Physics of the Bacon Internal Resonator Banjo
  The internal resonator banjo, patented and first sold by Fred Bacon around 1906, remains something of a cult favorite and is still produced by some independent luthiers. According to enthusiasts, the characteristic design elements produce a sound that is mellower, richer, and of greater complexity and presence than without them. Aspects of that sound are studied here, comparing instruments that are otherwise identical and identifying physics mechanisms that are likely responsible. 
David Politzer
physics.pop-ph