Coin Pinger
Acoustic bullion authentication — free, private, on-device
Free tool
Coin resonance calculator
Any coin with a published mass and diameter has a computable ring. Enter its specs and metal, and this calculator derives the resonance frequencies a genuine specimen should ping at — the same first-principles free-plate physics behind every reference on this site.
Coin parameters
No thickness needed — the model derives the effective disc thickness from mass and diameter, which is more accurate than a rim caliper reading (the raised rim concentrates metal at the edge).
Expected resonance ranges
| Mode | Expected ring | Recommended variance |
|---|---|---|
| Enter coin parameters above. | ||
Opens the free tester with this reference preselected — audio never leaves your device. The tolerance bands use the same quadrature model as our published references (capture reproducibility, manufacturing spread, per-metal model uncertainty) — see the methodology.
How it works
A struck coin vibrates as a free circular plate. Its lowest audible modes (c0d2, c0d3, c0d4 — two, three, and four nodal diameters) ring at frequencies fixed by geometry and metal: f = (λ²/2πa²)·√(D/ρh) with the Leissa eigenvalues λ², a rim/relief correction, and a thick-plate correction on the higher modes. Modes above 20 kHz are dropped — phone microphones can't read them reliably. Accuracy is limited mainly by the metal's published elastic modulus (roughly ±5% on each center; best for silver). For a specimen-exact reference, calibrate a coin you know is genuine instead.