bComputational acoustic modeling laboratory, CIRMMT, McGill University
A marimba barís modal behaviour is governed by the shape of its Ďundercutí. 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.
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