Properties of common tropical hardwoods for fretboard of string instruments

Abstract

AbstractFretboards of string instruments are usually made of rare woods that commonly have a high density, strength, and hardness; further, they are wear resistant, uniform in texture, and feature an elegant color. To reduce the consumption of scarce timber resources, especially of endangered tropical hardwood species, suitable replacement materials should be identified. The substitute can be either common tree species having similar characteristics, or fast-growing plantation wood that has undergone modifications to match the performance of precious woods. This study compares the anatomical structure, physical features, mechanical properties, and surface color of three precious woods traditionally used in fretboards (ebony, Indian rosewood, and African blackwood) against maple, which is used for the backboard, ribs, and necks of string instruments. Based on the data, a set of performance evaluation indices for selecting alternative materials for fretboards is proposed. In specific, the replacement wood should be a diffuse-porous tropical hardwood with few vessels and a smaller diameter, thick fibrous walls, and a cell wall rate of more than 50%. In terms of physical properties, it should have low swelling coefficients for moisture and water absorption, and dimensional stability. The replacement should also display hardness values greater than 9.0 kN in the cross-section and greater than 6.0 kN in the tangential and radial sections. Further, it should have a high modulus of rupture (> 149 MPa) and elasticity (> 14.08 GPa), good impact bending strength, and good wear resistance (80–150 mg/100 r). To satisfy the traditional aesthetics, the wood surface color should be black, dark brown, or dark purple-brown, with colorimetric parameters in the range of 0.0 < L* < 30.0, 0.0 < b* < 6.0, and an a* value as small as possible. The evaluation indicators used for searching potential high-quality alternative tree species are not the same as those for replacing traditional fretboard materials using modified fast-growing plantation wood. The physical and mechanical properties and the surface color of traditional precious fretboard wood are important evaluation indicators for whether the modified fast-growing plantation wood can replace the traditional fretboard wood.