Explanation:
The sound intensity can not be in negative however, the intensity level(in dB) can be in negative .
And since, intensity in dB is given as 10log(I/Io).
where as Io = reference intensity.
I = intensity
If I<Io , then log(I/Io) <0
sound intensity obey inverse square law but for intensity in dB is = -20log(r) + 10log(I).