I was concerned to see news of sonic weapons apparently used against the public attending a peaceful vigil in Belgrade. These are powerful tools that could ruin many people's hearing and their lives. I don't know the details of the protest, but I don't like the idea of governments dabbling in how to use these tools against civilians.

I don't expect this to happen in my country. However, in these increasingly turbulent times, we should prepare for such things to happen - at least to someone, somewhere. There's not much public info about sonic weapons, and so there's almost no information for an average innocent citizen, to know what the dangers are or how to protect themselves against harm.

I study sound so I believe I can offer some thoughts. I don't study anything remotely like these weapons hardware, so please consider me only a "half-expert": I have studied sound analysis for around 20 years, BUT primarily recorded/digital sound, not the physical acoustics of devices or their effects on people. Please feel free to find better expert advice - and to tell me about it! Collectively, we should build up some public knowledge on this topic.

Background: LRAD and vortex cannon

I am actually referring to 2 different technologies that have recently been acquired by police forces and military:

1. LRAD ("long range acoustic device") or "sound cannon": a device that emits a narrow beam of sound energy, unlike a standard loudspeaker which radiates energy widely. The narrow focussed beam means that sound can be projected much, much farther and with higher loudness than you might expect. They can be used simply to project audible sound such as a spoken message, but can also be used at high energy to hurt or disorient you.

   (The "LRAD" is a specific commercial product which uses a technique to encode the sound into ultrasound, which then becomes audible when it hits a target. In this article I'm using the term "LRAD" quite generically.)

2. Vortex cannon or vortex ring: a device that creates the same phenomenon as the "smoke ring" that cigar smokers used to blow... but with higher energy. The physics of a vortex ring means that the energy doesn't dissipate much, and the invisible ring (invisible because there's usually no smoke) can travel a long way through a street or into a crowd, with a loud and disorienting "whooshing" sound. I believe that this would have more physical force than an LRAD - you might actually feel it pushing against you as a sudden wave of wind.

These are two very different technologies. But what they have in common is the ability to project energy "invisibly" along a straight line, and a risk of hearing damage. For technical details about how both of these things work, see this article by Black Mountain Analysis.

I don't have any special knowledge of the events in Belgrade on March 15th 2025, but from this analysis by Netzpolotik and the audio analysis shown in the first article I linked, it seems there was at least one LRAD mounted on a jeep, BUT in fact the mysterious loud sound which scattered the crowd is more likely have been a vortex cannon. (Though I didn't see any footage that would show the device that produced it.)

Differences between LRAD and vortex cannon

The vortex cannon is different from the LRAD in how it operates, but also in its effect on you.

The LRAD can project almost any sound, e.g. voices or tones, and I don't believe it's restricted to short bursts. If one of these was fired at you, I think you would hear that sound, coming mysteriously from an unknown direction. It would also be a harsh distorted version of the sound (not a "hi-fi" version).

The vortex cannon, however, is all about projecting a short burst. Looking at the videos from Belgrade, reading the eyewitness accounts, and listening to the sound recordings, you get a consistent message: people heard a very loud roaring/whoosing sound, like a jet engine or a military vehicle suddenly roaring at them at very close range. The effect on the crowd is notable, especially that people all seem to run in a unified direction, so suddenly that they can't all just be following each other. It must be caused by a strong perception that "the jet engine is behind you" from one particular direction, which will be the "middle" of the line of fire.

Some thoughts on how to be prepared

PREPARE IN ADVANCE

• Listen to some examples of what these devices sound like. This way, if it happens to you, you're likely to know what's going on.
• Look at some of the videos (e.g. from Belgrade) to see how crowds tend to react to these devices. Think about how you could be safe in that situation.

ON THE DAY

• Take some hearing protection with you. Don't rely on "noise-reducing" (ANR) headphones, because I don't think they would respond well to high-energy, high-bandwidth, bursts. I don't believe they would protect you. ANR can also make it harder to understand ordinary sound events in a busy situation. Instead, use proper physical hearing protection: ear defenders would be best, but of course that's quite bulky and would mean that you can't hear much at all. You could also use the kind of earplugs that people use for sleeping, made of foam or gel or wax for example -- those would be better than the ones people use for listening to music, but much less protection than ear defenders.
• Maybe you don't want to be wearing ear defenders on every public protest. Indeed you shouldn't have to! You could consider wearing an earplug in one ear when you're in a low-risk situation but want to be a little bit careful.
• Know how to spot the acoustic devices. Often mounted on a van or jeep, they're not very big, but they do also need a non-trivial electric supply.

REACT WELL TO A SONIC WEAPON

• The sonic weapon seems to cause a sudden "flow" of the crowd. Be aware of this - you'll probably be safest if you move with the crowd a little, but try not to panic, try to stay standing, and please protect anyone who falls over.
• Put your hands over your ears, if they're un-protected.
• Get out of the direct line of the shot. Normal sound goes around corners pretty well, but these devices use "coherent" phenomena whose effects mostly fall apart when dissipated around obstructions. So, hiding behind a car or some other big bulky object would help.
• Since these devices are currently so new, many people will not know what's happened. You should tell them. Shout "sonic weapon" or some phrase that will quickly convey the situation.
• The forces that shot the sonic weapon: what will they do next? There are a lot of unknowns. Maybe nothing. But it occurs to me that the effect seen in the Belgrade videos was to clear a channel down the middle of the "beam". I wouldn't be surprised if some forces use this to clear a channel, and then send personnel rushing in through that cleared channel.
• Will there be another shot immediately after? I don't know how quickly these things can be re-charged. A vortex cannon uses fuel, which has a finite supply. I wouldn't expect a lot of rapid shots.

AFTER CARE

The negative effects of these weapons are broadly the same as "ordinary" loud noise trauma. Short-term hearing problems which might or might not become long-term. Disorientation and nausea.

• Follow the standard advice for looking after your hearing after traumatic loud noise. I don't have that advice, but you'll find it online. Give your hearing some time to recover. Visit your doctor.

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That's all I have for now. I hope that there are better experts than me out there who can document more precisely what is known and what can be expected of these things. And I hope governments and other forces will act with restraint and care.