Joe X

Entering those dimensions and assuming you used 3/4 wood and using a 10 long 3" port I get 2.1 cubic feet net or 0.35 cubic feet per driver, they specify 0.12, also one 3" port is 7 square inches of port area for all drivers while CT is asking for 12 square inches PER driver. Your box is completely off spec. Also modeling subs parameters reveal those subs will never get decently low in a ported box among other things due to very low Xmax. So you can go ahead and build the correct box for them and still get all poor low end.

If you mean higher Fs means it won't get lows, the answer is a single parameter isn't enough information to reach any conclusions. You need to model the sub in the box you intend to use,

You can also setup your gains low making sure power delivered is within drivers specs. No one is to say if that distorted signal will make any difference, It's all about being prepared to prevent a bad outcome. Much luck and if you have any other questions let us know.

You can get Brazilian "pro audio" mid woofers with some super bullet tweeters, that will withstand much more power than standard speakers, brands like Timpano, DS18, PRV will serve the purpose, even if you managed blow them they are inexpensive to replace. As you say it is an odd request so don't ask me if I recommend this or if you will suffer hearing damage from listening loudly to that or not.

SUV boxes are generally subs up / port back, subs / port forward are for some trunk car designs and walls.

I don't remember anyone using those subs ever on here. They are rated very low 150W RMS power, People have asked about iDQ and iDMAX series in th 12" size usually. Looking at the sub params 0.9 cubic feet net will work up to rated power, nothing more and the port area that will need is 3" round port PER driver, if using 2 subs in the same box you can use a single 4" port for both or two 3" ports. As for if these blend in with the JL comps, I am pretty sure they will, the mid woofer of the splits will reach plenty low being the 6x9 size just pick a 70-80 Hz crossover point.

Your enclosure is completely and totally misdesigned and misplaced and likely the reason your system is not performing as it should. The best way to get loud is through cone area NOT power, Get 2 15" subs in a correctly designed enclosure instead of 12s and you will see much higher output even if no extra power is added, "Cone area is King" that is no joke. Also the quality of the subs is extremely important, use subs with strong motors, higher Xmax, higher BL not some weak mini motor subs. The amplifier and electrical including wiring are chosen AFTER the subs are chosen not before, The largest amplifier you will need doesn't need to be more than twice the RMS power of your subs, more than that is just wasting money.

You have grounding issues, check out the video to learn about the different issues: https://www.youtube.com/watch?v=Q8dpucdxs6Y If you can't find the issue go to a pro installer.

Regardless of the issues you may have two 12s in such a big vehicle is too little cone area for such a big vehicle, SUVs need at least 2 15s in a highly efficient enclosure to get decently loud. Of course if your enclosure is bad and / or your installation / settings are no good performance will be bad regardless of what you own.

If you want to experiment more those modules are only a bunch of resistors even if they sometimes are packaged to look like a chip, you can make those modules yourself to any frequency you want, audiocontrol keeps a pdf that tells you what resistor values you need.

Such an old device that used those pfm pluggable resistor packs, who would trust a non soldered connection maybe 40 years old. The subsonic in the epicenter should be enough in theory even if they are 18dB/octave only but using the amp SSF as a safeguard can't hurt anything. Your call really.

1.5 cubic feet net on rated power. I need t/s parameters to tell you more.

At least 2 6" ports for the 8 net box BUT slot port makes sense in this case, sub up /port back.

Post maximum dimensions for a box inside your trunk and state if rear seats fold down in your car.

Alright best of luck!

Your net box volume is too high, it will play very peaky and lower sound quality (higher group delay), 2 net is maximum, port area 28-29 square inches is more than enough, larger port area than that is useless, the port gets longer and your external box size gets unnecessarily big, the longest port length I recommend is about 40 inches to avoid in-bandwidth port quarter wave resonances. I have found that with skar subs their larger size box recommendation is about right, unlike many manufacturers that suggest tight enclosures than what they should because most people prefer smaller boxes. So 2.0 cubic feet net with 29 square inches of port area tuned to 32-34Hz is what would be my suggestion.

Ok, you should find your maximum clean signal volume of your head unit with the DD-1, at the RCA output of the LOC you should make sure that the "maximized" light is not blinking, should be completely off, the output voltage of the LOC should never be set above the input voltage of the amp, I guess I will agree that 5V Rms that you measure with the multimeter should be fine, Then you use the DD-1 connected to the amp output and set the amp gain making sure the DD-1 shows no clipping. If you use bass restoration available on the LOC test engaging in it during the gain setting procedure, making sure no clipping ocurrs.

Make your own thread, disconnect the RCAs and set the amp gain to zero and turn on again, hopefully no clipping will be present, also disconnect the bass knob if you use one.

Post pics and specs (box specs, amp, electrical, etc) of your previous setup, Sure enough the X subs are for the lows and not SPL but two 18s (if properly setup) should not be so disappointing unless the box is wrong or the subs are not driven properly.

You can setup a virtual machine in your mac to use windows on your mac, check out the virtualbox software. Once setup you can run Torres software. https://www.virtualbox.org/wiki/Downloads

Open up the rear deck to let sound waves into the cabin. That is going to be half of the fix. Would need all the details of the box design you have (all internal and external measurements) to tell you if the box is a problem but 2 cubic feet net is pretty standard and should work, the amp is a little weak but nothing that would make a great difference. If opening up your rear deck is not enough I would go two 12s, probably better ones if possible.

Never mix sub sizes in the same box, not ever.,

That's correct but bear in mind that it is just a rule of thumb and it may not be adequate in a number of circumstances, for example: 1) you are applying a lot of power. 2) suspension characteristics of the sub. 3) box volume / port area. 4) your actual tuning is not what you think. 5 ) audio processors specially if improperly set. 6) many others. A better way to get your SS frequency is measuring your actual tuning of the box you built and software modeling checking the excursion plot and making sure your excursion stays below Xmax.

If you are looking for sound quality probably you want Mosconi, Arc Audio, Helix or such kind of amplifiers specifically made for sound quality. But if you insist on getting non sound quality specific amps like those you mention then in my opinion pick the cheaper solution, the two jp34ab, class AB amps. Usually class AB amps outperform standard class D amps in sound quality and it seems to be the case here as the AB option has about 10 times less THD as the class D if you look at the specs.

The sub itself may barely take 1000W RMS on music no more, If you want a sub that can take above rated look for sundown, fi and such.