What are the best subwoofers you have heard for music. Speed, Musicality and integration

ATC C1 MK2 subwoofer : choice of real wood veneer cabinets, premium hand-built drivers, and ATC’s standard 6 year warranty. Highly recommended.

Best of breed in the up to $4K strata, that I auditioned (and bought) to complement my HARBETH speakers.

https://www.theabsolutesound.com/articles/atc-loudspeaker-technology-launches-c1-sub-mk2-active-subwoofer/

https://www.whathifi.com/news/atc-launches-compact-c1-sub-mk2-active-subwoofer

Gallo TR3

Does anybody have a theory about what specifically makes REL subs integrate so well?  I've never heard one.  Bottom firing subs tend to have more even in-room response.  Subs with smaller woofers have less visceral transient responses that may mean they draw less attention to themselves.  If they know some secret nobody else does they're not going to advertise it because that would be stupid.  

Having two in my system that integrated very well and fairly easily, I would say using the Speakon high level connection helps tremendously.  They get fed the same signal the speakers do.

calvinj

REL is the best Sub in the business. 2nd is Sunfire (smaller in size yet still packs a punch (no pun)).

Happy Listening!