inharmoniska

Inharmoniska is a term used in acoustics to describe components of a sound that do not form a harmonic series with the sound’s fundamental frequency. In practice, it refers to partials whose frequencies deviate from integer multiples of the fundamental, resulting in a less strictly harmonic spectrum.

The phenomenon is rooted in physical properties of real instruments. Material stiffness, geometry, and boundary conditions cause overtones to diverge from exact multiples of the fundamental. For example, piano strings are relatively stiff, producing higher partials that are sharper than the harmonic series; bells, metal pipes, and other percussion instruments often exhibit pronounced inharmonicity.

Perceptually, inharmoniska influences timbre and tuning. Increased inharmonicity can make a note sound brighter or more metallic and can introduce beating between partials. Instrument builders and tuners address this effect: pianos are often tuned with stretching to compensate for inharmonicity, while other instruments are designed to minimize or exploit it for a desired sound character.

Measurement and modeling commonly use an inharmonicity coefficient, denoted by B, to describe how partial frequencies diverge as the harmonic index increases. A simplified model expresses the nth partial as approximately n times the fundamental frequency, multiplied by a factor that increases with B and n.

Applications of the concept appear in instrument design, acoustical analysis, and digital sound synthesis. It also informs musicology and the study of how real-world sounds differ from ideal harmonic models. See also harmonic series and inharmonicity.