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... :)
Ok but to add now to your answer:

The speaker cable has really good and firm terminations with gold plated banana jacks. The posts on the speakers are very good installed ( Leema Acoustics monitor speakers ) no loose parts either in speakers or with cable.

Do you think that banana jacks have not complete contacts inside the posts ? These are Z plugs. But again - the sticking tape makes the connection even smaller (?)
Audiodav, it has nothing to do with the tape. It is just a bad banana plug. The only banana plugs I will use are the locking type. Regular ones lose their spring and get loose over time. You can take a little flat head screw driver and pry the contacts apart to make a better connection but I would rather put new locking banana plugs on. Parts Express carries them. In terms of speaker cables you want the lowest parallel and series impedance you can get. A very low gauge 10 or lower, tightly twisted pair of the shortest length you can use meets that requirement. Another great design if you want something fancier looking is Kimber cable which you can get in rolls and make your own cables. I use 12 TC. 
Ahhh ok. So it looks like the banana jack contact problem indeed. Right, there are some better locking bananas out there. Super , thank you and the others for your answers. Will do mijostyn and take a look at better connections...with maybe better cable.
Go to Best Buy and get speaker cable for$40 buk ,and avoid the problem
Banana PLUG - not "jack"! The jack is the part the plug goes into. Putting a piece of tape on a plug for an improvement in SQ - lay off the likker, ok?