^^^what she said^^^ lol, go look up ampacity of the wire...google should show you a chart of awg/distance. now, there is also connection point resistance, especially when it's just 2 bare clusters of wire strands touching. though it does not matter, since the current has to flow the full run of the circuit (power amp ground) and should be matched, power actually flows from ground to positive. just food for thought there....... about the mis-matched subs and enclosures, there is a lot, way over your head, but simple paints are that there is cancellation going on, which is typical, and a reason you just don't do it. you will actually get the one taking volume away from the 2, and visa-versa at different frequencies, and end up with over-powering in others, just to start with..... the fact that you did not get laughed out of, or picked fun at when competing tells me that there is no shop, or, likely active entheusiast in the area that has half a clue, AND THAT INCLUDES EVERYONE AT THAT WANNA-BE SHOP!.....
so, to make things short here- there is 2 things- one, your grounds (and power for that matter) are insufficient, and more importantly, the lack of grounding is forcing the amps to accept current from the head unit via rca shielding, and it WILL blow your head unit, just a matter of time. the dry connection on your board (yes actual technical term for the condition of your rca solder) is giving you a thump because the amp can no longer pass decent current. going with your high level is just a fix of one thing, but does not fix an obvious problem...... and before you go talking ish about my systems, keep in mind i've built several that use the same size speaker wire as you have for ground. systems that stop a running engine, jump the wipers of the windshield over an inch, make it nearly impossible to breathe, much less see anything, and i know that it doesn't compare to what many have done on this site, likely members that have posted in your thread included. as for aptitude for car audio, well i have been repairing and upgrading amps and subs, aside form all the builds since the 90's. yes, i have been to school for electronics, and no, i will not advertise my equipment to you... you have been given good advise, which (oddly enough) you could even see for yourself before stating your thread. take it or leave it. good luck
