/des"euh bel', -beuhl/, n. Physics.1. a unit used to express the intensity of a sound wave, equal to 20 times the common logarithm of the ratio of the pressure produced by the sound wave to a reference pressure, usually 0.0002 microbar.2. a unit of power ratio, the number of units being equal to a constant times the logarithm to the base 10 of the intensities of two sources.3. a unit used to compare two voltages or currents, equal to 20 times the common logarithm of the ratio of the voltages or currents measured across equal resistances. Abbr.: dB, db[1925-30; DECI- + BEL]
* * *▪ unit of measurement(dB), unit for expressing the ratio between two amounts of electric or acoustic power or for measuring the relative loudness of sounds. One decibel (0.1 bel) equals 10 times the common logarithm of the power ratio—i.e., doubling the intensity of a sound means an increase of a little more than three dB. In ordinary usage, specification of the intensity of a sound implies a comparison of the intensity of the sound with that of a sound just perceptible to the human ear. For example, a 90-dB, or 9-bel, sound is nine powers of 10 (i.e., 109, or 1,000,000,000) times more intense than a barely detectable sound. Decibels are also used to express the ratio of the magnitudes of two electric voltages or currents (or analogous acoustic quantities); in this usage one dB equals 20 times the common logarithm of the ratio.The term bel is derived from the name of Alexander Graham Bell (Bell, Alexander Graham), inventor of the telephone.
* * *