What is a bass bar and what is it used for?
The bass bar is a long piece of would attached to the soundboard (top plate) inside the violin.
It runs along the G-string of the violin (the bass string).
It is there for several reasons.
It supports the tension of the strings.
In Baroque times player used gut-strings, they produced very little string pressure compared with the type of strings we use today.
Now we use strings that produce more than 80 pounds of string pressure, so bass bars of baroque violins needed to be replaced.
The bass string of the violin resonates mostly on the soundboard, the top plate.
The bass bar enhances this vibration.
The bass bar is glued to the soundboard.