Sound level when distance doubles
You move from 1 m to 2 m away from a small sound source in open air. About how much does the sound level drop?
Answer B: explanation for every choice
A
A 3 dB drop corresponds to halving intensity, which assumes intensity falls as 1/r.
B
Correct. Intensity falls as 1/r², so doubling distance gives ¼ the intensity, and 10 log(4) ≈ 6 dB.
C
A 10 dB drop corresponds to a 10-fold decrease in intensity.
D
A 20 dB drop corresponds to a 100-fold decrease in intensity.
TakeawayPoint source: I ∝ 1/r². Doubling distance → about −6 dB.
Equation usedSound level
See your set score →Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID cp87.