Why does sound die off in air?

Question

please answer with a good explanation.

Answer 1

There are 3 primary causes for sound reduction.

Expansion - everything that expands in 3 dimensions is spreading its energy over a larger area as it moves away from its source. (The formula is 4/3 pi R^2 - the formula for the surface area of a sphere.) Since the same energy is spread over a larger area, the energy at a given point must be less. And since the energy is reduced with the square of the distance, it drops quickly. A sound source that is twice as far away has 1/4 the energy, 3 times as far has 1/9 and so on.

Interference - sound waves are areas of higher and lower pressure in the air. They propegate like the ripples in a pond when you throw a stone in. Just like those waves, if they meet a smooth surface, they reflect with much the same structure - this is an echo. But as the waves start interacting with each other, the high point of one wave hits the low point of another wave, and they cancel each other out. When this happens with a simple wave, it is hardly noticable, which is why echos can sound much like the original sound. But as the waves get more complex, interacting multiple times or reflecting off complex surfaces, the interactions even out and the sound loses its coherence as a wave.

Absorbtion - some surfaces have fine enough or flexible enough features that some of the sound energy is transferred to them with a resulting loss of energy to the original sound wave.

Answer 2

A sound wave spreads out in all directions from the point where the sound was created. The farther away you are, the less intense the wave energy is (how loud the sound is). If there are things in the air that absorb the sound energy, leaves, branches, snow flakes, dust, etc, these will diminish the energy of the wave.

Answer 3

The intensity of the sound waves will get reduced at the rate of inverse square of the distance. Apart from several mass in its propagation absorbers it .Therefore the intensity get reduced almost to 0 after some distance.

Answer 4

It needs atmosphere to be transmitted. The further the sound goes, the more scattered the soundwaves, thus dying out.

For example, if a brass band were standing on Mercury, playing as loud as they could, and you were standing in front of them, you wouldn't hear a thing because Mercury has no atmosphere.