First Velodyne F-1800MkII in southern CO in the 90s was to me. I've had plenty of subs since, some RELs and now some SVS sealed (additional subs, sell nothing!)
Moved from one REL B1 (in theater now) to three subs: one SVS SB-3000 and two SB-2000s in my primary listening room, set at 50Hz. Need to add a fourth sub still and keep working a bit with positioning but it is much better than a single sub to my ears.
Most of the time they not particularly needed with my mains, but when low bass is on the track I hear it cleanly and with lots of backup reserve with subs set way low in volume. I'm a believer.