Question

If the pressure amplitude of a sound wave decreases by a factor 2, what is the corresponding change of its decibel level?

I keep on getting -5dB.... Is this correct?

Answer 1

The change in decibels is given by
-20 log(ratio of the sound pressure levels) = -20 log2

Answer 2

http://www.ndt-ed.org/GeneralResources/decibel/decibel.htm

\[\Large \Delta I = 20 \log \frac{ 1 }{ 2 }\]

Which with log laws, is equivalent to kropot's value.