My transmission-line ported Vandersteen 1Cs are rated to be 3dB down at 38 Hz. I got excellent integration of my Titan II LE (located slightly forward and to the right of the Vandys) with the sub's crossover set 24db down at about 40 Hz.
Mostly because of power handling concerns about the Vandersteens (when I wasn't around), I got ACI's 65 Hz passive filters for between my preamp and amp. I turned up one of the Titan II LE's crossovers to somewhere between 55 and 60 Hz and left the other crossover at around 40 Hz to achieve integration that's at least as good as it was before. It also resulted in a slightly improvement of the upper bass and midrange from my 2-way Vandersteens. There is increased open-ness and "air" in the music.
Mostly because of power handling concerns about the Vandersteens (when I wasn't around), I got ACI's 65 Hz passive filters for between my preamp and amp. I turned up one of the Titan II LE's crossovers to somewhere between 55 and 60 Hz and left the other crossover at around 40 Hz to achieve integration that's at least as good as it was before. It also resulted in a slightly improvement of the upper bass and midrange from my 2-way Vandersteens. There is increased open-ness and "air" in the music.