Acoustics of the Mridangam: Study of a New Design of a South Indian Drum

Abstract

The mridangam is the primary musical drum of South India and is comprised of three primary parts: the tonal head, bass head, and central wooden shell to which the two heads are traditionally fastened by leather thongs. In this study, the acoustical properties of the mridangam were studied with the traditional mounting system as well as a new mounting system that has been developed as a convenient and user-friendly method of fastening the heads. Measurements of modes and mode frequencies were made by mechanically exciting the heads with a mechanical vibrator and laser vibrometer setup. Drumhead vibration and sound spectra from standard strokes on both heads were also recorded. Based on the sound spectra and response curves, the new mounting system seems to maintain the important spectral features of the traditional design, including the nearly harmonic relationship of the first five modes. This is of practical interest since the new mounting system does not change the basic tonality of the instrument. Using a similar analysis, the following conclusions were drawn from measurements of other practical performance variables: 1) Altering the pitch of the tonal head by an interval of a fifth with the new mounting system did not change the basic acoustical properties of the drumhead. 2) Wetting the bass head caused a decrease in bass head frequencies and an overall damping effect, but did not change the other spectral features of the bass or tonal heads. 3) Insertion of an iron oxide powder into the tonal head did not detectably change the acoustic properties of the tonal head. 4) Comparisons of the traditional wheat paste and silicone rubber on the bass head revealed that the two dampening fixtures generate nearly identical spectra.