A sound wave has an intensity of 0.32 W/m2 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.

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



where I0 is the reference intensity = 10-12 W/m2. We can calculate the sound level bat the location r1 using the above relation:





The sound level at the location r2 = r1 + 0.5 m is band is given by


For a source emitting sound isotropically









But r2 = r1 + 0.5 m.

2-5 Intensity and sound level
Example 2