How could the 'sonic attack' on US diplomats in Cuba have been carried out?

If an acoustic weapon is responsible for the 'attacks' on US diplomats it is likely to be ultrasonic, but chemical causes must first be ruled out, say experts

The mysterious "sonic attack" on US diplomats based in Cuba raises questions about what form an acoustic weapon might have taken and the prevalence of such devices in the military.

The US State Department claims that the "attacks" started in autumn 2016 and ended in April this year and had affected at least 16 individuals. Officials said that the symptoms, including hearing loss, headaches and loss of balance, appeared to be the result of sophisticated devices operating outside the range of audible sound. No device nor any perpetrator has been discovered, however.