Question

A decibel meter reads 130 dB at a certain position from a jet plane when one engine is turned on.
a) What is the sound intensity at that position?
b) What would be the sound level at the same position if two engines are turned on each having the same intensity as the first?

Answer so far:
I = 10 lg(I/Io)
130 = 10 lg I - lg Io
130 = 10 (lg I - lg Io)
13 = lg I - lg Io
13 = lg I - lg (1*10^-12)
13 - 12 = lg I
1 = lg I
10^1 = I
10 W/m^2 = I

b) 2* 10 W/m^2 = 20 W/m^2

Answer 1

a. db = 10*Log(I/Io) = 130.
10*Log(I/10^-12) = 130.
Log(I/10^-12) = 13.
I/10^-12 = 10^13.
I = 10 W/m^2.

b. db = 10*Log(20/10^-12) = 133.

Doubling the sound intensity increases the sound level by only 3 db.