FWIW...
I did a show on Saturday using the Seismic 15" passive coaxials in a small PA rig, on tripod stands. Sort of a "make or break" minimalist gig for the Seismics. The gig is 2 vocals, acoustic and bass guitar, and occasional drum beat box for the post-dinner crowd. Usually we would put only the Acoustic and 2 vocals into the PA, and then have bass and drums run through my FR stage rig so as not to bother the FOH (a Fender Passport) with PA set up even with the vocal line, with no vocal monitors. I've never been happy with they way it sounds there...too disjointed...so...
I decided to go with running everything into the PA (Seismics, powered by a Crown xti 4002, 2 channel stereo, full range) via my Mackie 1608 digital board, and with the speakers/stands strategically placed so that they are behind us, angled in slightly, so as not to feed back, but so we could both clearly hear the entire mix from out of the 2 cabinets. For an acoustic gig like this in a small-ish venue (80-100 peeps), in a very long, narrow room, the sound coverage is difficult. We set up facing the "short" wall, which is probably no more than 18 feet wall to wall, if that. Good sound is kind of tricky here.
Long story short is that this set up worked very well, though it required a bit of corrective EQ for both the speakers and the room, but all in all was probably the best mix we've had in this room, ever. It was better balanced because we could hear everything in context, and since the PA speakers were behind us, we didn't need to strain to hear vocals or instruments alike. Typically, with the speakers placed even with or slightly in front of us, with no monitors, we would only hear the vocals rattling around the room off of nearby glass wall panels (yuck!), and the discrete bass/drum rig would dominate the stage mix. Also, with bass and drum content, the 15" speakers handled both with ease and clarity (thanks to channel compression) without breaking up at all.
I guess the moral of the story is: the Seismics aren't too bad of a deal in some situations, but it always helps if you have a couple thousand $$$ worth of gear feeding them to bring out their best.
