Sound Devices at Demonstrations: How LRAD Systems Work

During protests in the USA, security authorities use LRAD systems for announcements and crowd control. How do these "sound cannons" work?
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Here's How The Military And Police Use Sound As A Weapon

Sonic weapons known as Long Range Acoustic Devices (LRAD), are used by law enforcement officials as a non-traditional method of crowd control and dispersal in multiple countries across the world. The ...