The bassbar is a spruce brace fitted and glued on the inside of the top on the bass side. It was not uncommon for many Saxon violins, like this Friedrich August Glass, to have bassbars that were simply carved out of the original wood of the top. They are called integral bassbars, and they greatly inhibit the sound of a violin. Since this instrument is relatively well-made, it’s beneficial to remove the original bar and replace it with a proper fitted bassbar. In professional level instruments, bassbars are often replaced every 25 to 50 years.
First the old bar is cut out and the area where it was is smoothed out. If a normal fitted bassbar is being replaced on a high level instrument great pains are taken not to remove any original wood from the top; however, on a heavy commercial instrument a good deal of wood is removed. The new bar is made from a piece of spruce roughly 5.5mm thick, 270mm long and 20mm high.
After the bar is rough fit, the top is placed in a bassbar fitting jig with alignment bars to register the position of the bassbar as it is more accurately fit using chalk.
When the bar fits, it is glued in place with hot hide glue and allowed to dry overnight.
The bar is shaped to its final dimensions determined by flexibility and tap tones. On the right is the bassbar as it is viewed when looking through the endpin hole.