I was burning trash in a barrel today about 100 feet from a Cat generator I noticed as I was standing behind the barrel with some rather large flames that the sound of the generator was muffled. I moved around some and determined that it must be the flames or heat muffling it. Although we have quite a few containers around and the sound from the generator can bounce around and can vary within a few feet. This was a direct line of sight however.
I just stepped out side and checked to see if without the flames/heat if the sound was still effected. It was not. Seems the heat did something.
So does heat distort/shield sound?
Well, sound is a propagation of a change in air pressure, so the rapidly rising heat of a large flame disturbs the air enough to affect sound movement - higher frequencies more so than lower ones, that’s why it sounded muffled. Similarly, the wind also affects sound, depending on the direction, you may or may not be able to hear a person standing far away.
As to reflections, that is far less of a concern outside than inside, because you usually only get one reflection off any surface, as opposed to the dense pattern of second, third and fourth reflections in a room that we call reverb.
It seems to me that such burning could create a thermocline or related phenomena, which can reflect or distort sound. The ocean’s thermocline layer can bounce sonar.