first off the original sub enclosure is not an enclosure it is a beauty board mounted to the door, the door would be the enclosure, and since it is quite larger than the required airspace of those subs with no divider between each sub it is considered a free air application (kind of like mounting a sub in the rear deck of a car and using the trunk as the box)

second off the factory amp is rated at 4 ohms per channel and it is a 4 channel amp so no the 1 channel amp diagram you showed is not the correct way to wire the subs, unless you are explaining how it is wired inside the amp (which I am pretty sure that is not how it is wired).

and third off all I am saying is if you are going to put more than about $15 or $20 into simply replacing a blown speaker with a very cheap stock replacement then that is fine, however (and I think alot of people will agree with me) if you want more volume, deeper bass and better sound quality you need to upgrade. More power and better sound quality will need a new amp and for the subs buy an 8,10, or a 12 (even a 15 if you want) and a proper box. I might also add that improper airspace is also a large cause of damaged speakers (over or under working them)

I too built my own competition systems in my teenage years, then I became MECP certified and have been installing for others ever since then at many custom shops and big box stores. I have built show cars for Mera shows, I have worked on custom Demo cars for Alpine, JL Audio, and Audison. I unfortunately hate doing custom work now because it is too "commercialized" and because of that it has lost its value.

I could have went into as much depth as you about wiring and impedance, the fletcher munson curve, speaker efficiency, etc. but most of the guys on here are looking for simple answers and dont know what half of that stuff means.

 

I'm not arguing with you. I gave a solution than cost 30 bucks and sounds great. Simple as that.

I also did show cars, Won World of Wheels and the Truck Nationals.