Tension estimation of a kotsuzumi membrane using contact pressure and vibration mode analysis

The kotsuzumi is a Japanese membranophone consisting of two ring-shaped frames with membranes connected by a body. When the cords are gripped, the membranes are pressed against the body, applying tension to the membranes. To enable real-time tension estimation, we propose the Tension from Contact Pressure Method (TCPM). Plastic models were used to simulate membranes and frames for the experiment. Six pressure sensors were placed on a resin body. Tension was varied using weights (0.25–1 kg) attached to the frame. We measured the sound spectrum and pressure when a ball was dropped on the membrane. Tension was calculated from the fundamental vibration frequency, F0. Regarding the experimental results on tension and pressure, the tension increased linearly up to 14 kPa and saturated at 250 N/m above that level. A formula relating pressure and tension was derived. The TCPM was evaluated with an inexperienced subject. F0 and the calculated tension were 290 Hz and 276 N/m, respectively. The F0 of the professional player's sound was 280 Hz, suggesting the subject’s grip was appropriate. The measured pressure and estimated tension were 12 kPa and 230 N/m, respectively. The theoretical and estimated tensions were almost the same, indicating TCPM's potential for tension measurement.