Loudness of sound is proportional to the square of the amplitude of the vibration producing the sound. For example, if the amplitude becomes twice, the loudness increases by a factor of 4. The loudness is expressed in a unit called decibel (dB). The following table gives some idea of the
loudness of sound coming from various sources.
Normal breathing 10 dB
Soft whisper (at 5m) 30 dB
Normal conversation 60 dB
Busy traffic 70 dB
Average factory 80 dB
Above 80 dB the noise becomes
physically painful.