A test CD came with my HSU subs and this was interesting to use. I would suggest you can't calculate a proper crossover frequency as room modes will rule the day. Room placement and your ears are the best place to start. Then if you need to confirm all is well a test CD can help.
-6db vs -3db speaker roll-off for sub crossover calculation?
My ATC speakers only list their frequency roll-off as -6db at 48 Hz. All the guidance I can find from SVS and other sub info sources use -3db to determine settings.
Help!