Instruments crafted from the late 17th century onwards by revered violin maker Antonio Stradivari sell for millions of dollars today, and musicians and scientists have long sought to explain their superb sound quality.
Now, American scientists have come up with a possible explanation: A dramatic European cold spell may have enhanced the quality of wood from which the instruments were crafted.
A sharp dip in temperatures between 1645 and 1715 coincided with a reduction in sunspots and the sun's overall activity known as the Maunder Minimum. Researchers say those factors may have slowed tree growth, thereby creating the ideal building material for violins later manufactured.
The violin first emerged in northern Italy in the mid-1500s. Many of the most distinguished violins ever created were produced by famous local families of violin makers—such as Amati, Guarneri and Stradivari—in the 17th and early 18th centuries. Stradivari was the most famous of these craftsmen, and produced over 1,100 violas, guitars, cellos, and violins. Around 600 of his instruments exist today.
Many top musicians today prefer to play instruments created by Stradivari or his contemporaries. But scientists have found it difficult to pin down the exact difference between a modern violin and a Stradivarius.
"It may be that Stradivarius violins are so well made that they are easier to play" to their best potential, said John Topham a tree ring expert and violin maker in Surrey, England. "The finest instruments are the ones that allow musicians to express themselves best," he said.
Henri Grissino-Mayer, co-author behind the new study and tree ring scientist at the University of Tennessee in Knoxville, said there is continuing debate as to whether these instruments do indeed sound superior and what, if anything, explains that quality other than the legendary skill of their makers.
"There are many competing hypotheses … and a lot of it is grounded in folklore," he said. "Some people even believe [Stradivari] used the wood of ancient castles and cathedrals."
Others suggest that Stradivari and his contemporaries used a special varnish (the secret of which has been lost today), or that the wood was chemically treated, soaked in water, specially dried, or stored for long periods of time.
Grissino-Mayer believes many of these explanations are flawed, however. For example, despite scientific investigations using ultraviolet photography, electron microscopy, and x-rays, a secret varnish has yet to be revealed. Furthermore, tree ring analysis has demonstrated that many surviving Stradivarius violins were made using wood that grew during Stradivari's lifetime, discounting the idea that it may have come from ancient buildings.
Instead, Grissino-Mayer and climatologist Lloyd Burckle of Columbia University in New York have come up with an alternative hypothesis. They suggest that climatic cooling over many decades affected rates of tree growth and may have contributed to the acoustic quality of the violins produced by Stradivari and his contemporaries.
Dense wood with narrow growth rings may help to "instill a superior tone and brilliance in violins," the researchers wrote, adding that wood grown under fast conditions is less resonant and unlikely to survive the stresses placed on a violin.
"Much of Europe was gripped by the little ice age between around 1400 and 1800," said Grissino-Mayer, noting that the period of cold weather and long winters peaked between 1645 and 1715. Trees growing during that peak period, the so-called Maunder Minimum, "showed the slowest growth rates of the entire last 500 years," he said.
Intriguingly, Stradivari was born one year before the start of the Maunder Minimum. He produced violins from 1666 until his death in 1737. Other studies have shown that Stradivari used violins built from spruce wood contemporary to his lifetime, and Grissino-Mayer believes this would have been locally obtained.
Still, scientists like Grissino-Mayer don't discount the unique talents Stradivari and his contemporary artisans brought to producing wonderful-sounding violins. "They didn't only have better materials … the skills of the maker will have a considerable effect on the tonal quality of the final instrument," said Grissino-Mayer.
"It's an interesting idea, but there is little supporting evidence," said Topham, the violin maker and tree ring expert. "They have come up with a theory based on just a few examples [of Stradivari's work], which are not representative of his entire output."
Topham has examined or repaired over 80 Stradivarius violins. He notes that while some of Stradivari's early violins do bear wood with narrow tree rings, others have wider spacing. He also argues that the spacing of tree rings across the range of Stradivarius violins he has examined lack consistency.
Nevertheless, John Montgomery, secretary of the American Federation of Violin and Bow Makers who is based in Raleigh, North Carolina, said of all the so-called secrets of violin production, "the most important element is wood selection." Wood inhibits or favors vibrations depending on its characteristics, said Montgomery, and the wood chosen by early, great instrument makers was excellent.
"The good news is that we continue to find wood with great properties today," he said, adding that well-made new instruments can sound as outstanding as old masters.