Measurements of mechanical properties of Adirondack spruce

Abstract

Adirondack spruce (Picea rubens), also known as Eastern red spruce or Appalachian spruce, is a conifer found primarily in New England, the Appalachians and eastern Canada. This wood has been historically used in the production of fancy foods such as spruce beer and spruce gum (from the needles especially), but also as construction lumber, pulpwood and even as Christmas trees. Adirondack spruce wood began to be used in the 19^th century for piano, guitar and mandolin soundboards. Prior to World War II, it was indeed the preferred soundboard tone wood for several guitar makers and is still widely in use for this purpose.

Despite its large use in various fields, Adirondack spruce’s mechanical properties, like Young’s moduli in principal and transverse directions and shear modulus, are not well documented. In this work, several methods are used to evaluate such properties of twelve quarter-cut orthotropic plates selected for guitar soundboards. The considered methods and corresponding frequency ranges includes (1) Dynamical mechanical analysis, which provides values at low frequency (i.e. below 100 Hz), (2) Identification of low-frequency vibration modes between approximately 100 Hz and 500 Hz, (3) Spatial Fourier transform and inhomogeneous wave correlation between 500 Hz and 5000 Hz, and (4) Asymptotic methods up to 10 kHz. The identified values for the elastic constants of this orthotropic material are summarized and compared as a function of frequency.