The decibel scale is used to measure sound levels. It is a logarithmic scale where an increase in 10 decibels means the sound is 10 times louder (as measured by sound energy). This means that a 20 decibel difference represents a 100 times louder, etc. The logarithmc scale is used becasue sounds differ greatly n lodness. For example, a whisper is about 30db, conversation about 60db (one thousand times louder) and nearby car engine 90db (one million times loder than the whisper!).
Used in Chap. 14: page 215