Intensity of Sound

How much does a sound’s intensity diminish as you move away?

When the total energy in the sound wave remains the same as the sound spreads over a sphere the intensity decreases as the area of the sphere increases. The area of a sphere is proportional to the square of its radius, so the intensity is inversely proportional to the square of the distance. That is, sound intensity diminishes according to the inverse square law. For example, if a person stands 1 meter (3.3 feet) away from a source, the sound intensity might be an arbitrary unit of 1. If that same person moved so she was 2 meters (6.6 feet) away from the source, the intensity would be 1 over the square of the distance, or one fourth the intensity. Again, if the listener moved 3 meters (9.8 feet) away, the intensity would be one ninth it was at the 1-meter mark.


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