Eigendrum solves the eigenvalue problem −∇²u = λu numerically by meshing shapes with triangles and computing the smallest eigenvalues of Kφ = λMφ. The solver is validated against exact solutions: circle frequencies via Bessel functions and rectangle frequencies as π²(m²/a² + n²/b²), reproducing results to better than 0.1%. Striking different spots excites different mode mixtures—hitting a node prevents that mode from sounding.

Users can draw shapes or enter parametric equations like 1 + 0.3cos(5t) for complex forms. The tool addresses Mark Kac's 1966 question: two different shapes (Kac drum I and II) with identical spectra prove you cannot hear the shape of a drum. Absolute pitch depends on size/tension (sliders), while damping follows Rayleigh model where high overtones fade first.

Hosted at eigendrum.com, it runs entirely client-side with no installation required.