well, how about if the sounds are emitted from a small speaker on the person's chest or helmet and the echo captured by an array of small microphones on the same place. Then a microcomputer translates these echoes back into audible sounds in earphones. Im sure someone could learn to "see" these signals. just a thought...

I mean,
- the universe is about 13 billions years old if i'm not mistaken
- we've been able to make enough "noise" to be detected by our closest potential "neighboors" for only a few hundred years at best. So that's a tiny tiny fraction of time compared to the age of the universe. A small little blip.
- it is likely that in 1'000 years from now, or even make it 10'000 years, that if we pick up some noise coming from a distant star system we will be so advanced compared to whatever they might try to tell us that i would compare that to ants for us today: do you really care about the ants communication when you walk in the forest today ? no.
- so my conclusion: the time elapsed between the moment we started to make outgoing noise and the moment we could not care less anymore about such incoming noise is so so so small compared to the age of the universe that the probability to "communicate" with anyone today is extremely low, almost zero.
- we would have to be communicatign with a civilisation which is at par with us in terms of technology and intelligence level, and the time window for this to happen is so bloody small, even if this window is 10'000 years long.

maybe someone can try to help me explaining this better...