It may not be acoustical. It could be microwave. Theoretically (and I’m out of my depth) frequency modulated microwaves could move the fluid in the head, causing acoustic like side effects.
Or it could be microwaves being used to excite a local acoustical device, kind of like the famous State Dept. Seal bug, but in reverse.
It is considered by the alternative press to already exist (almost 20 years, now) and there have been numerous books that cover this subject. Easily found. Basically the microwave RF as a carrier frequency and then audio modulation.
I believe there was a fully blown test done in this area, a while back. I tend to read physorg every day, and I think it was covered. almost 100% sure on that one. Meaning, it hit the mainstream.
Mainstream does not mean real, it just means mainstream. Like life itself, the vast majority of existence is outside of the mainstream. Things can be real when they are not widely known. Popularity does not make fact or reality, unless a person anchors themselves in herd stupidity.
And, to add, things in the mainstream are considered quite psychotic and unreal at times, by those who do not center their lives in the mainstream. And so on.
Back to the microwave carrier audio modulation thing. Basically, black ops stuff, the subject of ridicule, barbs and spit flung at the explorers of the fringe data.
Always remember that the CIA, deeply involved in DARPA, was the actual creator of the term ’conspiracy theory’. And that many of the inventions considered to be conspiracy by the mainstream, and as reported by the fringe..turned out to be real. Ie, the ’heart attack gun’, to remotely trigger a heart attack in people in range (same room, etc) turned out to b a real functional invention. And much much more.
Eg, to say there are ’controls’ injected into forums on website, to control the discussion is considered conspiracy theory.
Yet the military of the USA admits freely and directly on this subject, and also stating that the biggest area of warfare to open up for the next 100 years, is cyberspace, forums, and similar stuff that has yet to evolve.
so, various groups freely admit to being involved in some forms, in an attempt to steer the narrative out of areas they don’t want explored. Ridicule, straw man arguments, ganging up, being a moderator, and so on. All avenues of narrative control that are outside of common noticing.
And many hundreds more of articles and pages of text to find and read on, if you want t know more about this very real and very current subject.