There is an interaction between a speaker cable and a particular speaker. The location and depth of the dips in the frequency response depend on the speaker’s impedance and wire’s impedance. Each speaker design is different. For the wire’s impedance, thickness (gauge) of the conductor and the length of run from amp to speaker are the major concern. Counter intuitively, the higher the “gauge” of the wire, the thinner it is. So, a 24-gauge wire is half the diameter of a 12-gauge (and about one fourth the impedance). For comparison, common lamp cord, sometimes called “zip” cord, is 18 gauge.
There can be a synergy between a particular speaker and a particular speaker wire. For a while in England, there was a major discussion of how thin, single conductor, twisted pair wire sounded much “better” than the thick multi-stranded wire. Using high-end mini-monitor speakers, well controlled, volume-equalized, sighted and blind tests consistently came to that conclusion. However, it was determined that the extra resistance of the very thin wire changed the balance of the speakers in a very positive way: bass went up and treble went down. This gave all music a better foundation and non-fatiguing treble. A thick, multi-stranded wire with a resistor of the correct value now sounded the same as the thin wire. The thin wire even improved some vented systems if they were booming at the vent resonance.
Source: Does speaker wire affect the sound?
I'm gonna try 1.5mm instead of my 4mm speaker cable and hear if that makes a difference. Trying to fix a 70Hz bass hump in my room with cheaper wire. Has to work.