Wood grain alignment steers bending waves because trees resist wind

Evidence

The wood is quarter-sawn (cut along the radius) spruce for the top, with the grain along the axis of the instrument, and quarter-sawn maple for the back. A finished back might be 4.5 mm thick at the center, decreasing to 2.5 mm at the edges. The top is more uniform, about 3 mm thick. The front and back plates could be one piece or two pieces cut and reglued. The gluing and the grain alignment are important, since the speed of bending waves is much higher along the grain than perpendicular to it. This is a result of the strength requirements of the tree from which the wood came: wind bends the tree along the vertical grain, and the tree must be stiff and strong against this. — Eric J. Heller, Why You Hear What You Hear- An…, 1741

Categorization

• XREF: Bridging materials science and acoustics; connects to earlier chapters on bending waves and anisotropic propagation.