Subwoofer cables carry the low-frequency signal from a preamplifier, processor, or integrated amp's subwoofer output to the subwoofer itself. It is a line-level run like any analog interconnect, but usually a long one, so shielding and a low-capacitance design matter for keeping bass tight and free of hum over distance. A long run of the wrong cable across a room is where hum and rolled-off bass creep in.
The range pairs VIABLUE's NF-B, a single RCA cable with the brand's airpipe insulation and full-metal connectors, with REL's purpose-built LFE cables: the Commander, Commodore, and Bassline Blue. REL builds these specifically for the .1/LFE and high-level connections their subwoofers use, in lengths long enough to reach a sub placed anywhere in the room.