Wow! Turns out I have one of the 2 S18-3's that were at the DMP showroom. They have very high efficiency. They were powered by a custom power amp that I constructed using surplus Sansui driver boards and later by my custom Mac clone.
With many of the current PA's and stage monitors being too bright these speakers have incredible tone, wide range, and lots of punch.
They sell used for around $200 to $400
B.C.