On all acoustic guitars, basses, cellos, violas and violins, the bass bar is a strip of wood (spruce) glued to the back side of the top (front) of the instrument. It is, when facing the front of the instrument, underneath the left foot of the bridge. It provides some structural integrity to the top of the instrument, as the bridge places a fairly heavy strain on the surface when the strings are at full tension. The bass bar's other purpose is to correct for the tuning changes created in the instrument when the F-holes are cut. While moving or replacing the bass bar remains an incredibly expensive and labor intensive task, it is often the only method of altering the tonality of an instrument after the soundpost.