After several months of investigation, the US has concluded that its diplomats in Cuba have been “exposed to an advanced device that operated outside the range of audible sound and had been deployed either inside or outside their residences,” reports the Associated Press. The effect was so severe that some of the diplomats had to return home from Cuba early due to hearing loss.

Last week, Rex Tillerson, the US secretary of state, elaborated that the diplomats had been the victims of “health attacks”. At least one Canadian diplomat in Cuba has also been treated for hearing loss.

The Cuban government has said it wasn’t responsible for any possible attack, but that it has launched an “exhaustive, high-priority, urgent investigation”.

Part of the difficulty in unravelling what may have occurred is that the history of the development of acoustic weapons is shrouded in rumour and conspiracy, says Steve Goodman, the author of Sonic Warfare.

There is some research showing that frequencies just outside the human hearing range can have effects including hearing loss, concussion and nausea.

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