As a black audio engineer, I thought I would take a second to talk about Long Range Acoustic Devices (LRADs), which are effectively sound cannons. They have been used to disperse crowds in the past, so I want to talk about them now as they can permanently damage your hearing. 
LRADs were originally invented as a weapon of war after the USS Cole was attacked in 2000. They are now occassionally used as devices to disperse large crowds (i.e. protests). They can be used for either making announcements (like a large bullhorn) or emit a loud tone.
LRADs are able to make sound in excess of 160dB. For context, the sound of a shotgun being fired is typically around 120dB. A plane typically takes off at around 120-140dB. At 160, your eardrums can burst after brief exposure.
Even a second of exposure at 140dB can cause permanent hearing loss. Exposure to sounds this loud can also cause migranes and dizziness. Some report that after being exposed, loud sounds like sirens cause them to have similar symptoms months after exposure to LRADs.
Regular earplugs can protect you at lower ranges, but once you pass around 100dB, the only way your ears will be safe is if you are using similar ear protection as people working in airports.
If you see one of these devices (typically either on top of police vehicles or held by an officer), please get away as fast as you can. If you are going to protests, I'd recommend bringing earplugs even if these devices aren't present to protect yourself from crowd noise.
Stay safe out there y'all. When your hearing is damaged, it lasts a lifetime.
Also one more thing: here's an article about the NYPD's use of these devices being challenged in federal court after being used on a BLM protest in 2014: nbcnews.com/news/us-news/p…
