The room is a large lecture hall seating over 400 people. The music is basically contemporary Christian music played by our worship band, plus some stuff from CD, DVD, and VHS sources. The bass guitar and the kick drum will also be fed through the system. With all these considerations in mind, I wanted to build for them a pair of double-18" subwoofers using that Selenium driver I said earlier. I know that for this application, we really need dual 18s to get great sound, or a good bass horn like the LAB. Our sound guy doesn't really place all that much stock in what I have to say, though, especially when what I say is necessary costs more or is more complicated to do than what he thinks is necessary. He's not a professional sound guy, though. He also said that home-built products are not suitable for this application because they are not backed by any warranty, and they are difficult to insure, though my friend's father, who is in charge of sound equipment for Keynote Communications, the music ministry arm of our Christian organization (Campus Crusade for Christ) has many enclosures that were built by them. The Selenium woofers I wanted to use were backed by a 5-year limited warranty, and I gave him all these reasons whyt what I would build him would be superior for the price but he wouldn't budge. He wants single 18" woofers on each side, and he wants a reputable name. That's why I am researching single-18" subs for him.
Transportation is a big concern. Right now, we have a pickup bed to work with. I think they need a covered trailer, but we have a very limited budget. Our current subwoofers are Peavey dual-15" in bandpass enclosures. They are very boomy and indistinct, which led our sound guy to the conclusion that the room was being "overpowered" by them, which is why he wants to step backwards to single 18s when we buy new subs. I think that idea is dumb, dumb, dumb, but as I said before, our sound guy doesn't really place that much stock in what I have to say. The reason why the room seems to sound so bad is because the mains we were using are Crate brand, with cheap 15" woofers and made from 1/2" particleboard material with no inner bracing, thus boomy, indistinct midbass, further exacerbated by the subwoofers' poor transient decay and majorly not-flat frequency response. I have advised him that our new mains need to use 12s instead of 15s for better midrange clarity, and that they need to have better build quality. He said that made sense.
If I could get some expert opinions saying that we need dual 18" bins instead of single-18s, and that a home-built project really is not as bad as he says it is, then perhaps I could get our sound guy to change his mind.
Addendum - yes, I do realize that bass does not only come out of 18" woofers. It's all in the driver's design and the enclosure's loading, and the SBX220 is just an example of that. However, I fear that anything from EAW is just going to be out and out too expensive even for consideration.