3aAA5. Sound radiation from boxes with tone holes.

Session: Wednesday Morning, May 15

Time: 9:30

Author: Gabriel Weinreich
Location: Dept. of Phys., Univ. of Michigan, Ann Arbor, MI 48109-1120


The normal modes of a hollow box with one or more sound holes, such as forms the radiating element of a typical string instrument, are combinations of ``wood modes'' and ``air modes.'' Wood modes have an average frequency spacing independent of frequency, whereas the average spacing of air modes is inversely proportional to frequency for frequencies low enough to make the ``thin'' dimension of the box smaller than half a wavelength, becoming inversely proportional to the square of the frequency for frequencies above that. As a result, the density of modes of, say, a violin, is generally dominated by wood modes at low frequencies and by air modes at high frequencies. The interplay of the two types of modes has radical consequences for the directivity of string instruments, in that the directional pattern can change drastically within very small musical intervals, perhaps accounting for the special ``flashing brilliance'' that such instruments exhibit. This talk will outline the theory of these effects and support it with experimental observations. [Work supported by NSF.]

from ASA 131st Meeting, Indianapolis, May 1996