One of the groups I play for, a renaissance-faire-friendly folk act, is considering investing in an acoustic bass guitar, for both amplified and unamplified use. However, acoustic bass guitars have a rep for being useless when they're not plugged in. (This seems reasonable. Keep in mind, a double bass needs a bigger body than a violin to produce audible sound.) 

I owned an inexpensive one many years back that certainly lived up to this. However, I have heard that some rare instruments of this type *can* be loud enough to be heard over a quiet ensemble. 

Is this even possible? When looking at acoustic basses, if a loud instrument is important, what should we look for? What should we stay away from? Or is this a hopeless quest? 

(Note: Unless the advice is specific to a bass, conventional acoustic guitar advice such checking the straightness and relief of the neck, solid top (if affordable), sealed tuning machines, solid top if affordable, etc, can be taken as a given.) 

(Edit: The band currently uses instruments like harp guitar, mandolins, regular acoustic guitars, congas and hand percussion.)