FYI:
Long story but I picked up a pair of REL Carbon Specials recently.
I have been trying to get them to sound properly, trying to eliminate the "rumble" that comes on certain songs and tighten up the bass.
Mistakenly, I put the phase switch opposite one-another.
One on Zero and the other sub on 180.
Cleared up ALL the rumble and gave me a nice clean TIGHT bass.
Speaking to an expert on subs (not associated with REL) he suggested a 4 way sub setup, where each cancels the other.
Stated that the best way to adjust subwoofer resonse was using a phase dial (not a switch) Similar to the Swarm subwoofer set-up
https://www.youtube.com/watch?v=KIY4bBrJBx8
http://www.audiokinesis.com/the-swar...-system-1.html
file:///C:/Users/fam13/Downloads/SwarmGoldenRatiosSetUp.pdf
I have not tried this layout before.