How an acoustic target works and what it measures

An acoustic target works out where the bullet went without a camera, without a screen on the target itself, and without anyone walking downrange to look at the hole. It sounds like a trick — it is precise acoustics. Here is how it works in plain language, and what data about every shot you end up seeing on your phone.

The short version, in four steps

• A bullet travelling faster than sound generates a shock wave in its wake.
• Several microphones around the target (or below it) pick that wave up.
• The system measures how much earlier or later the wave reached each microphone.
• From those fractions of a millisecond it calculates the exact coordinate of the hit — and sends it straight to the app.

The shock wave is not the bang of the shot

When a bullet flies faster than the speed of sound it creates a cone-shaped shock wave, exactly as a supersonic aircraft does. That is a separate wave travelling with the bullet, and it is the one the target’s microphones listen for. The muzzle blast is a different thing: it arrives later, from a different direction, and does not interfere.

Two things follow from this:

• The bullet has to be supersonic. The system registers a shot if the bullet is travelling at 400 m/s or more as it passes the target. What matters is the velocity at the target, not at the muzzle — the bullet slows down over distance.
• Subsonic ammunition is not registered — it produces no shock wave, so there is nothing to detect.

How the microphones calculate the point of impact

What matters here is not loudness but timing. The principle:

1. The bullet passes through the plane of the target and the shock wave spreads out in every direction.
2. Each microphone “hears” that wave at its own moment: the closer it is to the point of passage, the sooner the wave arrives.
3. The electronics measure the difference in arrival times between the microphones, down to fractions of a millisecond.
4. Knowing the geometry of the microphone layout and those differences, the system calculates the coordinate of the hit — ideally down to a millimetre.

In effect the target solves a small geometry problem every time — instantly, for every shot.

Why it only works outdoors

Indoors, the shock wave and the muzzle blast bounce off walls, ceiling and barriers. Echoes build up, reflections overlap, and the microphones can no longer reliably determine where and when the “real” wave arrived. That is why acoustic targets belong on open ranges and shooting grounds. More on this and other criteria in “How to choose an electronic target for a shooting range”.

Where the microphones sit — and why it matters

Sensor placement affects not only accuracy but also how long the sensors survive:

• Around the target frame — the classic layout. Some of the microphones end up inside the impact area and eventually take hits.
• On the horizon line (the Gorizont and Gorizont Mini models) — the microphones are moved down, below the target. The equipment stays outside the impact area, can be shielded by a berm or terrain, and the sensors do not need replacing.

What exactly you see in the app

The interesting part: an acoustic target does not give you a dry “hit / miss” — it gives the full picture of every shot:

• the hit coordinate and the scoring zone;
• misses within about 1 metre around the target — you can see where the shot went;
• the bullet velocity as it passes the target — a real ballistic figure;
• the angle at which the bullet arrived, and the ambient temperature;
• MPI — the mean point of impact of a string — and group size, calculated automatically;
• scores, including IPSC mode, and timing figures.

Why this beats holes in paper

• No walking downrange to inspect holes — the result is on your phone immediately.
• You see the misses, which paper simply does not record (the bullet went past the sheet and you have no idea where).
• MPI and group size are calculated for you, without a ruler and arithmetic.
• The whole history of your strings is saved, so sessions can be compared.

Where millimetre accuracy comes from

The stated accuracy (about 2 mm for Akustik, ~5 mm for Gorizont, ~7 mm for Gorizont Mini) is reached after a short calibration: three sighting shots, a comparison of the points in the app with the real holes, and a correction. It takes a few minutes and is needed the first time you set up at a new place. Without calibration the coordinates will be offset by the unavoidable slight tilt or rotation of the target.