[scottlocklin]

If I were a VC invested in this, I'd want hearing tests on the engineers working on this project; once a month, over time.

Of course, if I were a VC, I wouldn't invest in this, because it is physically retarded on inspection. Whoever did the dil on this is either a fool who doesn't understand basic physics, or was bribed somehow. Off the top of my head a) sound energy falls off as 1/r^2, b) that those sorts of energy densities are almost certainly physically dangerous to more than ears c) sound doesn't propagate well in air at those frequencies; you're basically heating up air d) transducers are not good at turning sound into energy

[jerf]

"a) sound energy falls off as 1/r^2"

No, it doesn't. That's how it falls off when being transmitted perfectly spherically in an environment that won't reflect or refract anything. Consequently, this turns out to be a not-very-useful equation in practice. In particular ultrasound can be beamed just like light, making the "perfectly spherical transmission" not even a close approximation, just as it is not a good approximation for focused lasers. Our intuition doesn't support this because our hearing tops out at frequencies still low enough to do some significant bending around obstacles (though at the higher end if you pay attention you can tell they don't do it as well), so we don't have an intuition of sound acting like a beam, but it can.

There's more to sound than "basic physics", and what you learn in Physics 101 about sound is simplified to the point of total uselessness as in real-life you will never encounter a situation where the prerequisites are met for inverse square falloff.

Mind you, I'm still pretty skeptical, but not about the ability to beam sound. That's established engineering, not wild-eyed craziness.

[scottlocklin]

"In particular ultrasound can be beamed just like light, making the "perfectly spherical transmission" not even a close approximation"

You do realize that energy from a point source of light also falls off like 1/r^2, right?

[jerf]

OK, since conversation has moved on, let me be blunt: You don't know what you're talking about. Your physics 101 education is not the end-all, be-all of physics, and what "point" transmission does doesn't matter because we aren't talking about points. You are in no position to be lecturing people about physics; you are in a position to be lectured to about physics.

[snarfy]

With electromagnetism the energy fall off depends on the radius and the wavelength. If the wavelength is is greater than a certain amount of the radius (the Fraunhofer distance) then the energy fall off is a linear 1/r. This is called the near field.

http://en.wikipedia.org/wiki/Near_and_far_field

[XorNot]

Sound which you can't hear isn't going to be dangerous to the ears in a conventional sense. Of course at electrically significant power levels, it is just potentially dangerous generally.

[tedsanders]

Inaudible sounds can indeed affect and possibly damage hearing. Here's a source: http://news.sciencemag.org/biology/2014/09/sounds-you-cant-h...

Ultrasound can also cause tissue damage at high intensity.

I'd be cautious about making claims that humans are not damaged by high intensity sound, even if inaudible.

Perhaps this is what you mean by saying "a conventional sense" but I just thought I'd expand on your answer in case others read it and get the wrong idea.