Laura M. Nickerson and Thomas D. Rossing, Rossing@physics.niu.edu
Physics Department
Northern Illinois University
DeKalb, IL 60115
Popular version of paper 4pAA2
Presented Thursday afternoon, November 4, 1999
138th ASA Meeting, Columbus, Ohio
Bronze drums are important to the culture of the Karen people, who live mainly in Burma and the mountainous region between Burma and Thailand. A Karen bronze drum, which is cast in one piece except for the animal adornments, consists of an overlapping tympanum that may range from nine to thirty inches in diameter and a cylinder that is slightly longer than the diameter. Bronze drums have a wide variety of ritual use, both musical and non-musical.
The sound spectrum of a drum shows a dense collection of partials out to about 3 kHz. The corresponding modes of vibration, recorded using electronic TV holography, sometimes show the strongest vibration in the tympanum (as in the upper row in the accompanying figure) and sometimes in the cylindrical shell (as in the bottom row). In all modes, the entire drum vibrates and radiates sound. So far as we know, this is the first time that the acoustical properties of these unusual instruments has been studied.
The tympanum can be modeled as a circular plate, having either a clamped edge or a simply-supported (hinged) edge. The tympanum mode frequencies are in better agreement with those calculated for a flat brass plate with a simply-supported edge than for a plate with a clamped edge. The observed mode frequencies are somewhat less than the calculated frequencies, however, partly due to the mass of the overhanging portion.
The bronze drum is one of the oldest continuous art traditions in Southeast Asia. The first bronze drums have been dated to the sixth century B.C. and were found in northern Vietnam. Karen bronze drums date back at least to the sixteenth century, but they are believed to have had such drums long before this time. Karen people in Burma are a distinct minority ethnic group, and the separate Karen tribes do not necessarily speak the same languages or have the same customs. They most likely did not construct their own drums, but had the Shan craftsmen of eastern Burma create the drums for them.
Bronze drums were very important to the Karen people and to the Karen culture. The owner of a drum richly decorated with frogs was said to be more important to the community than if he owned seven elephants. Ownership of a frog drum was a sign of wealth and status in the Karen community, and village wars and raids occurred over the theft of one or more drums.