Stradivari’s Secrets

From Science News June 30th, 2007; Vol.171 #26 (p. 414)

From Salt Lake City, at a meeting of the Acoustical Society of America

Antonio Stradivari’s coveted violins have been around for more than 3 centuries, but experts are still struggling to understand just why they sound so magnificent. A new study of the vibrations of 17 violins from various makers finds one Stradivari that’s especially efficient at directing sound toward the audience.

George Bissinger of East Carolina University in Greenville, N.C., used three lasers and the Doppler effect—the familiar phenomenon that makes a siren’s pitch drop when an ambulance speeds by—to image the vibrations of each violin’s surfaces.

The real-time three-dimensional mapping, which Bissinger says is unprecedented, enabled him to distinguish vibrations that move the violin’s surface up and down from those that compress and stretch it. Only the former, called transverse vibrations, move the air and thus produce sound. One of the two Stradivaris tested had the strongest transverse vibrations of any of the violins, Bissinger says.

When he measured sound intensity, that violin also turned out to project a larger proportion of its total sound energy from its front, which usually faces the audience.

Bissinger says that the Strad’s peculiarities could derive from the treatment given to the wood or from the varnish applied to it, both of which are largely unknown.

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