A row of tuned bottles you can blow across or strike. Pour water in and the blown note RISES while the struck note FALLS — the same object, two oscillators, opposite signs. Every frequency is computed from the acoustics (Helmholtz for the air in the neck, a mass-loaded glass shell mode for the tap) and checked against two simulations that were never given the closed form. Pure client-side: no account, no network, no audio files. Credits: Helmholtz; Rayleigh (Theory of Sound) for the ring and the end-correction bounds; Norris & Sheng 1989 for the exact flanged end correction; Levine & Schwinger 1948 for the unflanged; Jundt et al., JASA 119 (2006) for the liquid added-mass law; ISO 16.

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