There are actually experts in audio design that can compute the size and shape of the enclosure needed for a given speaker or speakers. Some of the best examples of big sound from tiny speakers are the laptop speakers. They come in all shapes, and many of them are also ported to enhance the sound. It's actually pretty amazing the "big" sound you can get from a one inch or even smaller speaker!
I do know that my personal experience has been for really good bass, a somewhat larger enclosure is usually best. I just experiment with the speaker/baffle combination until I get the best sound I can.
