Best Subwoofer Connection for Music

@m-db I haven’t gotten that far yet on this go-round. In the past, I’ve placed the sub in the listening position and gone around the room to find the spot the bass was strongest. The Dayton-Amped 15” sub for the McIntosh system is headed for the #1 ‘sweet spot’ in the right front corner; the 10” RCA sub with the Rogue system will go to sweet spot #2 in the left front corner initially. The Sound Doctor (see ditusa’s link on first post) suggests that placing a second sub in the back of the room may be desirable. I’m just trying to get one per system up and running (correctly) before experimenting with a second sub. And I would likely try that in the upstairs listening space first. Good question, though. 
 

@panzrwagn The experts agree with you, see ditusa’s link in first response post above. I have a capable active crossover that I’m itching to use, a vintage Pioneer D23, so I have what I need to implement your (and the expert’s) recommendation. I’m going to try it without the crossover, and then with it. I’ll let you know how it works out. 
 

All: To anyone stumbling on this thread, Panzrwagn’s pronouncement is, indeed, the best way to connect a sub: using low-level connections, optimally downstream of the best active crossover attainable; although there are many options short of that that are all an improvement. As I’ve noted several times above, ditusa, in his first response to my post links to a rather complete treatise on the topic by the Sound Doctor (his name is given in the link) who has worked in field for over 15 years [probably 20 years now] and spent enough time with JL Audio to develop the finest crossover for the purpose in the industry (according to him). I found his writing style quite approachable. He recognizes that integrating a sun is NOT an easy task, but he explains WHY it isn’t easy and what can be done about it. If you’re interested in the topic of this thread, I recommend highly reading it entirely. 

@oldrooney   "I haven’t gotten that far yet on this go-round. I’ve placed the sub in the listening position and gone around the room to find the spot the bass was strongest.'' 

Determining your rooms actual standing wave bass modes using a sub placed at the listening position playing low frequency cadences. THEN locating the loudest bass modes is actually the very first step in setting up a -3dB subwoofer system.

There the subwoofer/s use the rooms modes requiring the least amount of their power and processing needed for their best performance, integration and the musicality designed during post production.

The room rules, not the system. Good luck with it.

@m-db Thanks. I feel that I will to develop some skills along the way because despite several attempts at integrating subs, I haven’t been able to get lucky yet. And you’re right about the room ruling. I’ve got two completely different systems set up in the same room, and guess what? They sound virtually identical. The average living room is indeed a limiting factor that even acoustical treatments can only mitigate, but not remove entirely. The Sound Doctor makes that point before all others, I believe. Thanks for the response. 

@panzrwagn and others, I think I’ve figured out why some people are recommending the high level connectors, provided that the sub has high-level out, as well. If the full range, high level, signal goes to the sub first, the sub applies a low pass filter to the signal for the purpose of selecting the frequencies for its low frequency driver; but it sends the remaining frequencies (low cut = high pass) out the high level speaker out terminals to the main speakers. So the effect is the same, separating low frequencies from the main speaker and sending them to the sub; it’s just that the means are different. I’m sure that filtering is best done at the low level, but would suffice for testing out the theory. 

@oldrooney Yeah, but that's not how it works. Opening up any subwoofer with high level inputs and primary speaker outputs and you'll see they are just passthroughs tapped to feed the subwoofer amp. Hi level inputs typically have a high impedance value tap across which the signal voltage is measured, then padded down to line level which feeds the subwoofer amp and it's LP crossover. The high impedance presents no meaningful load on the main amp, and the full range signal continues on to feed the primary speakers. 

Doing what you suggest would require some very large value and thus very expensive capacitors and coils just for a single fixed frequency and would likely impact overall sound quality of the primary speakers.