# Infra-sound Carrying Quality

I was told that infra-sound has a larger range than audible sound. That is the reason why we hear distant thunders as a deep rumble while closer thunders have an audible "crack" that explodes with high frequency. The thunder is audible in the lower frequencies at longer distances even though most of the energy of the lightning bolt that started the thunder was dumped into the higher frequency modes.

Suppose I want to create a broadcasting device that uses infra-sound to send messages across long distances. I don't have gigantically powerful infra-sound radiators to produce anything even close to a thunder so the range will likely not be many kilometers. And I would like to transmit something more ordered. Music... Or voice, if at all possible.

But this is the thing, I don't know what is possible. A friend of mine told me that this was something called the "carrying quality" of the sound and he also said that my fictional telecommunications device should also consider the possibility of using infra-sound going through the ground rather than the air, since rock is less elastic and the sound wave propagating through it not only would be faster but would experience less dissipation. He said elephants could communicate long distances like that, which I thought was amazing.

I asked him about how that all fits together, carrying quality, elasticity of the medium, sound speed, energy imparted in the signal and the mode of production. He did not manage to give me a straight answer but he said that if I wanted to generate the ground waves, I would need a giant apparatus to stomp the floor in a systematic manner. Might be harder to transmit voice... But what about air? Can I create a "megaphone" for infra-sound voice generation?

So now I'm asking here where I know there are a bunch of physics wizards:

How are the carrying qualities of infra-sound tied to the energy of the signal, the dissipation of the signal along its path, the elasticity of the medium and the range of the wave?

Is there a formula for quantifying these things?

P.S. I know this would be an extra question, but can I transmit voice via infra-sound using a giant megaphone? I'm very curious about that one.