What is better 1 bigger sub or 2 small ones

According to the book, "Get Better Sound", 2 are required for accurate imaging, and all the old saws about how bass is non-directional are beside the point.

Lloydc,

Theoretically that is true, but for the lowest audible frequencies that a sub would deliver in an already mostly full range system, how much it matters practically is debatable I think.

That using more subs enables smoother bass response throughout the room is a significant advantage nonetheless, if that matters. 4 is even better than 2 and 2 is better than one and the results in most cases should be clearly audible. Audiokinesis is the vendor in these parts who designs some of his speakers in a modular manner that allow for this by design up front.

Its complicated, as all of life is. I have two, which I started with. Felt one would never tell me if two were not better. I am happy.

Can 2 overload some preamps?

I use two REL subs, which are positioned close to each speaker. It's important not to 'overuse', and spend time working on intergrating them with the speakers.
Finding a good dealer to help you put them in will reap huge benefits. I used Tim at 'Tone of Music' in San Francisco, and love the transformation that adding them provided.