How the shape of the musical triangle influences its sound

Musical triangles, known for their triangular shape with one open end, have fascinated people with their twinkling sound. However, the acoustic factors behind the triangular shape remain unexplained. We discovered that their triangular shape induces a phenomenon conducive to sustained sound. We measured two-dimensional sound fields around musical triangles using an acousto-optic imaging method. Through our analysis, we found that acoustic resonance occurs in the area of semi-open triangular air created by the musical triangle. Consequently, the resonance produces a louder and longer sound. We believe that the resonances are the acoustical reason for the triangular shape.