I believe I have the S18B-D
It has a port, however I leave it covered for a tighter response. Sometimes I hardly notice I have the 18, I don't turn it up too much.
I do have the option of foundation shaking bass at my finger tips but it is a little ridiculous, even for me.
I use the cross over on my F1X and only send the lowest frequencies to the 18. I could send it higher frequencies, but that's way I have 4x10.
I personally think an 18 has a touch more presence. And you can always turn it down or off to suit particular tones.
By the way, one of my favorite bands is playing at Summerfest's Piggly Wiggly Stage this week...Ekoostik Hookah on Thursday afternoon/evening. The bass player, Cliff plays an Essence. If you are going to the Fest, check them out, I don't think you'd be disappointed.
Later,
Kevin
(Message edited by kevin_k on June 21, 2004)