Violin makers miss the best cuts
[This is the pre-edited version of my latest article for Nature’s online news. For more on the subject, I recommend Ulrike Wegst’s article “Wood for Sound” in the American Journal of Botany 93, 1439 (2006).]

Traditional techniques fail to select wood for its sound

Despite their reputation as master craftspeople, violin makers don’t choose the best materials. According to research by a team based in Austria, they tend to pick their wood more for its looks than for its acoustic qualities.

Christoph Buksnowitz of the University of Natural Resources and Applied Life Sciences in Vienna and his coworkers tested wood selected by renowned violin makers (luthiers) to see how beneficial it was to the violin’s sound. They found that the luthiers were generally unable to identify the woods that performed best in laboratory acoustic tests [C. Buksnowitz et al. J. Acoust. Soc. Am. 121, 2384 - 2395 (2007)].

That was admittedly a tall order, since the luthiers had to make their selections just by visual and tactile inspection, without measuring instruments. But this is normal practice in the trade: the instrument-makers tend to depend on rules of thumb and subjective impressions when deciding which pieces of wood to use. “Some violin makers develop their instruments in very high-tech ways, but most seem to go by design criteria optimized over centuries of trial and error”, says materials scientist Ulrike Wegst of the Max Planck Institute for Metals Research in Stuttgart, Germany.

Selecting wood for musical instruments has been made a fine art over the centuries. For a violin, different types of wood are traditionally employed for the different parts of the instrument: ebony and rosewood for the fingerboard, maple for the bridge, and spruce for the soundboard of the body. The latter amplifies the resonance of the strings, and accounts for much of an instrument’s tonal qualities.

Buksnowitz and colleagues selected 84 samples of instrument-quality Norway spruce, one of the favourite woods for violin soundboards. They presented these to 14 top Austrian violin makers in the form of boards measuring 40 by 15 cm. The luthiers were asked to grade the woods according to acoustics, appearance, and overall suitability for making violins.

While the luthiers had to rely on their senses and experience, using traditional techniques such as tapping the woods to assess their sound, the researchers then conducted detailed lab tests of the strength, hardness and acoustic properties.

Comparing the professional and scientific ratings, the researchers found that there was no relation between the gradings of the instrument-makers and the properties that would give the wood a good sound. Even testing the wood’s acoustics by knocking is a poor guide when the wood is still in the form of a plank.

The assessments, they concluded, were being made primarily on visual characteristics such as colour and grain. That’s not as superficial as it might seem; some important properties, such as density, do match with things that can be seen by eye. “Visual qualities can tell us a lot about the performance of a piece of wood”, says Buksnowitz.

He stresses that the inability of violin makers to identify the best wood shouldn’t be seen as a sign of incompetence. “I admire their handiwork and have an honest respect for their skills”, he says. “It is still the talent of the violin maker that creates a master’s violin.”

Indeed, it is a testament to these skills that a luthier can make a first-class instrument from less than perfect wood. They can shape and pare it to meet the customer’s needs, fitting the intrinsic properties of the wood to the taste of the musician. “There are instrument-makers who would say they can build a good instrument from any piece of wood”, Buksnowitz says. “The experienced maker can allow for imperfections in the material and compensate for them”, Wegst agrees.

But Buksnowitz points out that the most highly skilled makers, such as Amati and Stradivari, are not limited by their technique, and so their only hope of making even better instruments is to find better wood.

At the other end of the scale, when violins are mass-produced and little skill enters the process at all, then again the wood could be the determining factor in how good the instrument sounds.

Instrument-makers themselves recognize that there is no general consensus on what is meant by ‘quality’. They agree that they need a more objective way of assessing this, the researchers say. “We want to cooperate with craftsmen to identify the driving factors behind this vague term”, says Buksnowitz.

Wegst agrees that this would be valuable. “As in wine-making, a more systematic approach could make instrument-making more predictable”, she says.