| Popis: |
Frequency‐response curves of violins are obtained by a modification of a method described by Backhaus and Weymann. A phosphor‐bronze wire, properly damped to prevent the formation of standing waves, is substituted for one of the violin strings. Vibrations of the wire very near the violin bridge are produced by the interaction of a transverse magnetic field and an alternating current in the wire. The violin body responds at the frequency of the alternating current, variable from 30 to 20,000 cycles per second. The resulting sound is received by a microphone, whose output is amplified and automatically recorded by an audiograph on a logarithmic pressure versus frequency scale. This avoids the inconveniences of a previous method using harmonic analyses of steady tones produced by hand bowing. The similarity of frequency‐response curves for old and new violins raises doubts as to the significance of the steady‐tone results, and leads to a study of transient effects. The earlier attempts to study transients involved hand bowing, and failed because of the complexity of the tone. Pure‐tone excitation, used to obtain growths and decays, allows the determination and comparison of the damping constants of the violins. The transient measurements are made using a cathode‐ray tube and high speed camera. |
