Railsback curve shape follows bass and treble string construction limits

Evidence

The overall shape of the curve can be understood from the choice of strings. The bass strings are heavy, to make them low enough in frequency without making the instrument huge. They are wirewound—that is, made heavier by wrapping wire in a spiral fashion around the central wire core. This makes them heavy but reduces inharmonicity. They still have stretched partials, however, causing the Railsback curve to rise sharply at first. The middle strings are still quite long but not so thick and suffer the least inharmonicity. The Railsback curve is relatively flat in the middle region. Last, the treble strings need to be short to make them high frequency without huge tension, leading to greater curvatures and greater inharmonicity—thus the Railsback curve increases its slope again at the high-frequency end. — Eric J. Heller, Why You Hear What You Hear- An…, 1827

Categorization

• SHARE: For anyone who owns a piano or is a pianist: the U-shape of tuning stretch is literally dictated by why strings are thick in bass and short in treble.