On the selection of wood and bamboo for musical instruments
As promised, I’m providing a summary of a very interesting article that I ran across while discussing materials for bowmaking:Ulrik G.K. Wegst, Annu. Rev. Mater. Res, 2008, 38:323-49
• Several Ashbe plots were generated from the Natural Materials Selector (now Ansys Granta), showing correlations between characteristic properties for wood and bamboo species, as grouped into distinct material classes for different musical instruments. Beneficial trends could be identified based on known instrument performance traits.
• Bamboo has comparable Young’s modulus and density to traditional bowmaking woods, and the ratio of the properties is also similar but with bamboo skewed toward higher specific modulus - as with the best Pernambuco. (Swartzia is the “alternative” bowmaking wood closest to Paubrasilia.) High specific modulus is proportional to the speed of sound within the materials, which is measurable by the Lucchi meter. Meanwhile, CFRP has a dramatically higher specific modulus while also being denser than even the densest wood species.
• Denser woods do not efficiently radiate sound to the environment because of their strong impedance mismatch with air. (This is also true for CFRP.) The lack of radiative loss means that more energy can be transmitted between bow and string.
• The sound radiation coefficient of a soundboard (i.e., top plate) depends very strongly on density, with less-dense boards radiating more on average across all audible frequencies.
• The peak amplitude of a soundboard depends on the ratio of the sound radiation coefficient to the loss coefficient (i.e., internal damping). Soundboards made from spruce and related coniferous timbers typically have low loss coefficients, being both light and stiff.
• The maple and similar hardwoods used for constructing viol backs and ribs provide moderate sound radiation and characteristic impedance. This assists in reflecting a viol’s internal sound out through the f-holes.
• Compared to maple, bamboo has a higher sound radiation coefficient, lower impedance, and reduced loss coefficient.
• Compared to spruce and related softwoods, bamboo has a lower sound radiation coefficient and higher impedance. Thus, it is more suitable for bridges and support structures than for soundboards.
• Environmental aging (e.g., through slow roasting) enhances dimensional stability, deepens color, and actually improves the transverse toughness of bamboo. This is analogous to torrefaction in wood, except the latter does not enhance resistance to splitting.
• Seasoning for bamboo musical instruments is generally much less than a decade and typically only two years.
• Bamboo fiber has a much higher specific stiffness than nylon or gut while being very strong. Thus, it is an interesting candidate for producing instrument strings!
From the conclusions: “Bamboo is the only material worldwide with a mechanical and acoustical property profile that simultaneously satisfies all design criteria and functional requirements of all classes of musical instruments; even strings can be made from it.”
My takeaway? Bamboo is great stuff and should be studied for optimal performance in different musical contexts.
Replies (1)
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Bamboo has a tentendy to crack. In this respect it is much worse than hardwoods. Bamboo instrumrunts are frequently reimforced to try to prevent cracks, but even that does not solve the issue.
When bamboo is dried it becomes very stiff (and prone to cracking) I believe it may be too stiff for uses such as bows.
There are physical issues with bamboo. There are nodes (rings) in it which have different properties. You cannot get a particularly long piece without them. Bamboo is not as thick as traditiinal trees, and it is hallow. You cannot get wide cuts of it.
It may be that my assessment is wrong. But my impression is that bamboo is unsuitable.