The Physical Mechanism and Influencing Factors of Piano Tone Formation (Part 2)

Feb. 15th,2026  Mr. Huscher

Acoustic Properties of Strings
Strings are the source of timbre, and their physical parameters determine the structure (consonance) of the harmonic series.

Inharmonicity due to Stiffness:

Piano strings (especially steel wire) possess bending stiffness. This causes the overtone frequencies to be slightly higher than the ideal integer multiples (e.g., the 2nd overtone is slightly higher than twice the fundamental frequency). This "inharmonicity" gives the piano its unique sonic character. The greater the stiffness (shorter and thicker the string), the stronger the inharmonicity, resulting in a more metallic or "twangy" sound. At the very beginning of piano design, the string scale is determined first. This involves establishing the inharmonicity for the bass, midrange, and treble strings, thereby defining the piano's "innate" timbre.

String Design Parameters (Scaling):

Length and Tension: Long, thin strings under high tension have less stiffness influence, making their overtones closer to pure harmonics and the timbre purer. This is the primary reason concert grand pianos have a superior tone compared to small upright pianos.

Wrapped Strings: To achieve low frequencies with limited string lengths in the bass register, copper wire is wrapped around a steel core. This increases the mass while maintaining relatively low stiffness, improving the timbre.

Unison Tuning and Detuning:

In the mid and high registers, each note consists of 2 or 3 strings tuned to the same pitch. If these strings are tuned with absolute precision, the sound decays very quickly. If they are slightly detuned, it creates a "double decay" phenomenon and beats, making the sound appear more "singing" and prolonging the sustain.

Longitudinal Vibration:

In addition to transverse vibrations, the longitudinal vibration of the strings also generates high-frequency components (often appearing as "phantom partials" in bass strings), influencing the color of the timbre.