Why Are Violin Sound Holes Shaped That Way?

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Although people sometimes use the word "evolution" when it comes to technology — the typewriter "evolved" into the keyboard on your smartphone screen, for instance — they generally mean it as a metaphor. There are no mutations in innovations, no natural selection helping a device make more versions of itself. But according to MIT researchers, the way the modern violin's sound holes came to be is nothing short of technological evolution. They didn't come about by design, but by generations of design accidents.

Lute Me Ask You A Question

By day, Nicholas Makris is a professor of mechanical and ocean engineering at MIT. But on weekends, he plays the lute. Compared to a violin, the lute is a simple instrument: it's got a rounded form like a pear cut in half with a circular sound hole called a rosette, which is elaborately carved out of smaller shapes.

One day, another lute player asked the scientist-musician Makris whether those elaborate carvings make any difference to the instrument's sound. Curious, Makris worked with MIT researcher Yuming Liu to model airflow through two different holes, one round, the other elaborate. In both shapes, they found that air flowed fastest near the edges. It didn't matter if the hole was open like a guitar's or partially filled like a lute's; the air in the center of the full shape still moved more slowly than the air near the edges. The faster the air moves, the more powerful the sound.

The musician's question kicked off a seven-year project that culminated in a paper published in the Proceedings of the Royal Society A.

After recruiting a team of fellow MIT researchers and the violinmaker Roman Barnas, Makris looked at ancestors of the modern violin over 800 years from the 18th century all the way back to the 10th-century "fithele," the simple bowed instrument whose name gave rise to the word "fiddle."

They found that the shape of the sound holes appeared to have evolved over the centuries, from simple circles to half-moons to decorative "C" shapes all the way to the "f-holes" that violins and other bowed instruments bear today. That increase in frills and flourishes created a bigger edge-to-center ratio, which led to a more and more sonic power until the sound amplified by the 18th-century violin's f-holes was roughly double that of the 10th-century round holes. But we know that because of modern technology. How did luthiers hit upon these shapes hundreds of years ago?

Evolution of the violin's sound hole.

F Stands For Flawless

To answer that question, the team gathered the measurements from hundreds of 17th- and 18th-century violins — the era that saw c-shaped holes turn into f-shaped holes — to create an evolutionary model. The differences from instrument to instrument were so small, they concluded, that they could reasonably be explained by human error. To put it another way, just as mutations in DNA sometimes give rise to useful traits, errors in craftsmanship sometimes give rise to more powerful-sounding instruments.

"We found that if you try to replicate a sound hole exactly from the last one you made, you'll always have a little error," Makris said in a press release. "You're cutting with a knife into thin wood and you can't get it perfectly, and the error we report is about 2 percent ... always within what would have happened if it was an evolutionary change, accidentally from random fluctuations."

If a luthier made an instrument that sounded better than the others, they'd probably try to repeat what they did the next time around. These changes would be small from instrument to instrument, but over the centuries, it could turn a circle into a c-shaped hole and a c-shaped hole into an f-shaped hole. But even more amazingly, intentional attempts in the 19th century to improve upon the f-hole design fell flat, making the sound worse instead of better. The technological evolution of the violin's sound hole seems to have created the optimal shape for the job.

Acoustic analysis of different sound-hole shapes.

Bonus fact: If f-holes are so perfect, why have guitars mostly kept the single round hole? The answer to this is complex enough for its own article, but in essence, guitars didn't have the "evolutionary pressure" to be powerful that violins did. While the Renaissance brought orchestras that made violins (and their bowed brethren) compete with other instruments in volume, guitars remained mostly solo and small-group instruments. That is, until the turn of the 20th century, when dance bands made guitarists compete with full horn sections. That was when Orville Gibson invented the archtop guitar, which features — you guessed it — f-holes. Guitarists still use archtops when they need to project sound a good distance, but the classic flat-top guitar with the round hole is still preferred for many types of music because of its characteristic tone.

For more about the science of music, check out "This Is Your Brain on Music: The Science of a Human Obsession" by Daniel J. Levitin. We handpick reading recommendations we think you may like. If you choose to make a purchase through that link, Curiosity will get a share of the sale.

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Written by Ashley Hamer December 19, 2017