A friend once told me that as a kid, while staying at a lake house, he was able to hear normal conversation going on across the lake, about a mile away.
The weather conditions were clear and calm, with a glassy surface on the lake.
This sounds right for the sound waves to be 'ducted' across the lake.
Perhaps there was a temperature inversion just above the surface of the lake, which created the ducting effect.
Or, is this something completely different from ducting of U/VHF radio waves over long distance using low power?
After all, sound waves are not electromagnetic waves; they are percussion waves that can only travel through a medium.
What you think?
Frank <KE2KB>