Actually, although I have a great deal of respect for what the 18 can do, I haven't had any real need or desire to own any. Always got the job done with 15s, and more recently a couple of 12" Eminence neos that deliver boatloads of bottom.
When EV came out with their SRO speaker line in the late 60s-early 70s , they had a 30" version for a short time, that was beyond belief in delivering bottom. The only bass player I ever saw use them was Larry Taylor with Canned Heat. 4 30" speakers in reflex cabs that were about the size of my first apartment
. He powered it with a stack of Sunn heads (probably 200S). He was so low and powererful his sound did not really hit your ears as much as it hit your body. It would make your belly and butt vibrate....Beware the Brown Note
.
Awesome sound , but sure as hell nothing you'd want to tote around.
Rick