Sound waves are emitted uniformly in all directions from a point source. The dependence of sound level β in decibels on the distance r can be expressed as (a and b are positive constants)

β = 10logII0If P is power of sound source thenβ = 10log(P4πr2)I0 where I0 = 10-12 w/m2    = 10 log P4πr2.I0 = 10[log P - log(4πI0.r2)]   = 10[log P - log 4πI0-2 log r] = a-b log rwhere a = 10 log P - 10 log 4πI0 = constant and b = 20 = constant