Post-classification of nominally identical steel-string guitars using bridge admittances

Dynamic and acoustical measurements were conducted on 18 nominally identical acoustic guitars coming off the same production line and post-classified by the manufacturer as either bassy (i.e., with a more prominent bass response), mid-even (i.e., well-rounded and sounding even from string to string) or treble (i.e., with a brighter sound that cuts through the band). One goal was to find features of the guitar admittances that could be used to automatically classify them according to these categories. A second goal was to investigate whether experienced guitarists agreed with the classifications provided by the manufacturer. Physical properties were investigated independently and in conjunction with perceptual assessments by musicians collected during a classification task. Despite very low agreement across guitarists as well as between musicians and the manufacturer, results showed that the bassy guitars had a lower frequency for their breathing mode. This suggests a lower stiffness-to-weight ratio for the respective guitar bodies, which may be caused by small variations in the plate thickness or wood properties. The guitars characterized as treble in this study tended to have lower averaged mobility in the 600–2000 Hz range, which might suggest a weaker string-to-body coupling at those frequencies and/or a longer decay for higher partials, though these characteristics were not confirmed