Given: Sound Intensity ( I ) =
We know, the approximate threshold of human hearing is at 1kHz. In watts/m^2 it's value is ⁻¹² W/m².
So, we can say, Reference sound intensity = 10⁻¹² W/m².
We have formula for "sound intensity level LI in dB" when entering sound intensity.
LI = 10×log (I / Io) in dB
Plugging values of I and Io in formula.
LI = 10 × log ()
LI = 10 × log (99000000)
= 10 × 7.99564
LI = 79.96 dB.
Therefore, 79.96 dB is the sound level for a noise that has an intensity of 9.9 × 10-5 watts/m2.