Question

Sound with intensity larger than 120 dB appears painful to a person. A small speaker delivers 2.0 W of audio output. How close can the person get to the speaker without hurting his ears ?

Answer 1

If sound level =120 dB,

then I =intensity =1 $W/m^2$

Given that, audio output =2W

Let the closest distance be x.

So, Intensity $=\left(\frac{2}{4\pi x^2}\right)=1$

$\Rightarrow x^2=\left(\frac{2}{4\pi }\right)$

$\Rightarrow x=40cm$