Bass bar

A bass bar is a structural component inside the body of a stringed instrument, primarily those in the violin family (violin, viola, cello, double bass). It is a long, thin strip of wood, typically spruce, that is glued to the underside of the top plate (soundboard) of the instrument, running lengthwise, approximately parallel to and just off-center from the center joint.

The primary function of the bass bar is to distribute vibrations from the bridge across the top plate. The bridge, which supports the strings, transmits vibrations from the strings when they are played. The bass bar helps to spread these vibrations evenly across the soundboard, allowing it to resonate and project the sound. It also adds strength and stiffness to the top plate, helping it to withstand the downward pressure exerted by the strings via the bridge. Without a bass bar, the top plate would be more susceptible to cracking and would produce a weaker, less complex sound.

The size, shape, and placement of the bass bar significantly influence the tonal characteristics of the instrument. Luthiers carefully carve and fit the bass bar to optimize the instrument's sound. Factors such as the bar's length, height, curvature, and density all affect the instrument's response and timbre. Experimentation and subtle adjustments to the bass bar are common during the instrument-making process.

While its primary function is structural and acoustic, the bass bar also plays a crucial role in the instrument's longevity. By distributing the string tension, it prevents the top plate from collapsing over time.