Elephants, whales, and many other animals use low frequencies to communicate over very long distances. Low-frequency sounds travel further than high-frequency ones.
It's possible to make a drum in the forest for emergency communication.
TODO: try this to see how well it actually works
- Setup your tarp between two trees, and make sure the ropes are very tight. (the trucker's hitch is good for this)
- Find a suitable branch, maybe 2' long and 1" diameter. If it's sharp at the end, round it over with your knife/axe so it doesn't damage the tarp.
- Bang on the "drum head" with your "drumstick".
Since the tarp is large, it should produce a fairly low note. Tarps that are thicker should produce a better note.
Another possible method:
- Setup your tarp, parallel with the ground, and make sure the ropes are very tight.
- Setup a rope that's vertical. The bottom of the rope should attach at the center of the tarp, and the top of the rope should attach to a tree branch directly above.
- Attach the rope to the center of the tarp using the "improvised tarp attachment point" trick (TODO: find a link for this).
- Make sure the rope is very tight.
- Pluck the rope like a guitar string.
Here, the tarp acts as a speaker diaphragm, and the center rope acts as a voice coil.
For this version, you should be able to vary the frequency of the note by varying the length of the rope.
However, note that even primitive drums included a drum shell of some sort.