What the...have I just done ? Please explain...

Hello to you lovely sound profis - in my recent attempts in pursuing a great ( or correct as much as it can be ) sound I again started to play with speaker connection vs speaker cable. As I really think this is the gist of my system set up - and I think I was actually correct - but why the result is so good , no clue. Ok so to sum up. I have a speaker cable "Atlas Hyper 2.0" which I have deemed really good and used it in many set ups - after so many changes I came to the point that actually the sound problem lies within speaker cable impendance vs speaker terminal impendance (?) And now something silly that made this question to you:

A few days ago I cut a small 5 cm piece of sticking tape and wrapped it around tight on of the "+" banana jack on the cable ( upper part of the banana jack other 3 jacks are untouched ) then I inserted this jack into the banana terminal in speakers ( they are monitor speakers with biwirable links - all posts are gold plated ) - The sound has been dramatically changed for the better - I mean better imaging and treble response - you can trust me as I am an analytical listener being in Hi Fi many years - what the hell have I just done from the scientific point of view ? If that helped should I replace the speakers posts with plastic covers or choose a speaker cable with increased (?) resistance - or thinner / dicker cable ? Please explain why this trick has improved the sound so much ?

P.S. Thank you in advance , I know this is silly a bit but that really works... :)
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This is why I only got a B in Electromagnetic Waves undergrad.
@roberjerman - Yes banana plugs, not jacks , sorry.

@others - Maybe we should leave this topic - I think we won't come to a right conclusion on this one. It's not just that I am a bored musician and came up with something insane - it's simply something with Cable specifications I think. I have no clue why changing or isolating anything an the back of the terminals changes SQ - I think it is unsolvable in this case. At the beginning I thought that the speakers have very instable impedance shifts but I got no clue why isolating ends of the cable improves that. Thank you anyway. 

"In the stereo application with cinch plugs, new problems arise with the spatial separation of the ground leads (L / R) of the 2 cables, which do not exist with the 5-pin DIN connector with a ground pin and common screen for both channels. If the cables are apart, the ground lines form a loop, into which foreign alternating magnetic fields, e.g., hum, or causing high frequency interference. "
Knukonceptz also offers fantastic banana plugs that are the only ones i could find to accept my 8 guage cable. Excellent contact.