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

I would try everything. Even keeping that position and aiming at each other . You may find only one is needed there and another in the back corner . Take one of them place it on your chair and check the room for standing waves as noted before . Then place the sub where the bass was the loudest. And keep them turned down . Or the bass will sound loose . 

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;

In my previous post seconds should be milliseconds.

Dpac996 place your main speakers where they sound best first, then place your sub-woofers. Symmetrical placement looks good but may not result in the best sound. Use the sub crawl if you can place them anywhere in your room. If you have limited placement options, put them where you can and tune them the best you can.  

Also for measurements use your main listening position. I made the mistake of pointing the mic forward when I began trying REW. The microphone should be on a mic boom, pointing up, where your head would normally be. 

Downloading REW is free, you do have to join the forum. REW comes with a test tone generator that will sweep all speakers or just subs. The results from the sweep can be displayed in several ways. You won't need an O'scope. There is a learning curve and some equipment to buy but there are several tutorials available if you search. There is also a forum where you can ask questions. 

Good Luck!



        

I have 20.7 Maggie’s running full range with two stereo Kinergetics sub towers of 5x10” subs and two SVS 16 Ultras. When I hooked up the Ultras to complete my sub array I scared the s**t out of myself and literally jumped off the couch as my stomach flipped, water rippled in a glass on the table, wife jumped out of the shower and yelled about the thunder that was shaking the house to turn off the stereo due to the storm. That was out of control bass and what I suspect is the issue for a lot of people with integration.

I have a fully active set up with a Mini DSP, used REW with an Earthworks +-30k to measure the speakers and room. I followed the tutorial and used my own data in MSO and made 12 biquad filters per channel (8 of them) to optimize the room and have reached sub bliss. It is absolutely perfect and there are no modes.

I had a friend over for an extended listening session and they asked to take the subs offline because the 20.1’s are full range. They couldn’t believe the difference as they couldn’t “hear” the subs but not being on made a world of difference. No room for the subs as I read above? Make them into end tables like I did. Very WAF friendly with a 1” thick piece of glass on them. Guests have no idea they are speakers. 
If you can take the time to do it right with a sub array (four is the minimum in my opinion) you won’t regret it.