Ping Test
Also: Ring test, Ping test, Coin ping, Bell test
The ping test is a non-destructive authenticity check that uses the characteristic ringing sound of a coin when lightly tapped to distinguish genuine precious-metal coins from counterfeits.
The ping test is one of the oldest and simplest methods for checking the authenticity of precious-metal coins. Silver, gold and platinum possess a characteristic acoustic property owing to their crystalline metal structure: when lightly tapped, they vibrate at a high, long-lasting frequency – a bright, clear tone that resonates for several seconds. Counterfeit coins made of inferior alloys or with a tungsten core, by contrast, produce a dull, short sound with no ring. Additional testing methods such as density measurement or the magnet test should be used alongside it.
Physical background
A coin's sound is determined by its natural frequency, which depends on material, mass, geometry and alloy composition. Precious metals such as silver and gold have a high speed of sound in the solid state and low internal damping (damping coefficient). The result is a long, bright ring. Counterfeit materials such as copper-zinc alloys, lead or tungsten dampen the sound more strongly, so the tone sounds either considerably lower, shorter or tinny.
| Metal | Speed of sound (approx.) | Sound character |
|---|---|---|
| Silver (999) | 3,650 m/s | Bright, long ringing |
| Gold (999) | 3,240 m/s | Warm, medium-length ring |
| Copper | 3,810 m/s | Similarly bright, but shorter decay |
| Tungsten | 5,180 m/s | High, hard sound – no harmonic decay |
| Lead | 1,210 m/s | Very dull, no ringing |
Note: The tungsten sound is not trivial to distinguish – because tungsten has a density very similar to gold (tungsten: 19.25 g/cm³, gold: 19.32 g/cm³), the ping test is only of limited value with gold-plated tungsten counterfeits. Here ultrasonic testing or X-ray fluorescence analysis is essential.
Procedure
The ping test can be done without tools, but can be made considerably more precise using a smartphone app:
- Free-hand method: Balance the coin on a fingertip or fingernail (minimal damping through body contact). Lightly tap it with the edge of another coin, a pencil or a fingernail. Listen to the tone and note its length, pitch and clarity.
- App-assisted method (recommended): Apps such as Bullion Test or CoinScan record the tone via microphone and compare the frequency spectrum with reference values for known coin types. A deviation of more than a few hertz in the fundamental tone may indicate a counterfeit.
- Comparison method: Place a genuine reference coin of the same type and weight alongside and compare both sounds directly.
Fundamental frequency f ≈ (speed of sound v) / (2 × coin diameter d)
Example silver ounce (d ≈ 40 mm): f ≈ 3,650 m/s / 0.08 m ≈ 45,625 Hz (overtone spectrum)
The actually audible fundamental frequency is considerably lower owing to the complex coin geometry (typically 1,000–6,000 Hz for common investment coins), but the principle remains the same.
Limitations of the method
The ping test is a useful quick filter, not conclusive proof. It fails with:
- Tungsten-gold counterfeits (same density, similar acoustic properties in certain geometries)
- Coins with core damping due to air pockets or cavities (rare high-quality counterfeits)
- Damaged or heavily oxidised coins whose sound properties are altered
- Coins in capsules or blisters, where the test is dampened by packaging material
For a reliable result, the ping test should always be combined with a coin weight check, a size check and, where possible, the coin authenticity check. For valuable pieces, professional methods such as X-ray fluorescence or ultrasound at a recognised refinery are recommended.
In brief
The ping test is a quick, free initial check for precious-metal coins and gives good indications of obvious counterfeits with gold and silver coins – but it does not replace instrumental testing, especially not with tungsten-based counterfeits or high-value numismatics.