The other indication of a bass bar that needs replacing is a bulging of the arch of the top, at the upper curve of the bass f-hole. The areas of the top at the upper and lower arcs of the f-hole are known as the hinges, for they are where most of the movement of the top takes place. The top is left extra thick in these areas with this in mind. While they re supposed to move, it s the bass bar that keeps the movement from deforming the top on the bass side. If the arch has bulged at the upper arc, the bar is not providing enough support for the top to return to its natural shape as it flexes.
Cracks can develop along the bass bar from accidents, a poorly fit bar, or a weak top.
They create another problem entirely, for the repair of a bass bar crack is a major undertaking. It requires removing the top, taking out the old bar, and then fitting a new one over reinforcements. As for that perennial worry about the bass bar relax. In more than 20 years of buzz-hunting, I ve never found the bass bar to be the cause. The finished bassbar, shaped and sanded.