Finite-Difference model of mode shape changes of the Myanmar pat wain drum circle using tuning paste

Abstract

The pat wain, a unique drum circle found in Myanmar is investigated in terms of its tuning. The 21 drums are pitched, where tuning is achieved by adding a paste to the drum heads. Additionally, as percussion instruments do not have a perfect harmonic overtone structure, the drums need to be tuned within their spectrum. Using a Finite-Difference model of the drum it is shown that the pitches of the drum decreases with additional mass on the drum head. Still also the overtone structure of the sound changes relative to the fundamental frequency, where applying paste at about half of the drum radius leads to a best fit of the second and third harmonic towards frequency relations of 2:1 and 3:1 respectively. The drum head has a strong internal damping, leading to a very fast decay of the overtones. Still the fundamental decays slowly due to tuning the drum back head to the same frequency as the front membrane. The second and third partials are prolonged as they fit within eigenmodes of the drum air volume. The strong damping, enhanced by the paste, does not change the pitches considerably, which is shown using a viscoelastic Finite-Difference Time Domain model.