Sub amp plate that cross over at less that 30hz?


I have seen lots of sub amp plates, but all them seem to cross over at 40hz, but not lower. Can anyone point me in the direction of a sub amp plate that will cross over below 40hz?
matchstikman
revel B15 sub has cross over points at 30,40,50,60,70,80.ook up revel speaker web site for full details
What sub would you cross over to at 30hz.You're talking one octave if you have a world class sub.
The 500 and 1000 watt plates, available from Partsexpress, have variable Xover from 30-200hz and variable EQ from 18-80hz.