Wood Usage in Musical Instruments

Wood is used in instrument making for both aesthetic reasons - it satisfies the eye and the feel - and more importantly for its contribution to the quality of the sound produced. It is also used because of a lack of an alternative - think didgeridoos.

A basic summary of wood and its characteristics is useful:.

TREES - THE SOURCE

Trees are classified as hardwoods (Angiosperms) or soft woods (Gymnosperms) which refers to their class not their hardness - balsa is technically a hardwood. The cross section of a trunk has an outside layer of sapwood which is where the continued growth of the tree happens. You can think of a tree as having and active outer layer of live wood and an internal scaffolding layer of heartwood which no longer participates in annual growth and exchanges of sap and nutrients.  The core of the trunk is termed heartwood. The tree grows in girth and height by laying down successive sapwood layers which are visible in many species as annual rings, a ring representing a years growth. In addition to rings many species have radial medullary rays which are tissues arranged radially from the centre of the trunk. A piece of wood cut along the ray often exhibits medullary rays in it’s figure. It is termed “fiddleback” and sought after for the body of instruments for both appearance and performance. This cut configuration is termed quarter cut and apart from the possibility of exhibiting rays is much more dimensionally stable during seasoning.      

 Terminology

• Softwoods - Gymnosperms - Over 1000 species in existence
• Hardwoods - Angiosperms - By far the most diverse group of land plants with 64 orders, 416 families, approximately 13,000 known genera and 300,000 known species
• Sapwood - the outer layers of a trunk, typically paler in contrast to heartwood
• Heartwood - the core layers of wood
• Figure - the visual appearance including rays, flamed, crotch
• Growth rings - the usually visible annual growth rings in a trunk cross section. Used in the dating science of dendrochronology
• Medullary Rays - radially located tissues in the log of some species which contributes the term ‘fiddleback’ to all wood users
• Grain - the tactile attribute - e.g coarse, open, smooth
• End grain - the end face of the plank
• Side grain - a side face of the plank
• Flatsawn - milled through & through with often no regard to figure or stability - a commercial reality for yield
• Quartersawn - a piece of wood cut on the quarter of the trunk. In instrument making critical for appearance and tone support.
• Density - 2 measures - Green when tree felled and Air Dry at EMC
• Shrinkage - the change in dimension due to the loss of bound moisture during seasoning - 3 parameters
• Radial Shrinkage - such as the width of a quarter sawn board over seasoning
• Tangential Shrinkage - the shrinkage around the perimeter - often causes splits
• Longitudinal Shrinkage - down the length of a stick - typically negligible
• Air dried - an ideal - wood milled and left to reach EMC over time.
• Kiln Dried - wood which is processed in a kiln to speed the reaching of EMC
• Collapse - internal and often invisible voids in the wood usually due to incompetent kiln drying
• Equilibrium Moisture Content - EMC - wood which has stabilised after air drying to it’s environment
• Reaction wood - wood with internal unrelieved stresses. Use of limb wood an exemplar
• Hardness - measured in Janka and assessed by pressing a ball into the face of the stick
• Modulus of Elasticity - critical if you make handles for striking tools - probably essential to use in acoustic instruments
• Modulus of Rupture - a measure of the ability of wood to carry loads
• Tonewood - huge subject related to species used in woodwind an stringed instruments. Refer to Wikipedia HERE