As you move closer to the source of a sound, the sound becomes louder due to the way sound waves spread and interact with the surrounding medium. This phenomenon is known as the inverse square law of sound.
According to the inverse square law, the intensity of sound decreases as you move away from the source. When you double the distance from the sound source, the intensity decreases by a factor of four. Conversely, as you reduce the distance from the source, the intensity of the sound increases.
There are a few reasons why sound becomes louder as you move closer to the source:
Concentration of energy: As sound waves propagate outward from their source, they spread out in a spherical manner. This means that the same amount of sound energy is distributed over a larger area as you move farther from the source. When you move closer, you reduce the distance over which the energy is spread, leading to a higher concentration of energy and thus increased loudness.
Decreased spreading: Sound waves experience spreading or divergence as they travel through a medium. This spreading causes the sound energy to be distributed over a larger area, resulting in a decrease in intensity. When you move closer to the source, the spreading is less pronounced, so the sound energy remains concentrated over a smaller area, leading to a higher intensity and increased loudness.
Reduction of obstacles and interference: As you move closer to the source of a sound, you may also reduce the number of obstacles or objects that can absorb or reflect the sound waves. These obstacles can cause the sound waves to scatter or be absorbed, reducing their intensity. By moving closer and minimizing these obstacles, you allow more sound waves to reach your ears, resulting in a louder perception of the sound.
It's important to note that the loudness of a sound also depends on factors such as the power of the sound source and the frequency content of the sound. However, the decrease in distance from the source is a primary factor in the perceived increase in loudness.