decibel
1. a unit for comparing two currents, voltages, or power levels, equal to one tenth of a bel
2. a similar unit for measuring the intensity of a sound. It is equal to ten times the logarithm to the base ten of the ratio of the intensity of the sound to be measured to the intensity of some reference sound, usually the lowest audible note of the same frequency
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
Decibel
A logarithmic unit used to express the magnitude of a change in level of power, voltage, current, or sound intensity. A decibel (dB) is 1/10 bel.
In acoustics a step of 1 bel is too large for most uses. It is therefore the practice to express sound intensity in decibels. The level of a sound of intensity I in decibels relative to a reference intensity IR is given by notation (1).
(1)
Because sound intensity is proportional to the square of sound pressure P, the level in decibels is given by Eq. (2). (2)
The reference pressure is usually taken as 0.0002 dyne/cm2 or 0.0002 microbar. (The pressure of the Earth's atmosphere at sea level is approximately 1 bar.) See Sound pressure The neper is similar to the decibel but is based upon natural (napierian) logarithms. One neper is equal to 8.686 dB.
McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.
decibel
[′des·ə‚bel] (physics)
A unit for describing the ratio of two powers or intensities, or the ratio of a power to a reference power; in the measurement of sound intensity, the pressure of the reference sound is usually taken as 2 ×ばつ 10-4 dyne per square centimeter; equal to one-tenth bel; if P1 and P2 are two amounts of power, the first is said to be n decibels greater, where n = 10 log10(P1/ P2). Abbreviated dB.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
decibel
The unit in which the
level,
4 of various acoustical quantities is expressed.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.
Decibel
a fractional unit of the bel (a unit of relative logarithmic value—the common logarithm of the ratio of two synonymous physical quantities, such as energy, power, or sound pressure). The decibel is equal to 0.1 bel. Symbols: Russian, db; international, dB. In practice the decibel is more often used than the bel, the basic unit.
The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.