Your analogy of a stones throw is more analogous to the perception of sound than to the behavior of sound waves.
There is a point where the strength of a sound wave falls below the threshold of audibility but the sound wave continues to propagate outward form the source although at a continuously diminishing strength. Sound waves do not necessarily give up their energy as they travel outward from the source, however their energy is distributed over a wider area as they move outward from the point of origin much as the ripples in a pond formed by a pebble diminish in height as they travel away from the point of impact with the energy being dispersed around a continuously widening circle.
Two or more pebbles dropped together will create a larger wave than one alone and the ripple will travel further before diminishing to the same height as a ripple made by one pebble alone.
Just as two or more pebbles make a bigger wave than one alone, more people talking generate more sound energy than a single person talking. The greater intensity of the sound traveling from an arena of shouting people will travel further before dropping to the level of the threshold of audibility.
As a rule of thumb; one person talking at a distance of one metre has the same apparent loudness of ten people talking at 3 metres or 100 people talking from 10 metres away . . . and when the wind is just right this is why you can hear 10000 eager fans hollering from a mile away.