How does the sound pressure level (SPL) change if the distance from the sound source is doubled?

A. It remains the same.
B. It decreases by 6 dB.
C. It decreases by 3 dB.
D. It increases by 3 dB.

When the distance from the sound source is doubled, the sound pressure level decreases by approximately 6 dB due to the inverse square law. The formula used to calculate the change indicates that intensity drops to a quarter of its original value. Therefore, the answer is option B: it decreases by 6 dB.
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Answered by Anonymous | 2025-07-17

The sound pressure level (SPL) is an important concept in physics that describes how intense a sound is, typically measured in decibels (dB). The SPL is related to the distance from the sound source due to how sound waves spread out as they travel.
When the distance from a sound source is doubled, the sound pressure level decreases by 6 dB.
Here's why:

Inverse Square Law : Sound intensity (and hence SPL) follows the inverse square law. This law states that the intensity of sound decreases proportionally to the square of the distance from the source. So, when the distance is doubled, the intensity becomes 1/4 of the original.

Decibel Calculation : The decibel scale is logarithmic. A decrease in intensity by a factor of four corresponds to a 6 dB decrease:
Δ L = 10 ⋅ lo g 10 ​ ( Intensity Ratio )
Given the intensity ratio is 1/4 when the distance is doubled, we calculate:
Δ L = 10 ⋅ lo g 10 ​ ( 0.25 ) ≈ − 6 dB


In summary, if the distance from a sound source is doubled, the sound pressure level decreases by 6 dB. Therefore, the correct option is: "It decreases by 6 dB."

Answered by BenjaminOwenLewis | 2025-07-21