Bizarre reports of US diplomatic staff in Cuba suffering from symptoms resembling brain trauma, allegedly after hearing unsettling sounds resembling scraping metal or insects buzzing, have continued to baffle medical researchers. But a team from the University of Michigan may have come up with a credible explanation for the incident, per the Miami Herald.
Kevin Fu and other members of the university’s Security and Privacy Research Group say that they believe that the sounds could have been caused by improperly placed Cuban spy gear. According to their research, if two inaudible ultrasound surveillance devices were placed too closely together, the resulting interference could become audible—meaning the Cubans may have actually just screwed up rather than intentionally harmed the Americans, the Herald wrote:
Fu and his team used recordings of the sound obtained by The Associated Press and applied reverse-engineering to replicate what was heard by diplomats. By combining various ultrasound signals, they discovered that the resulting distortion produced an audible sound similar to what was heard in the original recording.
“When a second inaudible ultrasonic source interfered with the primary inaudible ultrasonic source, intermodulation distortion created audible byproducts that share spectral characteristics with audio from the AP news,” the university report said.
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“We wondered for a moment if someone might be playing a joke on us,” they wrote in their report. But then they performed a procedure known as “AM demodulation,” and the resulting signal “sounds like an F1 engine.”
In this scenario, either the individual devices themselves or too many of them in close proximity could have had health effects unforeseen by the spies who placed them. (It’s also possible that the audible tones aren’t actually the root of the health problems but a coincidence.)
Fu told the Daily Beast that combined ultrasonic tones could create a 7 kHz noise that “any adult or child can hear,” and that common uses of ultrasound include motion detection (which could activate other surveillance devices).
“It’s a theory that seems a little more practical in that it could be bad engineering,” Fu added.
This explanation does tightly wrap up a few questions about the incident; acoustics researchers say that ultrasound can be deflected by objects like walls and windows, though that doesn’t rule out Cuban intelligence officials from having hidden the devices throughout the embassy or in diplomats’ homes. As noted in a recent review in medical journal JAMA, inflicting neurological damage with infrasound would require massive speakers, and other explanations like chemical and biological agents or mass hysteria don’t seem to be supported by the evidence. Other explanations like unidentified agents aiming exotic microwave weapons at embassy staff are increasingly speculative.
The University of Michigan team argues that there is a “lack of consensus and research on damage caused by ultrasound,” per the Herald, which certainly could lend itself to some sort of accident.
Of course, just because this explanation is parsimonious does not mean it is correct. Fu told the Daily Beast the relevant field is probably too small for him to submit his findings for peer review. Meanwhile, a spokesperson from the University of Miami told the Herald that a Miami Miller School of Medicine research team is following up on prior studies and will present a “high level of comprehensive detail that has not yet been reported.”
It’s far from likely the Cuban government would ever admit a role in the incident if it were indeed involved. US-Cuban relations were just starting to warm after decades of mutual hostility and suspicion, though allegations the Cuban government attacked or was complicit in an attack on the embassy staff have provided a pretext for President Donald Trump’s administration to reverse that trend. For their part, Cuban researchers have said the sounds were probably just humming Jamaican field crickets.