Bass bar
The bass bar, which is glued to the inside of the belly off-center and lengthwise, has important mechanical and acoustical functions. It reinforces the belly and transfers vibrations directly from the bridge down the length of the belly. The shape and fit of the bass bar must correspond to the thickness and arch of the belly and must also be able to accommodate the pressure of the bridge on the belly. The gut strings in use in earlier times had a lower tension, so the belly was subjected to a lower pressure than it is with the string materials commonly in use today. To accommodate the higher pressure, the original bass bars were generally replaced by longer, more massive bass bars during the 19th century.
