Rick,

Theoretically, it is recommend to set the cross-over at the frequency 1.5 to 2 times higher than the corner frequency. Example: for m60 fc=37-40Hz and it is recommended to cross it over at 60 or even 80 Hz. Indeed, when I set it at 40Hz I do hear the excess of 'boom'. My setting is 70z. Following this recommendation for VP150 it would result at at least 120Hz.