Joe X

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.

If what you want is some low end AND not to have a bass less system your setup will probably do.. or maybe you will be back as it often happens. I always suggest people to get a large enough system for the vehicle in question mostly to help avoid them go multiple upgrade cycles which are more costly in the long run.

A single 12" sub is too small of a setup for an SUV, to improve performance, the box should fire back and be close to the rear gate. To me a couple of 15s in a subs up /port back configuration should be minimum in such vehicles to get decently loud.

The amplifier you have is class AB with efficiency of about 55%, if you want to deliver 1400W with that amp you are going to need to source: 1400W/0.55 =2545W That means you will need full electrical upgrades and the amp is going to get hot as hell if pushed to the limit. It was in the 90s that class AB amps were used on subs.

So here is a suggestion, power: to sub(s) rated, amp subsonic filter to 28Hz, minimum port clearance 2 1/4", 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: box ideally suited for sedan / hatchback

Only if your scope connected to the amp POWER input terminals show sudden voltage drops that go below 12.5 volts, if you don't have such drops you don't have to do nothing. Best of luck and if you have any questions let us know.

One possibility is that your subs are still on the break in period and need a couple of weeks for the suspensions to loose, yet you can use the scope to see how stable is your input power at the amp terminals, even If the voltage drops for less than a second to less than 12.5V you can be having issues, those full bridge amps are a problem anytime your electrical is not perfect, even if your ground is not exactly great or any connections are not so tight problems can result even if your electrical components are good, if you did not do the big 3 you should do that immediately.

Great infos on your system and I get you are fighting rattling but still don't know what is your vehicle model and pics would be great.

You will not experience loss of sound quality on the sub by running at 2 ohm, THD+N is rated the same at 4 and 2 ohms and you will be driving the sub closer to what it expects. Honestly only cheap amps with deficient power regulation could perform worse when being used on a lower impedance load, Alpines is not the case, it could run hotter in any case if pushed hard, you prevent that with proper installation with great ventilation and maybe a fan nearby just to make sure if it became necessary.

That amp is a single channel, the extra terminals are provided for ease of use. Check out my previous reply.

Actually no, if you wire coils in series you get 4 ohm, one sub per amp and you will be sourcing 1000W to each sub nominally (look at the table I left you above) but since rockford fosgate are under rated I am pretty sure you will be getting like 1200W to each sub.

Parameters need to be selected in their page, you know you have the correct parameters if Sd = 1210 square centimeters.

Those amps will give exactly the same power connected to 2 ohm as they give connected to 1 ohm, you need to do nothing, here is what the amp specs say: Same 1500W at 1 ohm or 2 ohm. Only if you connected to 4 ohm you would get less power.

The power 1500bdcp is a constant power amplifier, wire each sub to one ohm (coils in parallel) and then connect one sub to each amp to get 1500W to each subwoofer and you are done.

Check that modeling: Fi 4.11 18 Sundown Zv618: Both based on a 7 cubic feet net @32Hz enclosure. The Fi has a 4 dB advantage over the Zv6 at their rated power and justifiably so since the Fi is a 4500W driver vs 2500W. Check out your fi parameters, I am sure you picked the 12" driver parameters instead of the 18". It is very easy to make a mistake with modeling software, so easy many people don't rely on modeling.

I don't know that worst loses happen in glass windows, rather it occurs in large thin metallic parts like the roof of large vehicles or where ever you se flex happening, Any place you see flex happening you need to apply deadening. Anyways when you have a system level issue you need to post what is your full system components, your electrical (including wiring) and what is your vehicle, your box specs and a lot of pictures. Lastly a wall is not a box firing forward subs and ports, what a wall does is reducing the cabin size, increasing output significantly, a box specially in the middle of a cabin firing forward will probably do worse than a properly placed subs up / port back box.