vee,
For a while I was running Morrow Audio Elite speaker cables, and these had separate positive and negative cables. I found that if they were laying directly on laminate-over-wood flooring, the sound was impaired compared to if they were laying on carpet. I ended up elevating them about 5 inches using hot drink paper cups I bought on Amazon. The sound dramatically improved.
When positive and negative cables are separate, I think the magnetic fields cannot cancel like they nearly will in a single bundle cable, so they can interact with things like nails in the flooring and maybe even dielectrics in the flooring materials.
The hot drink cup elevators are cheap and quick to try. I ended up spray painting mine a dark brown to blend in better with the flooring.
Charlie