For one thing, I know math. Among other pursuits, I do signal processing. I’ve done a lot of research during my long life. You can take multiple sinusoidal frequencies and produce interference patterns easily, and you can show the interference patterns mathematically. As a simple example, if you play guitar, then go ahead and barely detune two adjacent strings and try to play the same note. If the two frequencies are off by 1 Hertz, you can hear the interference pattern, and it produces a 1 Hertz beat.
If the interference pattern is 10 kilo-Hertz (kHz), then the beat pattern you hear has that high obnoxious 10 kHz pitch. If I wanted to make a weapon that did damage and used sound, I would use ultrasonic frequencies, and I would use multiple piezo-electric transducers arranged into an array to do it. Now, if the piezo-electric transducers get a little warm and start drifting their frequencies a bit, they will produce an interference pattern, but those lower frequency interference patterns will only contain a small fraction of the power compared to the really dangerous weapon-frequencies.
Not only the damage, but the number of folks as well … a healthy dose of cynicism is OK once in awhile, but in this case your cold water didn’t reach … too many medical issues in too many folks …
That wasn’t actually an answer. I know you can create any waveform over a time window from a fourier series. I understand the basic concepts of what interference patterns are. What I was asking was how can you tell the sound in this recording was produced by multiple sound sources creating an interference pattern?
Thank you for this. Makes sense to me, BWDIK? A rational explanation regardless. The notion that what is recorded is a result of some other ultra high frequency sounds makes a really good avenue of research. As does the idea that really high frequency sounds can cause real damage to human tissue.
Maybe we can test this theory on an embassy in Washington?
Owie… Not good. My cat’s ears pricked up when I played it but my dog slept right through it, but she’s already a bit deaf. You should really put a warning on that audio before posting. Its been over 10 minutes since I played it for only 20 seconds or so, and the ringing in my ears is still happening.
How can I tell? Occam’s razor for one thing, but that’s likely not very satisfying for you to read, so I apologize in advance. You aren’t going to do neural damage with 10 kHz unless the volume is hell-raising paint-blistering wall-heating ENORMOUS. However, if you have reasonable volume at ultrasonic frequencies, you can melt plastic and burn neural tissue without sound, except for the sound of the interference frequencies. Furthermore, the only way to realistically produce the needed volume at these ultrasonic frequencies is with multiple piezo-electric transducers. If they are arranged in a flat array (say, like the flat radar array on an Aegis missile cruiser), then you can modulate the voltage and phase to each transducer and direct a concentrated ultrasonic beam just like they direct radar energy and efficiently paint the sky with radar. Now, this array might be reasonably portable, so you could place it on the side of a building, or in a wall, or the side of a vehicle. Understand that as the transducers heat up, their frequencies can drift apart, and it is this drift that produces the interference frequencies. To keep the frequencies tight together, you’d need to carefully cool the transducers to nearly the same temperature.
If you have two coherent single-frequency sound sources, then with the simplest model, you have one interference frequency. If you have three sources, you have as many as three interference frequencies. As the source quantity increases, the quantity of interference frequencies grows dramatically, because each source can interfere with all the other sources as each source frequency drifts. Furthermore, in extreme cases the interference pattern can also interfere with the sources and produce harmonic beat patterns. Does this make sense to you? It gets more complicated if the transducers produce a spectrum that is not a single frequency.
I can hear it quite clearly, with no after effects. The entire discussion puts me in mind of friends I’ve had over the years who have told me that they can sometimes perceive the tones that come from dog whistles and other devices. I’ve also heard of complaints from younger children to parents that the installation of “sonic” insect and rodent repellents have caused visible discomfort to younger ears.
This is, in my opinion, a form of weapons research and field testing. By whom is a much deeper and more problematic question.
I used to be able to walk into stores and hear near-ultrasonic detectors used for motion detection; anti-burglary devices. That was a very long time ago…early 1980s…but I’ve lost that capability with age. The store manager looked at me like I was nuts until I got a decent microphone and a sound power meter to indicate that it was producing a lot of high-frequency noise. He started asking other customers if they could hear anything, and only a few people could hear it.
IOW, you figure anything people can hear must be an artifact and sound-wave interference is the only artifact that makes sense…right? That seems reasonable. Thanks.
What you want to do is identify the perpetrator. In an ideal world your suggestion is fine. Or for example use a dual/multi mic setup to get directional info. However it would be far more practical and speedy to work with the equipment everybody already carries around with them - their phone - and design a simple app, than design new hardware. Based on GPS and accurate timings alone, you could get an exceptionally accurate idea of where the sound originated if a few people’s phones identified it.
Could be
A) a powerful radar or communications signal being AM-detected. (HAM radio operators know what I am saying).
B) Another kind of microwave signal, maybe used to power ‘passive listening devices’ in the embassy.
Such a device was many years ago fond in the US Moscow embassy.
Does anybody have a .wav recording of the signal ? I dabble in such matters, so it would be fun to see its characteristics.
