Bass strings are wire-wrapped to avoid the fourth-power inharmonicity of thicker cores

Evidence

It can be seen that inharmonicity increases as the square of the component mode (n2) and as the fourth power of the string radius (r4), and that it decreases with increased tension and as the square of increased length. Inharmonicity can be kept low if the strings are thin (small r), long (large L) and under high tension (high T). The effect would therefore be particularly marked for bass strings if they were simply made thicker (larger r) to give them greater mass, since the variation is to the fourth power of r. Therefore, in many stringed instruments, including pianos, guitars and violins, the bass strings are wrapped with wire to increase their mass without increasing the underlying core string’s radius (r). — David M. Howard, Jamie Angus, Acoustics and Psychoacoustics, 1095

Categorization

• CANDY: A clean, explainable fact: why bass strings have wire wrapped around them — great bar trivia about instrument design physics.
• SHARE: Send to a pianist or guitar player who would appreciate why the low strings look wound.