The Violin

Violin and Guitar Bridges

• Guitar bridge
  • Low, flat, hard to move.
  • Only moves up-down
  • Fairly small down-bearing
• Violin bridge
  • Tall, flexible, easy to move
  • Converts side-side motion of
  • String into up-down motion.
  • Large down-bearing.
• The larger downbearing of the violin couples string energy to bridge and so to the body of the violin much more efficiently than does the guitar bridge. Thus the violin is louder than the guitar despite its smaller body and the sound from a plucked string decays much faster.

Stick-Slip Bowing

As the bow is drawn across the string sticktion causes the string to follow the bow. This stretches the string and the force needed to keep pulling the string out of line increases the further the string moves. At some point the frictional force is no longer large enough to hold the string which starts to slip. As soon as it slips the force sharply decreases and the string slips even faster. The string will slip back to the rest position and keep moving, because of its inertia. As the string moves out to the other side of equilibrium it will slow down. Eventually its velocity will be close enough to that of the bow that the frictional force again becomes strong enough to drive the string. The effect is to move the string in the direction of the bow at a fairly steady rate with short period when the string snaps back very rapidly.

The combined effect is to launch little kinks along the string that bounce around the string at a frequency set by the natural frequency of the string. If you touch the string near a nodal position for a higher mode then you can force the string to vibrate ina higher mode. For example, touching the string at its mid-point will produce a pitch an octave above the fundamental with two kinks travelling on the string at any instant.