and I was able to split the white & red for stereo subs.
For a long cable, this is fine.
For an incredibly nice cable, Canare makes a coax with stranded center conductor for extra flexibility and matching crimped connectors.
Premium series RCA cables hand crafted in our shop using Canare LV-61S coax and Canare RCA connectors. All components used are impedance matched for cleaner and sharper video resolution, allowing our low loss cord to offer outstanding video bandwidth performance.
www.markertek.com