Question

The sound level measured 30 m from a jet is 140 dB. What is the sound level at 300 m from the jet?

Answer 1

The sound level is `=120dB`

Explanation:

The difference in sound pressure is calculated with the inverse square law

`dL=L_(p1)-L_(p2)=10log_(10)(R_2/R_1)^2=20log_(10)(R_2/R_1)`

where

`dL="difference in sound pressure level (dB)"`

`L_(p1) = " sound pressure level at location 1 (dB)"`

`L_(p2) = " sound pressure level at location 2 (dB)"`

`R1 = " distance from source to location 1 ( m)"`

`R2 = " distance from source to location 2 ( m)"`

Here,

`R_1=30m`

`R_2=300m`

`L_(p1)=140dB`

Therefore,

`dL=20log_(10)(R_2/R_1)=20log_(10)(300/30)=20log_(10)10=20 dB`

`dL=L_(p1)-L_(p2)`

`20=140-L_(p2)`

`L_(p2)=140-20=120dB`