Math is your friend.
9.5 feet of 14awg solid core, skin effect at 20khz adds about 0.01 ohm of added resistance. However the wire was stranded so this will be quite a bit less.
20khz zip cord speaker wire 14 awg, 9.5 feet, inductance would add 0.3 - 1 ohm AC resistance at 20khz.
For the 3rd time it's not skin effect it's inductance.
FYI skin effect is not impacted by magnitude of current until exceptionally high currents.
9.5 feet of 14awg solid core, skin effect at 20khz adds about 0.01 ohm of added resistance. However the wire was stranded so this will be quite a bit less.
20khz zip cord speaker wire 14 awg, 9.5 feet, inductance would add 0.3 - 1 ohm AC resistance at 20khz.
For the 3rd time it's not skin effect it's inductance.
FYI skin effect is not impacted by magnitude of current until exceptionally high currents.