The effect of Mounted Ribs on the Radiation of a Soundboard

TL;DR

This study investigates how mounted ribs on a soundboard influence sound radiation, revealing significant spectral changes and providing a new understanding of structural effects on instrument acoustics using innovative measurement techniques.

Contribution

It demonstrates the impact of ribs on soundboard radiation spectra through a systematic experimental and theoretical approach, introducing a new perspective on instrument design.

Findings

Ribs cause dramatic changes in the radiated spectrum.

A band structure in sound radiation is observed due to ribs.

The simple coupled oscillator model qualitatively explains the spectral effects.

Abstract

The grand piano is one of the most important instruments in western music. Its functioning and details are investigated and understood to a reasonable level, however, differences between manufacturers exist which are hard to explain. To add a new piece of understanding, we decided to investigate the effect of ribs mounted on a soundboard. Apart from pianos, this is important to a wider class of instruments which radiate from a structured surface. From scattering theory, it is well-known that a regular array of scatterers yields a band structure. By a systematic study of the latter, the effect of the ribs on the radiated spectrum is demonstrated for a specially manufactured multichord mimicking topologically a piano soundboard. To distinguish between radiated sound and sound propagated inside the board we use piezopolymers, an innovative, non-invasive technique. As a result we find a dramatic change in the spectrum allowed to propagate in the soundboard which is consequently radiated. An explanation by a simple model of coupled oscillators is given with a very nice qualitative coincidence.