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Researchers Provide Likely Explanation For the 'Sonic Weapon' Used At the US Embassy In Cuba (ieee.org)

An anonymous reader quotes a report from IEEE Spectrum: Last August, reports emerged that U.S. and Canadian diplomats in Cuba had suffered a host of mysterious ailments. Speculation soon arose that a high-frequency sonic weapon was to blame. Acoustics experts, however, were quick to point out the unlikeliness of such an attack. Among other things, ultrasonic frequencies -- from 20 to 200 kilohertz -- don't propagate well in air and don't cause the ear pain, headache, dizziness, and other symptoms reported in Cuba. Also, some victims recalled hearing high-pitched sounds, whereas ultrasound is inaudible to humans. The mystery deepened in October, when the Associated Press (AP) released a 6-second audio clip, reportedly a recording of what U.S. embassy staff heard. The chirping tones, centered around 7 kHz, were indeed audible, but they didn't suggest any kind of weapon. Looking at a spectral plot of the clip on YouTube, Kevin Fu, a computer scientist at the University of Michigan, noted some unusual ripples. He thought he might know what they meant.

Fu's lab specializes in analyzing the cybersecurity of devices connected to the Internet of Things, such as sensors, pacemakers, RFIDs, and autonomous vehicles. To Fu, the ripples in the spectral readout suggested some kind of interference. He discussed the AP clip with his frequent collaborator, Wenyuan Xu, a professor at Zhejiang University, in Hangzhou, China, and her Ph.D. student Chen Yan. Yan and Xu started with a fast Fourier transform of the AP audio, which revealed the signal's exact frequencies and amplitudes. Then, through a series of simulations, Yan showed that an effect known as intermodulation distortion could have produced the AP sound. Intermodulation distortion occurs when two signals having different frequencies combine to produce synthetic signals at the difference, sum, or multiples of the original frequencies. Having reverse engineered the AP audio, Fu, Xu, and Yan then considered what combination of things might have caused the sound at the U.S. embassy in Cuba. "If ultrasound is to blame, then a likely cause was two ultrasonic signals that accidentally interfered with each other, creating an audible side effect," Fu says. "Maybe there was also an ultrasonic jammer in the room and an ultrasonic transmitter," he suggests. "Each device might have been placed there by a different party, completely unaware of the other."

50 of 112 comments (clear)

  1. Ultrasonic transmitter and jammer? by DigiShaman · · Score: 3, Interesting

    Who would be using the transmitter? Who would be using a jammer. Moreover, which nation-state/s would bother with using ultrasonic in an age of cheap RF based technologies?

    --
    Life is not for the lazy.
    1. Re:Ultrasonic transmitter and jammer? by Anonymous Coward · · Score: 3, Interesting

      It looks like the spy agencies working there at the embassy did it to themselves and everybody else working there. CIA puts their thing in. The NSA theirs. Some military intelligence puts theirs in.

      Cubans sit back and eat popcorn.

      The Cuban government must be laughing their asses off.

    2. Re:Ultrasonic transmitter and jammer? by PolygamousRanchKid+ · · Score: 4, Interesting

      Who would be using the transmitter?

      The Cubans.

      Who would be using a jammer.

      The embassy staff . . . to thwart the Cubans.

      Moreover, which nation-state/s would bother with using ultrasonic in an age of cheap RF based technologies?

      Folks who don't want their bugs found because they are constantly transmitting.

      --
      Schroedinger's Brexit: The UK is both in and out of the EU at the same time!
    3. Re:Ultrasonic transmitter and jammer? by K.+S.+Kyosuke · · Score: 4, Funny
      So far, so good, but...

      Cubans sit back and imagine eating popcorn.

      FTFY?

      --
      Ezekiel 23:20
    4. Re:Ultrasonic transmitter and jammer? by NicknameUnavailable · · Score: 3, Interesting

      Think sound cancellation in ultrasonic instead of audible frequencies. It only cancels perfectly at one location, and has a lag - those things can fuck up your senses if they are out of tune (it's just more often applied in sound canceling headphones than whole-room devices, so the target area where the sound actually cancels that you're familiar with is at the right spot - in whole room devices they rarely actually work correctly over the whole room unless designed specifically for the shape and size of the room and the location of other sound sources and are synced to the same audio source as the other sound source so they know what to cancel before it gets there.)

    5. Re:Ultrasonic transmitter and jammer? by PolygamousRanchKid+ · · Score: 5, Funny

      Can the "host of mysterious ailments" be really caused by a sonic source?

      The Cubans are researching new technology and are staging a "Brown Note" attack against the US Embassy!

      https://en.wikipedia.org/wiki/...

      "Mr. President, we must not allow...a Brown Note gap!

      Coming soon, to DARPA . . .

      --
      Schroedinger's Brexit: The UK is both in and out of the EU at the same time!
    6. Re:Ultrasonic transmitter and jammer? by nospam007 · · Score: 4, Funny

      They should have used Detectors Of Gruesome Sounds (DOGS) which would have alerted them to the fact immediately.

    7. Re:Ultrasonic transmitter and jammer? by nospam007 · · Score: 1

      "More important: Can the "host of mysterious ailments" be really caused by a sonic source (no matter the root cause?)"

      Sure. I for example have a 'mysterious ailment' called Tinnitus and nobody else can hear it.

    8. Re: Ultrasonic transmitter and jammer? by Anonymous Coward · · Score: 5, Interesting

      No, you're missing the point.

      The idea is that somebody, luke the Cubans or Russians or Chinese, planted an ultrasonic snooping device... which are harder to sweep/scan for than RF based communications.
      Then somebody like the CIA or NSA installed an ultrasonic jammer, to prevent use of such bugs.
      But the frequencies interfered and resulted in amplification of some wavelengths which ended up causing the symptoms.

      No, no hard proof. But a damn site more plausible than someone building, installing, and using some sort of audio weapon to fuck people up for no reason.

    9. Re:Ultrasonic transmitter and jammer? by omnichad · · Score: 1

      If anything, if the pulses are due to phase cancellation it's because it's some sort of sonic beamforming weapon - barely audible to everyone but the victim. And the perceived frequency may not be ultrasonic or even in the same range as the individual beams. The recording device would not be in the place that puts everything in phase - it would be highly targeted.

    10. Re:Ultrasonic transmitter and jammer? by omnichad · · Score: 1

      You can't cancel out varying frequencies with any accuracy. You jam them by producing noise in the same frequency range, so the signal is harder to draw out.

      synced to the same audio source as the other sound source so they know what to cancel before it gets there

      If you can be accurate enough and synced enough to determine the location of the transmitter, you just remove the transmitter.

    11. Re:Ultrasonic transmitter and jammer? by Cro+Magnon · · Score: 3, Funny

      That would be a shitty thing to do!

      --
      Slow down, cowboy! It has been 4 hours since you last posted. You must wait another few hours.
    12. Re:Ultrasonic transmitter and jammer? by vtcodger · · Score: 1

      In reality, the Cubans suggested that the US State Department to bring the FBI in to see if they could get to the bottom of the problem. (No, I don't know why the Cubans might think the FBI might know anything about sonic weapons).

      Do the Cubans have the US offices and residences bugged? Of course they have the US offices and residences bugged. Why would they not? You can probably hear the plumbing talking to the air conditioners and every other electronic device if you listen real hard at night. Did they unleash some weird sonic weapon of the gringos? Even if they had such a device why would they use it on diplomats instead of on folks who are actually a threat?

      --
      You can't see ANYTHING from a car, You've got to get out of the goddamned contraption and walk...Edward Abbey
    13. Re: Ultrasonic transmitter and jammer? by vtcodger · · Score: 1

      One thing that the slashdot description doesn't mention. Just having two transmitters in a room or building does not produce intermodulation products. You need some sort of non-linear "device" as well to combine the signals and emit the IM products -- in radio terms, a mixer. (That's not the same thing as an audio "mixer" BTW). I'm having a little trouble imagining what could act as a mixer and emit significant 7kHz audio signals. And wouldn't folks be able to find the mixer if not the transmitters just using their ears? 7KHz is well within the audio range for all but a few of us elderly folks.

      --
      You can't see ANYTHING from a car, You've got to get out of the goddamned contraption and walk...Edward Abbey
    14. Re: Ultrasonic transmitter and jammer? by TechyImmigrant · · Score: 1

      Yep. Walls too.

      --
      I should use this sig to advertise my book ISBN-13 : 978-1501515132.
    15. Re: Ultrasonic transmitter and jammer? by rahvin112 · · Score: 1

      An audio weapon that experts say is impossible to build mind you. All the audio experts the press consulted said the scenario the state department came up with is highly unlikely and probably impossible.Such weapons don't exist and can't because of physics.

  2. I got it by Anonymous Coward · · Score: 1

    Interference caused by multiple ultrasonic toothbrushes running simultaneously.

  3. It's "The Thing"! Run for your lives! by PolygamousRanchKid+ · · Score: 4, Funny

    Someone must have "left a few of these "Things" somewhere in the building:

    https://en.wikipedia.org/wiki/...

    --
    Schroedinger's Brexit: The UK is both in and out of the EU at the same time!
    1. Re:It's "The Thing"! Run for your lives! by WallyL · · Score: 1

      Someone must have "left a few of these "Things" somewhere in the building:

      https://en.wikipedia.org/wiki/...

      Brings new meaning to the expression, "Internet of Things," doesn't it?

  4. You know they've been trying to find the problem by drinkypoo · · Score: 3, Interesting

    They looked for stuff like that, and didn't find it. Unless they are wholly incompetent, that's not the problem.

    --
    "You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
  5. False. Not a "likely" explanation, but "possible" by daveschroeder · · Score: 2

    Also based on 6 seconds of audio and nothing else, doesnâ(TM)t rule out an attack or deliberate emplacement for a particular purpose, and doesnâ(TM)t change the outcome.

  6. Heinlein's Razor by Oxygen99 · · Score: 4, Insightful

    Never attribute to malice that which is adequately explained by stupidity (Although don't rule out malice)

    --
    I had a dream, bright and carefree, but now there's doubt and gravity
    1. Re:Heinlein's Razor by PPH · · Score: 4, Funny

      That's Hanlon's Razor and ....

      Oh, never mind.

      --
      Have gnu, will travel.
  7. Re:You know they've been trying to find the proble by PolygamousRanchKid+ · · Score: 1

    They looked for stuff like that, and didn't find it.

    "Testing shows the presence, not the absence of bugs" -- Edsger W. Dijkstra

    Unless they are wholly incompetent, that's not the problem.

    Like Dijkstra says, they can only find what they are looking for.

    If there is something they don't know about . . . they don't know how to look for it . . . so they can't find it.

    So the Cubans have something our spooks don't know about. We have only noticed the "collateral damage" it has cause . . . not the thing in itself. Kinda sorta like looking at the traces left by wacky sub-atomic particles.

    --
    Schroedinger's Brexit: The UK is both in and out of the EU at the same time!
  8. Obvious by burtosis · · Score: 1

    If only someone at the time had put this together and stated it publically. What dosent add up here is the sensors mentioned in the white paper are all very low power. You dont cook peoples thinking jelly with a half watt transmitter or two throughout a building, though they do have the potential to be as annoying as old fluorescent lights. To mess up people you would need extremely high power sensors running all the time, something I find extremely hard to believe "was accidental with 2 or more parties not knowing" when a 50 cent sensor would clearly tell you something is broadcasting extreme amounts of energy.

  9. Dumb by ArchieBunker · · Score: 1

    The first paragraph says ultrasound doesn't travel well in air and does not cause pain. Second paragraph suggests an ultrasound transmitter and possibly jammer? What would be the point of any of these devices if they can't transmit very far?

    --
    Only the State obtains its revenue by coercion. - Murray Rothbard
  10. Re:You know they've been trying to find the proble by oh_my_080980980 · · Score: 1

    LMOL yeah the cubans have something the NSA does not know about....think about that for a second....

  11. You started with the premise.... by oh_my_080980980 · · Score: 1

    "This technical report analyzes how ultrasound could have..."

    So it's not surprising you came up with a result that supports that conclusion. It would be more convincing if you were looking for something else and then came up with that conclusion, when you eliminated other explanations.

    Why China was involved is curious thing...

  12. Re:actually the noise was from my DAMN balls by Anonymous Coward · · Score: 1

    His mom ordered you to start sucking her balls? Or did she order you to start sucking his balls?

  13. Re:You know they've been trying to find the proble by jbmartin6 · · Score: 1

    They have the whole world to draw from, perhaps someone loaned it to them for a field test.

    --
    This posting is provided 'AS IS' without warranty of any kind, implied or otherwise.
  14. Re:Doubtful by MrKaos · · Score: 5, Interesting

    Why would an IMD product be more harmful than any other audio signal of normal intensity and spectral content? That question needs to be answered before this theory can be taken seriously.

    Standing waves. I've been spending the last three years working in this space with audio processing, before I even open the paper I said to myself "I bet intermodulating waveforms" is a factor and there it was on the second page. I will most certainly read this whole paper however I thought I'd share some of my experiences that were a by-product of what I was trying to understand.

    Out of curiosity I tried the experiment on myself and a few friends and found that if you hit the right frequency with a person, they will practically hit the roof and run away if they have any form of Tinnitus. I did a spectral analysis of the waveform and the best I can describe it is like audio teeth, waveforms with a specific Q, amplitude and frequency separation. I could'nt see anyone handling more than a few seconds of it, I have no doubt you would be very sick in much less than a minute.

    If there were two devices they would cancel AND reinforce certain audio spectrum within the human hearing range thus you would get a combination of modulating and standing waveforms would be *really* disorientating, anything more than 5watts at that frequency range would be nasty. Just moving around in the room would make it oscillate.

    It's not just humans and please don't hold this against me, I love dogs too, but not when they bark until 5am and sleep all day while I am driving down a freeway fatigued. Complaining to neighbors doesn't work but an intermodulating waveform oscillating between 23k and 25k works in under 10 seconds. No neighborly confrontation required.

    The last thing I found is that it doesn't have to be actual damage to your hearing to produce the effect. I have my hearing tested often, I know exactly where the damage is and the effect is not necessarily related to damage.

    A final point though is wind turbines. I think the effect is the same however it is intermodulating infrasound with very long waveforms relating to the characteristics of the turbine blades in different turbines interacting with each other. I would not live near these devices any more than living next to a main road, it will slowly make you sick.

    Obviously my pithy experiments aren't controlled so I'm interested in what this paper has to say, maybe it can answer some questions I have.

    --
    My ism, it's full of beliefs.
  15. Re:You know they've been trying to find the proble by Moskit · · Score: 1

    They _said_ they did not find. Saying is not the same as not finding, especially for politics/espionage/...
    Basic example - sometimes you leave a known bug to disseminate wrong information.

  16. TV remote controls by ctrl-alt-canc · · Score: 2

    Ancient TV RC used ultrasound transmitters. They are no more used in the civilized world, but maybe in Cuba are still there. People of the embassy were busy with two remote controls in a fight to decide which TV sitcom to view and...

    1. Re:TV remote controls by PPH · · Score: 5, Interesting

      Back in my days working on secret stuff, meeting room windows were equipped with piezoelectric transducers used to defeat laser inferometer microphones. It's possible that our embassy was so equipped. This would explain one ultrasonic source. Possibly even multiple sources in rooms with lots of windows and poorly installed systems.

      --
      Have gnu, will travel.
  17. what? by YayaY · · Score: 1

    So, it was an ultrasonic weapon that use intermodulation as a targeting mechanism. Suggesting that this just happened by accident at US embassy is ridiculous at best.

    If the OP explanation was probable, it would also occur randomly at other location. We haven't heard about that so far.

    --
    Votator.com implements a fair voting scheme (free
  18. Good by pele · · Score: 1

    Now we wait for diplomats to provide a swift and loud apology just like they switfly and loudly rushed to accuse them of having created a sonic weapon to attack their staff.

    Oh btw how efficiently does ANY sort of sound travel through bullet-proof glass that they have on pretty much all embassies?

  19. Re: You know they've been trying to find the probl by Type44Q · · Score: 1

    So the Cubans have something our spooks don't know about.

    Plaintains?

  20. Re:You know they've been trying to find the proble by Hal_Porter · · Score: 2

    Rogue states like Cuba and North Korea don't necessarily need to develop this sort of thing for themselves - they could just let in Russian or Chinese intelligence agents who'd have something they'd need to test.

    It's like the reverse case of the Cold War where a lot of US allies - naming no names but the CPU in your cellphone or laptop was either invented, designed or manufactured in one - allowed US intelligence personnel in to test some clever intelligence gathering ideas on the USSR, PRC or their allies in return for access to the information they gathered.

    This being intelligence stuff it's all a bit legally dubious even in the West. God knows what happens in places where the intelligence agencies can openly ignore the law like China, Russia, Cuba or North Korea.

    For example Peter Wright described a plan to convert a bust of Lenin into an ultrasound reflector - the idea being the reflected ultrasound would be modulated with an audio signal, the audio signal being the sound around it -

    https://spyinggame.me/2012/07/...

    As to what else went on inside the embassy, perhaps MI5 picked it up by electronic means, perhaps not. Peter Wright describes a delicious plan devised by MI5 in the 1950s, using new technology to modify an ordinary object so that it would reflect sound waves; carrying no transmitter or receiver itself, the object was virtually undetectable. Why not modify some valuable object along these lines and give it to the Soviet ambassador? Wright consulted someone who knew the ways of the Soviet diplomatic community and had also been with MI5: Klop Ustinov, father of the actor. Ustinov suggested a bust of Lenin or a model of the Kremlin, something so sacred that the Soviets wouldn't be tempted to sell it. Lenin was vetoed ("the smooth contours of Vladimir Ilyich's skull were too rounded to be sure of reflecting sound waves," Wright tells us) and ultimately the FO abandoned the project, for reasons we do not learn.

    I.e. the idea of using a microwave or ultrasound reflector as a remote microphone has been around for some time.

    --
    echo -e 'global _start\n _start:\n mov eax, 2\n int 80h\n jmp _start' > a.asm; nasm a.asm -f elf; ld a.o -o a;
  21. Re:Doubtful by jenningsthecat · · Score: 1

    Why would an IMD product be more harmful than any other audio signal of normal intensity and spectral content? That question needs to be answered before this theory can be taken seriously.

    The harm isn't specifically because it's an 'IMD product'. The structure of the human ear and the human body are such that even fairly loud sounds at ultrasonic frequencies have little perceptible effect. But the presence of two or more high-amplitude ultrasonic sources of different frequencies can actually create, via intermodulation, very loud audible frequencies in the ears or the head. These frequencies ARE within the range of human hearing. And they can be even more devastating than high-amplitude sounds 'out in the world', because they are being generated very close to, or actually inside of, the ear itself.

    --
    'The Economy' is a giant Ponzi scheme whose most pitiable suckers are the youngest among us and the yet-unborn.
  22. Re:Amplitude is to High by jenningsthecat · · Score: 1

    Intermod products are always much lower than the source signals... Bad guess guys.

    Bad guess AC, but thanks for playing. In systems that are designed to be linear, (audio amplifiers, for example), intermod products are very low. But in systems which are very non-linear, either by design, (as in RF mixers), or by accident, (equipment faults, or badly overloaded ears), Intermod products can be within a few dB of the primary signals.

    --
    'The Economy' is a giant Ponzi scheme whose most pitiable suckers are the youngest among us and the yet-unborn.
  23. OMG, it's not sonic by Theaetetus · · Score: 1

    Audio engineers and neuroscientists have been saying this since the story first came out: it's not a sonic weapon. It's not some "unknown type of sonic weapon" or a "sonic weapon that utilizes unknown physics" or "leaves scientists baffled by new sonic weapon." It's almost certainly a microwave transmission, probably to energize a passive listening device like The Thing:
    It's highly directional and so only affects one person in a room, without anyone else noticing anything. Moving their heads from one position causes the symptoms to go away. That can fit with both ultrasonic intermodulation and microwaves, but none of the other symptoms can: remember, intermodulation products are lower amplitude than the modulating signals. So to create these allegedly loud noises, unless you're talking about such high power that the transmitting devices are the size of shipping containers and they're in the same room, they're not going be the result of acoustic coupling. So "directionality" and "some victims hear ringing" is really the only thing that supports the 'sonic weapon' theory.
    But no, the auditory hallucinations are instead almost certainly a result of tissue heating in the temporal lobe, which is why they also experience effects like dizziness and nausea, tingling sensations, headaches, memory problems, and brain swelling. The effects have been compared to concussions and CTE, which would easily look like tissue heating. That's really easy to accomplish with a microwave, and can be done from outside in a van or from a nearby building.

    1. Re:OMG, it's not sonic by eaglesrule · · Score: 1

      In addition, the AP clip was debunked:

      Cell phone recordings of the alleged sonic attack were provided to an Associated Press reporter by an anonymous source in the State Department. But the sounds were identified by Yamile González Sánchez, an official at the Ministry of Public Health, and physicist Carlos Barceló Pérez, a professor at the National Institute of Hygiene, as those made by local insects, which they recorded on the scene. Moreover, the sounds, all in the audible range (about 7 kilohertz), would have overdriven the microphone—preventing it from recording—if they were loud enough to damage hearing.

      So Wu was analyzing the sound made by cuban crickets.

  24. Ultrasonic noise by Khyber · · Score: 1

    "Among other things, ultrasonic frequencies -- from 20 to 200 kilohertz -- don't propagate well in air"

    That's why dogs can hear my dog whistle from about a mile off, right?

    --
    Still waiting on Serviscope_minor to wake up to fucking reality and realize that Jessica Price isn't going to fuck him.
    1. Re:Ultrasonic noise by iggymanz · · Score: 1

      No, they hear it because it's fucking loud, and can be painful or damaging to dog's ears at close range. Stop using it, asshole.

  25. I don't get what the damn mystery is here by danlor · · Score: 1

    This tech has been around for decades. Its currently in use.

    Here is a demo from decades ago:
    https://youtu.be/4eZVF1ouTT4?t...

    Ultrasonic beat waves/interference is what this looked like from the beginning. Reverse engineering isn't necessary to discover this.

  26. Ultrasonics? by Bruce+Perens · · Score: 2

    A couple of 1970-style ultrasonic intrusion alarm sensors might make the same sounds by hetrodyning together. It is more than likely that such things could be found in the embassy. The embassy building was constructed in '53 and re-occupied by the U.S. in '77.

    I've seen no credible explanation for the injuries reported to have occurred to personnel there. The U.S. has monitored for various sorts of energy, RF, sound, light, since Theremin's Great Seal Bug (the "Thing") which the post above refers to. The absence of any credible cause makes this difficult to believe in. Sure the Russians and Cubans are capable of this sort of thing, but that the U.S. failed to detect it is difficult to believe.

  27. It doesn't take scientists to explain a hetrodyne. by Bruce+Perens · · Score: 1

    The explanation of the number of Ph.D. scientists it took to explain "Duh, it's a Hetrodyne!", and then to not even use the correct language (intermodulation distortion is an effect of hetrodyning signals in a supposedly linear circuit, not the hetrodyne itself), is really pathetic.

    You could get a better explanation from the average radio ham in clearer language.

  28. Re:False. Not a "likely" explanation, but "possibl by rahvin112 · · Score: 1

    Except of course all the experts in audio, ultrasound and RF say such a weapon is impossible to build. What the US state department described was a sound weapon that couldn't be heard, destroyed hearing and affected peoples minds and was targeted as specific people. Sound, ultrasound and RF cannot be controlled in a manner like that or cause those symptoms and that kind of distance.

    The state department cooked up a fanciful weapon to describe these events but everyone that was an expert said it was impossible. What happened here was likely far more mundane.

  29. Re:Doubtful by evil_aaronm · · Score: 2

    I lost my hearing back in '84 to spinal meningitis. I now have a cochlear implant to hear things. I'm curious if these waveforms would bother me because my hearing isn't "natural." Push comes to shove, I can either connect a music source in-line, which blocks all external sound, or just turn my CI off. Would that be a useful defensive mechanism?

  30. Re:Doubtful by MrKaos · · Score: 2

    I lost my hearing back in '84 to spinal meningitis. I now have a cochlear implant to hear things. I'm curious if these waveforms would bother me because my hearing isn't "natural."

    That's a really good question, short answer is I don't know but I could have a guess.

    Push comes to shove, I can either connect a music source in-line, which blocks all external sound, or just turn my CI off. Would that be a useful defensive mechanism?

    I bet that feature comes in handy sometime ;)

    I think it will depend on three factors: 1. the microphone will have a non linear response in a limited range, 2. the circuitry of the device and 3. the frequency spectrum it offers you.

    I think that these devices are mainly aimed at you being able to hear other people so the audio spectrum would be concentrated around 3-4khz where human speech roughly resides so therefore I suspect you would be pretty safe from those sorts of attacks. However if the frequency response is extended and the device produces a harmonic you might perceive it but not it's effects. That's my guess.

    I finished reading this paper, fascinating. The spectral analysis is very similar to what I saw, I think my HF drivers and DACs are a bit better and can produce higher outputs (not that you need it) than what they have and also the distance *between* the drivers is a factor as well.

    My method was different than what they were using because I was trying to understand perception to make things sound pleasing not to destroy people. That said, the paper concludes it wasn't on purpose and if you think about it, that's reasonable. I'd imagine there was a lot of pressure and focus on those diplomats it's not unreasonable to conclude there was a bunch of equipment in that room causing all sorts of unwanted interactions.

    --
    My ism, it's full of beliefs.