bel the unit of level of quantity proportional to power when the base of the logarithm is ten. Also, the unit of level of a field quantity when the base of the logarithm is the square root of ten GRM: n. SBL/EXP: B Note: non Sl unit; the submultiple decibel, dB, is commonly used instead of the bel, 1 dB -0.1 B ; examples of power-like quantities are sound power and sound energy. Examples of field quantities are sound pressure and voltage