

Terrestrial Sonar - steanne
http://bldgblog.blogspot.com/2015/04/terrestrial-sonar.html

======
bluusteel
Reminds me of the "talking" drums used in West Africa[1]. Low frequency sound
can travel distances measured in miles.

[1]
[https://en.wikipedia.org/wiki/Talking_drum](https://en.wikipedia.org/wiki/Talking_drum)

------
aaron695
Much as I like a good story.

I call BS.

I tend to think to much energy would be needed to go the distance then reform
in another drum.

[edit] So if all the energy is transferred it'll be the same loudness, but one
would assume it's at least a square root of loss.

An ear on a train line is linearish with neither depth or sideways loss and
still needs a lot of amplification i.e. ear directly on the line. (So it seems
to me from movies.)

