Jazzy you are correct, it is probably even better not loud, because bass being omni-directional gets lost the farther you get away from the speakers especially the real low notes. That's because it's hard to move the air in the back of a room. That's why a bass has to have three or 4 times the power, and much more speaker surface than a guitar, which is directional and cuts through without having to move the air. When you go to a concert at a very large venue, they always have literally a wall of woofers and thousands of watts driving them to the point that the building shakes so that the bass is heard and felt (you can feel bass that you can't hear) throughout the venue. With that said that's where the 18's come in, they move air at high or low volume and at low volume if you don't have enough speaker surface the low notes will fall off pretty quickly.
I had a chance to see Stanley last year at a venue with a real high ceiling that seats 1600, and he had a rig similar to what you described. He was able to fill that venue with bass without playing loud. He does use two different amps for bass guitar and acoustic. He uses an Ampeg SVT 4pro (bi-amp) for splitting his high and low pickups on his guitars, and a SVT 2pro for his acoustic bass. The little fender amp covers the high frequencies on his tenor and piccolo basses. I've rambled enough, but in my opinion for what it?s worth an 18 or 15? with 4x10 is a great combination to cover the full spectrum of frequencies that you can get with an Alembic bass. BTW my SVT 4pro is in a rolling rack case because they are pretty heavy.
