Testing a material's acoustics by knocking on it is a poor guide when the wood is still in the form of a plank.Getty

Despite their reputation as master craftspeople, violin makers don't actually 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, Austria, 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 pick out the woods that perform best in laboratory acoustic tests¹.

That was admittedly a tall order, since the luthiers had to make their selections just by visual and tactile inspection, without the use of any tools. But this is normal practice in the trade: instrument-makers tend to rely on traditional rules of thumb and on subjective impressions, rather than on modern measuring devices, 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.

Knock on wood

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

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

Although 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, they report in the Journal of the Acoustical Society of America¹. 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 mainly from 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.

Cut to size

Choosing a good wood is, of course, only a small part of the equation when it comes to building a good musical instrument. "It is still the talent of the violin maker that creates a master's violin," notes Buksnowitz.

The way the wood is cut and shaped makes a huge difference to sound. "There are instrument-makers who would say they can build a good instrument from any piece of wood," Buksnowitz says. Wegst agrees: "The experienced maker can allow for imperfections in the material and compensate for them."

But Buksnowitz points out that the most highly skilled makers, such as Amati and Stradivari, have probably mastered the technique of violin building, so their only hope of making even better instruments is to find better wood.

At the other end of the scale, where violins are mass-produced, then again the wood could be the determining factor in how good the instrument sounds.

Visit our makerscantpickout_go.html">newsblog to read and post comments about this story.  

• References

  1. Buksnowitz C., Teischinger A., Müller U., Pahler A. & Evans R. J. Acoust. Soc. Am., 121 . 2384 - 2395 (2007).