I think from memory that the the keltic and kaber mid range xover is not a band pass design ie there is no high pass section to it ,so it will not filter off the low information being fed to the unit .When they say its 118hz they mean that s the the midrange driver /cabinet ie system roll off starting point.
Try adding a 50 mfd non polar cap in series with the mid unit, that will prevent it excursing too much.
Try adding a 50 mfd non polar cap in series with the mid unit, that will prevent it excursing too much.