Eh hem!...Subwoofers... What do ya know?

@erik_squires 
Can you detail this thought please:
"Speaker level inputs are subject to the amp/speaker impedance matching"

My amp's Zout is much less than an ohm (according to Luxman the damping factor is around 700);
The Zin of the powered sub, according to JL's manual is about 4,500 ohms; 
The back EMF on the speaker cables should be super low, as the speaker "sees" a super low "load" across a very low DCR speaker cable;

If I was using an amp with high Zout (say 1ohm), then I could do some math and find, possibly in the 30-100hz region a reactive speaker impedance appearing to be "real" resistance of a similar magnitude to the zout of the amp, then causing a voltage drop the speaker sees, basically a frequency dependent voltage sag; 

But how would, even in a high output impedance amp, this affect the signal at the amps output eventually reaching the active subs 4.5K zin? 

My main concern about taking the signal to the sub from the amplifier output terminals, is the time delay that can never be made up by any adjustment in the subs crossover settings; I could delay phase by a full 360 degree to align the peaks, but i'm actually off a whole cycle. This seems bad for impulse response, bass drum hits, bass guitar lines, etc, might be perceived to be "fatter" but smeared. I don't know, maybe i'm going off in the weeds here and none of this actually amounts to a loss in perceived fidelity at the chair; I guess I will find out soon enough. I can see myself diving into the active crossover just because it seems so elegant and proper-- here we have total control over the timing latency and sub/main handoff;

Cheers

pretty solid article on sub integration.
https://jlaudio.zendesk.com/hc/en-us/articles/205061040-Adding-a-Home-Audio-Subwoofer
I am preparing to integrate a pair of JL E112 subs in my system...showing up in a few days...
I will first try high level connection right from the amp terminals to the subs HLE input...then try a Jensen Iso-Max speaker level to line level isolation device...I think ultimately though the JL CR-1 (or similar) the ideal solution for integration mostly because the latency can be better controlled;

I initially plan on placing them like this (on the insides of the speakers);
https://imgur.com/Paj46Ti

feedback welcome!

@erik_squires thanks good info;

I agree the using a pre-out (or active crossover) the preferred way and so does JL audio, but in my case I am running my XLR only DAC directly into my Amp; I will need to play around in the speaker level input regime until I either get an active preamp or the JL CR-1 (preferred);

I actually sold my preamp because I found no real advantage using that vs DAC direct; So, with those funds I diverted into the JL subs and some cables (I digress); Now, it seems that plan was half baked and I would have been better off keeping the pre and stretching the budget to get the subs but I'm already way over my audio budget for the next 10 years, lol

Anyone: please take a look at my setup; do you think the subs should go on the inside or outside?

https://imgur.com/Paj46Ti

-Cheers

Good idea davekayc
Keep all options on the table!!

The JL E-112 subs have a fair amount of built in tuning so hopefully this proves helpful;

Since I am nuts about this stuff, I am going to grab our nice Oscilloscope from work and my omni mics (or use a Laptop with some USB mics) and capture the onset of various test tones;

Once I have alignment temporally (overlapping first cycles of sine wave) and magnitude wise, I can play with the sub gain setting if the actual listening test prove excessive bass or what have you. I think the sub/speakers must align time wise for max potential, at least this is what I have read and it makes sense, on paper;

I was going to place a mic directly in front of the sub 3 inches away; same for the speaker woofers mic;
Cue up some bass tracks or just a sine test tone, trigger the scope on one mic and see how they line up. I am 100% positive if I run the sub off the amp output; the acoustic rising wavefront (the first cycle) will arrive at least 10 ms after the rising slope on the woofer output, due to the delays in the sub;

I will repeat the test at the listening chair to see how the alignement changed after wave fronts traveled 9 feet;

Once the entire room "pressurizes" does this time alignment still matter that much? -- we don’t listen to successive impulse trains...we listen to music in a complex environment with lots of interference patterns;

I can, in theory adjust the JL phase to exactly overlap the sine waves but the sub woofer will always lag the speaker woofer by a whole cycle. This may mean absolutely nothing  sonically, or it may be perceived as muddy or too fat.

It’s going to be a fun few weeks figuring all this stuff out!

If I end up hating the subs / can’t get them to gel, I guess I can toss them in our home theater or sell them;