Wood for guitars II : How the material properties of a spruce guitar top influence the tonal quality of the guitar

Abstract

Pacific Rim Tonewoods is the world’s largest supplier of spruce tonewood for the soundboard and bracing of the acoustic guitar. A previous study from our research group (JASA 2019) has demonstrated the importance of (1) longitudinal Young’s Modulus and (2) density of the spruce soundboard on the tonal quality of steel string guitars. This study used pairwise comparisons of listener preference to rank a particular guitar model (the Taylor 814ce). The present study updates this previous work, adding a third material property: internal friction (damping) of the soundboard, as measured by the logarithmic decrement of the resonating spruce billet. In addition, objective data on tonal quality were measured on guitars recorded in an anechoic chamber at the Technical University of Dresden, Germany. Spectral sequence analysis, transfer function, and tone decay were measured, and are correlated with the perceptual data. With these data, we can demonstrate the relative importance of the three material properties on the “performance factors” of guitar quality, such as volume, responsiveness, timbre, attack, and sustain. In doing so, we hope to provide the lutherie community with a predictable means of integrating tonewood material properties into their designs, in order to consistently produce their desired tonal outcomes.