Indeed, 18hz is what I'm hoping for in the finished space... We shall see. So far they've acted like there's a brick wall filter at 25hz, even with no high pass filter activated.24hz is the -3db spec with 18hz at -10db
A little room gain could show more or less depending.
With dual 18" drivers a little EQ should get you whatever you desire.
Until I see otherwise, I can only report to other interested parties what I've actually experienced.