The following excerpt is from an article that originally appeared on Natural Blaze
What caused U.S. embassy employees in the Cuban capital of Havana to lose their hearing?
Reports are surfacing the U.S. embassy staff in Havana has suffered “mysterious physical symptoms,” one being hearing loss. Suggested causes included covert sonic devices.
Extremely high-power sound waves can disrupt or destroy the eardrums of a target and cause severe pain or disorientation. This is usually sufficient to incapacitate a person. Less powerful sound waves can cause humans to experience nausea or discomfort. The use of these frequencies to incapacitate persons has occurred both in counter-terrorist and crowd control settings. 
Some police forces have used sound cannons against protesters, for example during the G20 summit in Pittsburgh   andpost was originally published on this site