Sound cannons are actually pretty weird, in that they don’t work like you’d imagine them to work. They produce sound when multiple beams of ultrasound collide with an object, so if they’re pointed at you, you’re the one producing the sound that hurts you. That’s why they’re so effective.
Some people online have done some tests, and thin cardboard appears to be the best way to stop them. Put the thin cardboard before you, and it stops most of the sound. It can be the cardboard from a poster, if you have one.
Ear protection headphones (for workshops) also help, and their effectiveness is enhanced further by wearing small earplugs inside. Active noise cancelling headphones don’t help and can even be counter productive, so don’t use those.
To be a little more pedantic, they send ultrasound frequencies and they “degrade” into regular audible sound waves when they collide with something (combination of harmonic effects and destructive / constructive interference). The reason they send ultrasound instead of using regular directional speakers is because it’s smaller wavelength is easier to aim so much more of the energy moves forwards, so you don’t hear much noise coming from the source itself.
That’s why they work for “crowd control”. A strong enough regular speaker would bother the operator too much.
The noise cancelling part was particularly fascinating. Not only was it ineffective, it amplified the sound. I think its because noise cancelling circuitry relies on the ability to create a signal frequency that cancels out the initial waveform. That’s all well and good, but I think the sound cannons use separate speakers out of phase. Since the noise cancelling headphones produce a signal in phase with the first frequency detected, the microsecond slight delay causes it to be added to a subsequent phase boosting the power.
Sound cannons are actually pretty weird, in that they don’t work like you’d imagine them to work. They produce sound when multiple beams of ultrasound collide with an object, so if they’re pointed at you, you’re the one producing the sound that hurts you. That’s why they’re so effective.
Some people online have done some tests, and thin cardboard appears to be the best way to stop them. Put the thin cardboard before you, and it stops most of the sound. It can be the cardboard from a poster, if you have one.
Ear protection headphones (for workshops) also help, and their effectiveness is enhanced further by wearing small earplugs inside. Active noise cancelling headphones don’t help and can even be counter productive, so don’t use those.
To be a little more pedantic, they send ultrasound frequencies and they “degrade” into regular audible sound waves when they collide with something (combination of harmonic effects and destructive / constructive interference). The reason they send ultrasound instead of using regular directional speakers is because it’s smaller wavelength is easier to aim so much more of the energy moves forwards, so you don’t hear much noise coming from the source itself.
That’s why they work for “crowd control”. A strong enough regular speaker would bother the operator too much.
The noise cancelling part was particularly fascinating. Not only was it ineffective, it amplified the sound. I think its because noise cancelling circuitry relies on the ability to create a signal frequency that cancels out the initial waveform. That’s all well and good, but I think the sound cannons use separate speakers out of phase. Since the noise cancelling headphones produce a signal in phase with the first frequency detected, the microsecond slight delay causes it to be added to a subsequent phase boosting the power.
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