Why there is a limit to how far sound wave can travel
The speed of sound in air is indeed relatively constant under normal conditions, but there's a significant factor that limits how far sound can travel over long distances: attenuation.
Attenuation refers to the gradual decrease in the intensity of a wave as it propagates through a medium. In the case of sound waves in air, several factors contribute to attenuation, which limits the distance over which sound remains audible:
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Divergence: As sound waves travel away from their source, they spread out in three dimensions. This means that the same amount of sound energy is distributed over an increasingly larger area, leading to a decrease in sound intensity with distance.
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Air Absorption: Air is not a perfect conductor of sound, and it absorbs some of the sound energy as the waves pass through it. The higher the frequency of the sound, the more pronounced this effect becomes.
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Scattering and Reflection: Sound waves can scatter in different directions or reflect off obstacles, such as buildings, hills, and the ground. These interactions can lead to sound being redirected away from the listener or absorbed by surfaces, reducing the overall intensity.
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Noise Pollution: In urban environments, noise pollution from various sources, such as vehicles and industrial machinery, creates a background of constant noise that interferes with our ability to hear distant sounds.
The net result is that sound waves gradually lose energy as they travel through the atmosphere, which limits how far they can propagate. This is why, even if the speed of sound remains constant, sound becomes quieter and eventually inaudible at greater distances. For example, at typical atmospheric conditions, a loud sound might become difficult to hear at distances of a few kilometers, and it's often lost in the background noise at greater distances.
To transmit sound over very long distances, techniques like amplification, focusing, and controlling atmospheric conditions are used, such as in large outdoor concerts or military applications. Additionally, for communication over extremely long distances, electromagnetic waves like radio waves are more practical because they don't suffer from the same attenuation issues as sound waves.