Noise travelling

[stevie21]

I'd always thought that someone shouting was a wee bit like throwing a stone : it only went so far & if you were beyond that you wouldn't hear it.
This doesn't explain why you can hear the noise of a football crowd from miles away. If it's too far to hear any of the voices individually, how can we hear the collective noise?

[Loosehead]

you've pretty much answered it yourself. The stone is thrown by much more force. The voices together great a much louder noise and hence it travels much further. The voices are not individual anymore.

[tubeway]

Sound is caused by changes in pressure in the air. If one voice changes the air pressure a certain amount. Then 6000 voices change it by 6000 times more.

[mibn2cweus]

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.

[stevie21]

Pebbles and puddles - I can get my head round that! Cheers.