aMcGill University
bComputational acoustic modeling laboratory, CIRMMT, McGill University
Abstract :
A marimba bar’s modal behaviour is governed by the shape of its
‘undercut’. Manufacturers typically shape these undercuts to tune up
to three modes for specified frequencies. With only three or fewer
partials to tune, numerous bar geometries may yield the desired
results. Different manufacturers will employ different techniques to
arrive at suitable bar geometries. This diversity in tuning approaches,
coupled with the natural variability of wood, results in a multitude of
undercut shapes. Two bars may produce the same musical note
despite plainly visible differences in undercut geometry.
This work uses experimental modal analysis to investigate the
variability of marimba bar modal behaviour. Measurements are
performed on numerous bars of the same note. Geometric data,
including overall dimensions and mass, are recorded for each bar.
Several manufacturers are represented in the resulting data set,
including Yamaha, Musser and Marimba One.
Variability of the tuned and untuned modal frequencies are of primary
interest. Untuned torsional modes may compromise bar performance
if their frequencies are near those of the tuned modes. The proximity
of these untuned mode frequencies to those of the tuned modes is
therefore also investigated. Results are presented comparing bar
performance both between brands and within a brand.