Pluck a violin string, and it rings. Draw a bow across the string, and a distinctively different, rich, sweet sound fills the air. But how does rosin-dusted horsehair, sticking and slipping as it passes over a metal or gut string, create these sounds? Although a few researchers ahve studied this question during the past century, what happens when a violin string is bowed is still mysterious. Now, physicist Gabriel Weinreich of the University of Michigan in Ann Arbor and French researcher Rene Causse are using a computer as a “digital bow” to study the vibrations that a violin bow produces in a string. In their experiment at a center in Paris for the scientific study of music, the researchers are simulating the way oscillations build up in a string because of a bow’s ability to respond instantaneously to the strings’s motion. “We are dealing with a feedback system that is purposely unstable,” says Weinreich.
As a long wire vibrates back and forth, a sensor measures its velocity about 32,000 times every second. These data go to a computer, which looks up the postulated frictional force that a bow would apply to a string moving at each particular speed. The force is translated into an electric current that is sent through the wire. A small magnet at the wire’s bowing point converts this current into a force on the wire, which then moves, and the process repeats itself. By changing the tables stored in the computer, Weinreich and Causse can test different theories about the role friction plays in the interaction between a violin bow and a string.
“I’m now getting a much better insight into what the old theories predicted,” says Weinreich. “I hope to go beyond that soon.”