I'll chime in, rather late 'cause I'm new here, that it's not really about loudness in the dread vs. jumbo debate.

The materials used and the shape of the body will create the tone of a guitar, while the bracing and construction create loudness.

Jumbos typically have huge low end, created in their much larger lower bout. Highs & upper mids are created in the shoulder area of the guitar, again probably more accented with a jumbo's curvy shape and wider shoulders. Midrange, to simplify, just kinda happens between the two, but a lack of mids opens up frequencies for the human voice to occupy - hence so many famous singer-songwriters being absolutely in love with their guitars - their voice fits the space not booming from their axes.

No time to discuss tonewoods, but I will mention bracing and construction. The reason Martins, Taylors, and other fine guitars boom out the noise is their impeccable interior bracing. it holds the front, back, and sides together while allowing it to reverberate harmoniously.

Hope I didn't sound too know-it-all, but I'm a self-admitted TOTAL GUITAR SLUT - sorry, *ahem* collector, and I could babble about them forever. That's why I'm good at my job!