Brian Burns early tonewood testing
Posted: Sun Aug 07, 2011 8:20 pm
His conclusions regarding Bearclaw and super tight grain most likely rattled a few builders:
Notes on Stiffness, Density and Q Testing of Tonewoods ~ Brian Burns
Healdsburg Guitar Festival ~August 1997
The reason for doing these tests is to gather some actual measurable data on guitar making woods that might help in judging their quality, and help in deciding how to thin and brace particular tops and backs. At this point I have tested 110 tops, 18 backs, 17 bridges, and miscellaneous billets of rosewood, redwood and spruce. I am about halfway through building a batch of 8 instruments (6 flamencos 2 classics} using wood selected with the
data from these tests as a guide. What properties make the "best" wood is still very much an open question. I have chosen the tops and backs with the highest overall stiffness to density ratios, and highest QE/D ratings. I build Flamenco and classical guitars "in the Spanish style", and I'm looking for woods that will produce that particularly bright tone.
How well this wood testing predicts the tone of finished guitars will certainly not be decided by these eight instruments, but it's a start.
In good journalistic style, conclusions first~
1. Stiffness in guitar soundboard materials (modulus of elasticity) varies much more widely than I thought it would. In a batch of 70 ungraded European Spruce tops, some were almost twice as stiff parallel to the grain as others. Perpendicular to the grain, some were
three times as stiff as others!
2. There is no correlation between parallel and perpendicular stiffness. A top can be stiff with the grain and flexible across the grain, or vice versa. Spruce is always much stiffer parallel to the grain than perpendicular. This batch averaged 17 times as stiff, with one top 9 times stiffer parallel to the grain, and one 29 times stiffer parallel to the grain.
3. Hazeling, from the German, Hazelfichte, or "bear claws", a cross grain figure in some tops,
tends to decrease stiffness parallel to the grain, and increase it perpendicular to the grain. In
heavily figured tops, parallel stiffness decreased up to 17%, and perpendicular stiffness
increased up to 7%. The usual effect is some loss of stiffness overall.
4. Finer grained tops tended to be stiffer parallel to the grain (23% at max.), but extremely fine grained ones tend to fall back to a lower value of parallel stiffness. Grain spacing had no effect on stiffness perpendicular to the grain.
5. In top wood there is some correlation between increased density (specific gravity) and increased stiffness parallel to the grain, but no effect on perpendicular stiffness.
6. In about half of my spruce and redwood tops, the stiffness to density ratio went up markedly in the denser boards. Since the finished weight of a soundboard is dependent on this ratio, roughly half of these denser tops would produce lighter weight finished soundboards than the less dense ones. As they increased in density, they put on "muscle", not fat.
Notes on Stiffness, Density and Q Testing of Tonewoods ~ Brian Burns
Healdsburg Guitar Festival ~August 1997
The reason for doing these tests is to gather some actual measurable data on guitar making woods that might help in judging their quality, and help in deciding how to thin and brace particular tops and backs. At this point I have tested 110 tops, 18 backs, 17 bridges, and miscellaneous billets of rosewood, redwood and spruce. I am about halfway through building a batch of 8 instruments (6 flamencos 2 classics} using wood selected with the
data from these tests as a guide. What properties make the "best" wood is still very much an open question. I have chosen the tops and backs with the highest overall stiffness to density ratios, and highest QE/D ratings. I build Flamenco and classical guitars "in the Spanish style", and I'm looking for woods that will produce that particularly bright tone.
How well this wood testing predicts the tone of finished guitars will certainly not be decided by these eight instruments, but it's a start.
In good journalistic style, conclusions first~
1. Stiffness in guitar soundboard materials (modulus of elasticity) varies much more widely than I thought it would. In a batch of 70 ungraded European Spruce tops, some were almost twice as stiff parallel to the grain as others. Perpendicular to the grain, some were
three times as stiff as others!
2. There is no correlation between parallel and perpendicular stiffness. A top can be stiff with the grain and flexible across the grain, or vice versa. Spruce is always much stiffer parallel to the grain than perpendicular. This batch averaged 17 times as stiff, with one top 9 times stiffer parallel to the grain, and one 29 times stiffer parallel to the grain.
3. Hazeling, from the German, Hazelfichte, or "bear claws", a cross grain figure in some tops,
tends to decrease stiffness parallel to the grain, and increase it perpendicular to the grain. In
heavily figured tops, parallel stiffness decreased up to 17%, and perpendicular stiffness
increased up to 7%. The usual effect is some loss of stiffness overall.
4. Finer grained tops tended to be stiffer parallel to the grain (23% at max.), but extremely fine grained ones tend to fall back to a lower value of parallel stiffness. Grain spacing had no effect on stiffness perpendicular to the grain.
5. In top wood there is some correlation between increased density (specific gravity) and increased stiffness parallel to the grain, but no effect on perpendicular stiffness.
6. In about half of my spruce and redwood tops, the stiffness to density ratio went up markedly in the denser boards. Since the finished weight of a soundboard is dependent on this ratio, roughly half of these denser tops would produce lighter weight finished soundboards than the less dense ones. As they increased in density, they put on "muscle", not fat.