There is a long linear source of sound whose power is $P$ and length is $L$. At point$A$, sound level is $80$ $dB$ .Then at point $B$ sound level will be .... $dB$
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$\mathrm{I}=\frac{\mathrm{P}}{2 \pi \mathrm{rL}}, \beta=10 \log \frac{\mathrm{I}}{\mathrm{I}_{0}}=10 \log \frac{\mathrm{P}}{2 \pi \mathrm{LI}_{0} \mathrm{r}}$
$\beta_{A}-\beta_{B}=10\left[\log \frac{P}{2 \pi L I_{0} r}-\log \frac{P}{2 \pi L I_{0} \cdot 10 r}\right] \,d B$
$80 \mathrm{\,dB}-\beta_{B}=10[\log 10] \mathrm{\,dB}=10 \mathrm{\,dB}$
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