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Silver Kangaroo 1 oz — ping test & specs

The Silver Kangaroo is the Perth Mint's 1 oz .9999 silver bullion coin. Perth quotes a minimum weight and maximum dimensions; its wide 40.9 mm format gives lower ring frequencies.

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Opens the free tester with this coin preselected — audio never leaves your device.

Official specifications

Weight31.103 g
Diameter40.9 mm
Thickness3.5 mm
Composition.9999 fine silver

Source: Perth Mint. Coin Pinger checks measured weight and diameter against these values.

Expected resonance range

High confidence*
ModeExpected ringRecommended variance
c0d23.34–3.96 kHz±8.5%
c0d37.76–9.09 kHz±7.9%
c0d413.54–15.87 kHz±7.9%

A genuine Silver Kangaroo 1 oz rings within these ranges at its c0d2/c0d3/c0d4 vibration modes, fixed by its size and metal. The recommended variance is how far a genuine specimen's ring can sit from each center — built up in quadrature from real manufacturing tolerance and temperature (under 1%), phone-mic capture reproducibility (≈4%), an extra allowance on the fundamental for minting-asymmetry splitting, and a per-metal model-uncertainty term (largest for .9999 gold, whose modulus is least certain). This coin's band is widened further because the issue is struck at slightly varying thickness across years. The higher modes also carry a small thick-plate centre correction, since a real coin is not infinitely thin. The high-confidence tag reflects how well-established this metal's constants are: Computed from well-established silver elastic constants and cross-checked against same-size sibling coins. These are guidance bands, not exact values — see the methodology for the exact formula, or calibrate your own coin in the app for a specimen-exact reference and tighten each peak per coin.

* These are computed guidance ranges. Certain your Silver Kangaroo 1 oz is genuine but it won't match? Send us its ring — we'll dig in and improve the reference.

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How to ping test a Silver Kangaroo 1 oz

  1. Hold — grip the coin by its center (a nodal point) in a coin ping-test holder so the rim rings freely; a fingertip at the center is a last resort.
  2. Tap — strike the edge with a striker near the microphone.
  3. Read the verdict — MATCH or NO MATCH against the peaks above, plus weight and size checks.
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The physics of the Silver Kangaroo 1 oz ping

Those 3 peaks aren't random. When you strike the coin it flexes as a free disc in fixed patterns called vibration modes — 0 nodal circles with 2, 3 and 4 nodal diameters, written c0d2 / c0d3 / c0d4. Each pattern rings at one frequency.

Where those frequencies land is set by the coin's geometry and metal. For a thin disc, frequency ∝ (thickness ÷ diameter²) × √(stiffness ÷ density). This Silver Kangaroo 1 oz is 40.9 mm across and about 3.5 mm thick in .9999 fine silver, which puts its fundamental (c0d2) near 3650 Hz.

A perfect disc's modes sit near 1 : 2.3 : 3.9; this coin measures 1 : 2.31 : 4.03. That fixed spacing is the fingerprint of a genuine struck disc — Coin Pinger rejects taps that don't fit it (keys, glass, a coin lying on a hard surface).

And it's why a fake can't hide: change the metal and √(E/ρ) changes, so every mode moves. Struck in lead or a plated base metal instead, the ring would land far lower and die out with a dull, short thud — its c0d2 would land near ≈1600 Hz instead of 3650 Hz. Density can fool a scale; the ring can't be faked without the right metal.

We publish this as a High confidence reference. Computed from well-established silver elastic constants and cross-checked against same-size sibling coins.

Free-plate modes per A. W. Leissa, Vibration of Plates, NASA SP-160 (1969, public domain). See how we measure them →
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