A soundbox (10) for a musical instrument including a panel (14) having an interior surface (22), two longitudinal edges (16) extending along the periphery of the panel (14), and upper (18) and lower (20) edges lateral to the longitudinal edges (16). The panel (14) also includes a plurality of longitudinal grooves (30 and 31) formed on the interior surface (22) of the panel (14) and of a depth extending along edges (16) and extending through a majority of the thickness of the panel (14). The panel (14) is foldable about the longitudinal grooves (30 and 31) to define a three-dimensional rectilinear shape forming the soundbox (10). A cap (52) is positioned at the upper edge (18) and a base (54) is positioned at the lower edge (20), and truss rods (64A and 64B) extend between the cap and base to assemble the components and increase the strength of the soundbox.