when I was doing measurements with rew, I could get the subs to measure flat and no ringing...the problem was this sounded like crap/neutered bass output. with a 10db shelf in the bass, I have ringing, but it sounds so much better. so I would deduce I need better subs so I can have that 10db shelf w/out ringing.
Power: Marantz sr7008, NAD C 275Bee x 2, Video: Oppo 103, Samsung 75un6300 LG oled c9 77
Speakers: Focal aria 948, Focal cc900, Klipsch synergy KSF 10.5, Magnepan LRS, Audioengine A2+
Subs: Rythmik FV25HP, Rythmik FV15HP, Velodyne HGS 12, Velodyne VA1512