Savart Journal

The Effect of Finishes on the Vibration Properties of Spruce Guitar Soundboard Wood

Howard Page Stephens

Abstract

This paper presents a study of the effect of a sealer and four finishes on the vibration properties of spruce for guitar soundboards. Two of the finishes, de-waxed shellac and nitrocellulose instrument lacquer, are evaporative finishes, traditionally used for guitars. The third and fourth are reactive shellac-based finishes. The study measured the fundamental vibrational frequency, f₀, and damping quality factor, Q, of Sitka spruce test bars machined in along-grain and cross-grain orientations, and coated with sealer and the finishes. The sealer alone produced significant changes in both f₀ and Q for the two grain orientations: the along-grain f0 decreased; the cross-grain f₀ increased, and Q for both grain orientations decreased. The finish top coats affected f₀ for only the along-grain bars, which decreased with top coat application. Compared to Q for the sealer coating, all of the top coats cured for seven weeks increased Q for the along-grain bars, but did not affect Q for the cross-grain bars. Statistical analyses showed that all of the top coat finishes cured for seven weeks were equivalent with respect to their effect on the vibrational properties of the spruce bars.

Article Information

Article published Nov 7, 2015.
This article has been accessed 8390 times since publication.

The Savart Journal is published in collaboration with the Guild of American Luthiers.

Howard Page Stephens
Sandia National Laboratories (Retired)
United States

After receiving his PhD from Purdue University, where he was a National Science Foundation Fellow, Howard joined Sandia National Laboratories, pursuing a career in materials research and R&D management. He also served as a Division Chair of the American Chemical Society and as a Technical Advisor to the U.S. Department of Energy, Office of Basic Energy Sciences. After retiring from Sandia, Howard returned to his interest in lutherie, applying his scientific experience to researching plate vibrational properties. He is a member of the Guild of American Luthiers.