The heart of sound The surface of this flat bridge is calculated so that the string, when made to vibrate, will generate a set of harmonious sounds with extended resonance. Results obtained will widely vary depending on the curvature of the surface, the tension, the thickness of the string and the material the latter is made of. Musicological treatises of medieval India meticulously describe this type of bridge termed patrika. In those days, it was made of a metallic plate whose curvature was compared to that of the shell of a tortoise. This plate was propped by a hollow piece of wood (kakubha) and fitted to the lower end of the tube. This essential feature of the instrument does indeed play a key role due to the complex acoustic properties that give this instrument its inimitable voice.