Joe X

Voltage drops mean your electrical system can't handle the power the amps want, electrical upgrades (agm battery or batteries, alternator, big 3, power wiring) are available to fix those voltage drops and when that is fixed you need to setup your gains so that no clipping occurs. your electrical system upgrades need to be calculated to match the needs of your system but not significantly exceed what is needed as you may end up overspending badly.

So here is a suggestion, power: to sub(s) rated, amp subsonic filter to 28Hz, minimum port clearance 3 3/4", figure is just an assembly guide: NOTE: If building outside you need to build a cardboard dummy box to test fit in it's way inside. NOTE: Since your seats fold down you can fire forward and seal off or you could do the more common firing subs back. NOTE: Wood thickness is one inch for this design.

Seats fold down?

You need a port diameter clearance to the back wall for those ports, I would just do a slot port 30 square inches of port area instead of 3D printing some bent ports but whatever. To get the airspeed enter the power but DO NOT press enter, instead click on the plot and it will be updated. Since this software is no longer being updated that bug will stay there forever.

In a 2.2 net @35 Hz, two 4" round ports ported box (estimated size from your measurements) I get 30.1 m/s @1500W RMS using bassbox pro, for round ports up to about 35 m/s is reasonable, if it was a slot port about 25 m/s is about what you would have. Take care on how you enter numbers and other calculations.

For a 12 of that power you need like two 4" ports, usually mounted on the side of the box so that they fit without turning and do not use the baffle. To me is better going slot port with about 30 square inches of port area.

Check out these two to make your mind on what to do:

Glad to see you finally got everything sorted, I am not surprised you got into trouble with that amp though, it's a radical departure from the V1, V1.5 design, so it's a new architecture, as you know the V1.5 fixed many of the issues of the V1, it is always like that, one should never buy the first revision of a new product, also buying a D1 sub to work alone is problematic as 1 ohm power is so easy to find and inexpensive. Now you have lived through it, I guess your next upgrade will go a little smoother. Certainly hope so. Best of luck.

I would bridge both channels to get 300W each side and then use passive crossovers so you can get the tweeters powered too. That way you preserve stereo and balance and you are giving 300W to those mids which is their actual power.

If you have 4 channel outputs from your factory head unit and you want the ability to fader then use the lc5i. If you have only 2 channel outputs from your factory head unit then use the lc2i, use splitters to feed the 4 channels full range inputs on the amp, you won't be able to control fader from the head unit but you can have a fixed fader using the gains on the amp front and rear channels. The sub channel goes to the sub input of the amp in either case. So, in the end you could use either LOC just bearing in mind the above mentioned limitations of using a 2 channel LOC.

Put the secondary battery in the back close to the amps makes sense due to lesser electrical resistance of shorter power wires between the battery and the amps. But if you run multiple wire runs to the back you can also lower resistance that way so if you are able and inclined to run two batteries in the front, it is still possible to do. Also when you are running a lot of current it is recommended to avoid grounding to chassis, it is better to run ground lines directly to the front.

If you are familiar enough with audio technology and can understand amplitude vs frequency/phase plots (bode diagrams) read the Loudspeaker design cookbook 7th edition by Vance Dickason chapter eleven to understand the acoustics inside vehicles, a bit dated book maybe but enough infos to get your questions answered.

The length of the ports is dependent on the exact net internal volume of the box so you need to calculate that first. If you have external or internal dimensions of the box I might be able to do the calculations, if you want to do it yourself get something like the Torres calculator software which is free if you can find it.

You can try the following: https://fixmyspeaker.com/

Some 56 square inches of total port area, two ports half that number for each port.

Yes what you intend to do is safe, to get better results make sure you use the same sub model and the exact same box design and gain match the amps if possible.

With a single D1 sub you could connect 1 amp to each coil of the sub and gain match the amps but that is theoretical, since they are different amps those differences would likely end up causing unpredictable issues. In any case having two subs and using 1 amp to each sub would be far safer specially if the box has separate chambers. You are far better off selling the amps and getting a single amp to drive the sub or subs, a single skar 2000W amp is just a little over $200 new. Also if you can't fit two 12s maybe you could fit a single 15", much louder than a single 12" on the same power. Mixing stuff that was not meant to be mixed almost always lead to either bad performance or worse issues, my vote is just don't do it or think about doing it, do what you know it should be done and stay away from trouble.

Almost all people using those small subs want to hit the lows better, that will be because the box is improperly designed and/or those small subs are not the best for deep bass. The only way to compare two given subs is by using WinISD on both and compare plots on the box and power you intend to use, the program will show their differences, you won't find a single person than has experience with two given subs.

Probably the best 8" sub will be the Sundown X8v3, using 4 of them would require a 4000W RMS amplifier, if you do have space for a proper box for them you would be far louder.

You can delete your rear seats and do ported, no actual need for a blowthrough, or you can also get someone to do the job for you, who has measurement instrumentation, there are always options.

Post max dimensions for a box and if seats will fold down.

Car audio forums are rather empty these days. We are in a social network era it seems.

That amp likely delivers half it's rated power, just build the system and test if there are sings of stress like dropping voltage, if so then consider upgrades. For now I would do a big 3 upgrade and have your electrical thoroughly checked so that you know it's working right, only if in that check the battery or the alternator were found not performing well I would consider upgrades before installing your audio equipment.

I guess you are not giving a lot of information but in my simplistic view just fail on the safe side and get 8ga, if 10ga is fine, 8ga will be finer. I don't think the price difference is going to be an issue.

It would be a very large cut, I wouldn't try that myself. The BP4 can be made to work is just that it will take some extra effort and time, check out the builds on here and elsewhere, usually takes months and a lot of money to build and dial in a good system.