Are the JL Fathom subs really that good....

The easiest way to get a seamless integration and reasonable phase coherency throughout the room is to use two matching subs placed adjacent to the main speakers. I have something similar now with my Mirage OMD-15 towers and MM8 subs.

And the best most seamless sub/main integration I've personally heard was a pair of JL Fathom F212's flanking a pair of Magnepan 20.1's. There was no discontinuity in timing, timbre, tone, nor noticeable nonlinearities by frequency.

NVP: All very good points. I was thinking more in terms of getting the easiest in-phase blend wherever your listening position. With a sub in a different place than the the mains, the phase relationship changes as you change listening positions. But as you say, the subs may need a different position for smoother response and better room coupling.

In my own setup I have a compromise between the two. I run a stereo pair of subs, but they need back wall reinforcement for any meaningful low bass, so I position them as stereo pairs against the wall and directly behind the R-L mains. That way I get the room reinforcement and only have to adjust the phase control a little bit, and the frequency range stays pretty uniform throughout the listening area.

Another advantage of separate subs is that the mains and the subs can be built and optimized to their frequency ranges, and it keeps the internal vibrations produced by very low notes (and contained within the sub) from smearing the cabinet vibrations handling the midrange and treble.

And I meant to add, "Yes, JL Fathom subs are really that good." My local high end dealer carries Wilson, Magnepan, B&W, Vandersteen, Vienna, Wisdom, PSB, Meridian, and for subwoofers ... JL. They do the best electrnoics/room/cable/speaker matching I've ever heard from any store over the 40+ years I've been hearing demos. They could carry any brand sub they want but chose JL, and their setups have proved to me how seamlessly JLs can be blended and how they augment the soundstage and presentation to a higher level of musical involvement, dynamic range, imaging, detail, you name it.

If they'll blend like that with Wilson, Magnepan, Vienna, Wisdom, and Meridian, they'll probably blend with pretty much anything.