Ping Test (Sound Test)
Also: Sound test, Ring 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 struck 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 due to their crystalline metal structure: when lightly struck, they vibrate at a high, long-sustained frequency - a bright, clear tone that rings on for several seconds. Fake coins made of inferior alloys or with a tungsten core, by contrast, produce a dull, short sound with no sustain. Additional test methods such as density measurement or the magnet test should be used to complement it.
Physical Background
The sound of a coin 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 resonance. Counterfeit materials such as copper-zinc alloys, lead or tungsten damp the sound more strongly, which is why 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 resonance |
Note: The tungsten sound is not trivial to distinguish - since tungsten has a density very close to that of gold (tungsten: 19.25 g/cm³, gold: 19.32 g/cm³), the ping test is only of limited value for gold-plated tungsten counterfeits. Here ultrasonic testing or X-ray fluorescence analysis is essential.
How to Perform It
The ping test can be done without any tools, but can be made considerably more precise with a smartphone app:
- Freehand method: Balance the coin on your fingertip or a fingernail (minimal damping from body contact). Tap it lightly with the edge of another coin, a pencil or your fingernail. Listen to the tone and pay attention to length, pitch and purity.
- 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 can 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 due to the complex coin geometry (typically 1,000-6,000 Hz for common bullion coins), but the principle remains the same.
Limitations of the Method
The ping test is a useful quick filter, not a conclusive proof. It fails with:
- Tungsten-gold counterfeits (same density, similar acoustic properties in certain geometries)
- Coins with core damping from air pockets or cavities (rare high-quality counterfeits)
- Damaged or heavily oxidised coins whose acoustic properties are altered
- Coins in a capsule or blister, when the test is damped by packaging material
For a reliable finding, the ping test should always be combined with a coin weight check, size check and, where possible, the coin authenticity check. For high-value pieces, professional methods such as X-ray fluorescence or ultrasound at a recognised refinery are advisable.
In Brief
The ping test is a fast, free initial check for precious metal coins and provides good indications of obvious counterfeits with gold and silver coins - but it does not replace instrument-based testing, particularly not with tungsten-based counterfeits or high-value numismatics.