Acoustical characterization of woods for guitars

Abstract

The top and back plates of a guitar are among its most important components for producing the desired quality of sound from the instrument. Spruce, cedar, and redwood are wood species commonly selected by luthiers for guitar tops. Top woods have very similar acoustical characteristics which set them apart from back woods. Yet there exist subtle differences between these top woods that have interesting musical implications. Likewise back woods, e.g., rosewood, mahogany, and maple, are similar but not identical in acoustical character. Five fundamental properties of these wood plates that hold the key to much of their musical qualities are (1) density, (2) Young's modulus, and (3) low‐frequency damping along‐the‐grain, and (4) Young's modulus and (5) low‐frequency damping across‐the‐grain. Undesirable plate characteristics from the luthier's view, e.g., runout and skewed grain, can be correlated with measurable deviations from the normal values of these properties. A loudness index is proposed which combines the five properties into a single unit to characterize generally the plate's suitability for guitar construction. [Work supported by the National Science Foundation.]