Bel: The amount of increase in loudness of a sound when its intensity increases ten times is called 1 bel. It is a unit used in the comparison of power levels in electrical communication or of intensities of sound, corresponding to an intensity ratio of 10 to 1.
The Bel was named for Alexander Graham Bell, the discoverer of the telephone. Because the Bel is a huge number, for mainly realistic reasons, the decibel (dB), one-tenth of a Bel, is more frequently used as the unit of measurement.
Decibel: The amount of increase in loudness of a sound when its intensity increases 100.1 times is called 1 decibel. In other words, one-tenth of a bel is called 1 decibel. It is a unit used to measure the intensity of a sound or the power level of an electrical signal by comparing it with a given level on a logarithmic scale.
On the decibel scale, the least audible sound (close to entire silence) is 0 dB. A sound 10 times more influential is 10 dB. A sound 100 times more powerful than close to total silence is 20 dB. A sound 1,000 times more powerful than close to total silence is 30 dB.