Joe X

So here is a suggestion, power: to sub rated, amp subsonic filter to 28Hz, minimum port clearance 4 1/4", figure is just an assembly guide:

As a first step disconnect signal at the mids and highs amp and see if this disconnected but powered amp still shows the noise.

Your power cables into the loc are of the same color and your speaker cables as well, that usually lead to disastrous results. Get some help from a professional installer.

7 cubes net not possible on those dimensions, I am sure you can go wider and taller in that vehicle, preliminary calculations shoe a maximum of 5 cubic feet net is possible for a double layer box and about 6 net for a single layer with double layer baffle is possible (heavy bracing).

Your figure is missing port dimensions of with and length so I cannot tell you if the design is correct, what is obvious is lack of necessary bracing, As for the wood, any stiff decent quality wood will do, MDF is relatively less expensive and that's why is used more.

"music was playing on the radio and WITHOUT RCA’s" If you mean that the amp was playing music without the RCAs connected then your car is possessed most definitely, you could start throwing some holy water around and see what happens, if the amp keeps playing like that then you are in big trouble.

Yes sorry I misread the specs BUT its the same you just wire coils in series, subs in parallel down to 2.66 ohm and you will get 1200W to the 3 subs. You won't get any less power than 1200w because it is a constant power amp, in normal amps you wire down to the lowest impedance to get the most power but not with this one, also will deliver 1200W regardless of the input voltage (12V, 14 V) unlike normal amps.

You got it exactly backwards, the HD1200/1 will give 1200W at 1.33 ohm bu the RD1500/1 will not give 1500W at 1.33, it will give less, I wouldn't recommend getting the RD1500/1 at all unless if you like how it looks or something like that, you won't get louder at all. As for the alternator the 220A one will suffice for either amp no problem as long as you don't play continuous sinewaves as you say, just music, that includes the car services and a mids and highs amp 400-500W RMS, just do use well installed quality power wiring for your amp or amps.

If your amp is rated above 1000W RMS you also need a HO alternator, batteries and wiring are good upgrades but what makes energy is the alternator. Feel free to check your subs but since you say the final impedance of 1.4 ohm has not changed likely you will find everything in order. A small upgrade you could do is getting a voltage gauge and connect it to your amp power terminals, with your car on and on the road your voltage should be about 14 volt and should not dip a lot when the bass hits, if you see 12V or less and 2+V dips then you electrical is dying and needs

Was away for a few days so a bit late, let me know if you still need the assistance.

For some reason Sundown did not provide an X10 design so here it is for you and for whoever needs it: Same style as Sundown's X12 design. Will fit most trunk cars.

Do you have any electrical upgrades? systems above 1000W of power need upgrades, a high power system without upgrades will start under performing (getting less loud among other symptoms) overtime and at some point that electrical system will fail.

In a van generally you benefit from a subs up / port back type of enclosure.

If listening to rap and such go for a 35Hz tuning or less, if you want fast bass avoid building a larger than recommended box, keep it average to slightly tight. Ideally modeling software can help you find a good balance for a specific sub.

I would recommend you to temporary place your tweeters in different locations and see what you like, bear in mind that tweeters installation angle is also important not just location.

If you are running 1200W you would need 2400W to gain 3dB which is a very discrete gain i output, it is safe to say that 300W will not be a compelling gain in output if it is discernible at all. Also the RD1500/1 will only source 1500W at 1 ohm, at 1.3 ohm will source less so your expected 300W gain is questionable,maybe 250W, 200W or less? What I would recommend is checking your electrical and your gains to be optimal, improper electrical can ruin both output and sound quality on a system. If those fixes are not enough changing to a sound quality specific ported design could vastly improve your output, 3-4 dB without sacrificing much sound quality.

What is the vehicle you have?

By going from 15s to 12s you are losing a lot of cone area, even if the 12s are on ported you won't see a meaningful gain in output. Modeling both options could give you a clearer picture. If you do a couple of Sundown X 12s on a 4.5 net box and a 4K+ amp then you will see appreciable gains.

I would use the same brand of amplifier brand you are going to use for your midbass drivers, use a DSP to match time alignment if the location of the drivers is going to be very different as the midbass drivers, also the same goes for the tweeters, same brand of amp. Just bear in mind that the drivers are 8 ohm, maybe you want two sets to lower impedance to 4 ohm per side. As for the drivers themselves, I don't know that PRV build sound quality drivers such as morel and the like, to drive would be SPL drivers to SQ results, if I understand right you need to drive them in their linear region both frequency and amplitude, that would probably be 250-2KHz and 75% of their rated power, maybe you should talk to an SQ specialist. In any case you want to get a high quality DSP, also amp selection involves auditioning, class d amps for mids and highs can be noisy, I would feel safer using class AB for full range amps, at least if you are picking something inexpensive.

Seem a bit concerning to me that those will play midbass pretty poorly. You can see that at 100 Hz these are already about 4dB below baseline. Also note that these are 8 ohm parts most car amps are optimized for 4-2 ohm. As for the amp you should be more specific, any 500-600W rms @8 ohm full range stereo amp that has a high pass filter should work BUT not sure what you mean by best, you want class ab, d, small, SQ?

WinISD do not support slot ports only non slotted, the box pro site I checked only once and tuning was somewhat off, the tritricum calculator is for people that won't use modeling software, if you did enter correctly the data into WinIsd and you got 25 m/s then you are ok but honestly more than 50 square inches for a single 12 sounds high, unfortunately don't have the parameters for your sub so I can't really verify.

Actual numbers depend a lot of usage, you need to factor in amplifier efficiency, mids and highs amp and car services, if you use frequently your system at high volume (only daily, not for competitions) a 220A alternator, obviously you will need to have subs that can take the full amp power, you should also upgrade the battery to deep cycle, your battery needs also depend on how much you usually listen with your car off and how much time you drive your car everyday.

Still the stock connection between your battery and the alternator should be upgraded as a part of a big 3 upgrade. Also try to tap into a signal that carries the sum of the left and right channels or a LOC that will mix left and right for you.

Don't know if you tried to change the jumpers in your JL Audio crossovers to -3dB, that would considerably lower the level they play and maybe you don't need to change anything. Also you could audition the C2, C3, those if I remember right use soff dome tweeters.

You will have to run power line to the amp, if you are going to run 1000W you will need a 4AWG wire, also consider a 10" sub, box size is almost the same size but a 10" is louder than an 8" on the same power. 8" subs exist to be placed in underseat enclosures in trucks because 10s wont fit firing forward.