How about all of them, aka pink noise? Cheers,
I've found that to get a REL sub right is to simply find out what your main speakers are doing…i.e. where their lows actually go (speaker specs aren't always accurate) before running out of gas, and I use a Stereophile test cd for that. I adjust my subs to start in around that frequency and…I can't make this point enough…use your ears to get them to sound like YOU want them to, which requires putting them in the part of the room that works best. Note that I still turn the level up and down here and there relative to the recording I'm listening to (I have "chicken head" knobs on the level pots on both my RELs to make this easy). Music is by far the best way to see what music sounds like…who knew?