A sound wave has an
intensity of 0.32 W/m^{2} at a distance r from the source. If the
distance is increased by 0.50m, the sound level is decreased by 2.0 dB.
Assume the loudspeaker emits sound isotropically, find the distance r.

a. The distance r = m

The intensity I of sound is related to the sound level b through the relationship:

where I_{0} is the reference
intensity = 10^{-12} W/m^{2}. We can
calculate the sound level b_{
}at the
location r_{1} using the above relation:

The sound level at the location r_{2}
= r_{1 }+ 0.5 m is b_{2
}and is_{
}given by

Answer

For a source emitting sound isotropically

But r_{2}
= r_{1} + 0.5 m.

2-5 Intensity and sound level

Example 2