All Problems

Elastic Waves. Acoustics.

Problem 4.188

At a distance r=100 mr=100 \mathrm{~m} from a point isotropic source of sound of frequency 200 Hz the loudness level is equal to L=50 dBL=50 \mathrm{~dB}. The audibility threshold at this frequency corresponds to the sound intensity I0=0.10nW/m2.I_{0}=0.10 \mathrm{nW} / \mathrm{m}^{2} . The damping coefficient of the sound wave is γ=5.0⋅10−4 m−1\gamma=5.0 \cdot 10^{-4} \mathrm{~m}^{-1}. Find the sonic power of the source.

Reveal Answer
Pˉ=4πr2e2γrI0⋅10L=1.4 W, where L is expressed in bels \bar{P}=4 \pi r^{2} \mathrm{e}^{2} \gamma r I_{0} \cdot 10^{L}=1.4 \quad \mathrm{~W}, \quad \text { where } \quad L \text { is expressed in bels }
Prev
Next