Idiophone Bar Shape Optimization Using FEM

Participants: Douglas Beaton and Gary Scavone

Period: 2019 - ongoing


The bars of marimbas, vibraphones, xylophones and other similar instruments are tuned by carving an “undercut” or “cutaway” on a bar’s bottom surface. For lower notes on an instrument, it is common practice to tune three vertical bending modes such that their frequencies form harmonic relationships. Other modes, such as torsional and lateral flexural modes are typically left untuned. Makers have complained of untuned modes polluting bar timbre. For marimbas, such problems appear over a specific range in the keyboard and can result in valuable rosewood condemned to the reject bin.

This project investigates idiophone bar modal behaviour, both computationally and experimentally. Finite element models of marimba and vibraphone bars have been developed to tune modal frequencies. Experimental modal analysis measurements have been performed on rosewood and synthetic marimba bars. Work exploring shape optimization, sound synthesis and new material options is ongoing.