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Decibel - Definition | | Decibel - Definition: Encyclopedia II - Decibel - Definition | | An intensity I or power P can be expressed in decibels with the standard equation
where I0 and P0 are a specified reference intensity and power.
If PdB is 10 dB greater than PdB0 then P is ten times P0. If PdB is 3 dB greater, the power r ...
See also:Decibel, Decibel - Definition, Decibel - Standards, Decibel - Merits, Decibel - History of bels and decibels, Decibel - Uses, Decibel - Acoustics, Decibel - Electronics, Decibel - Optics, Decibel - Telecommunications, Decibel - Seismology, Decibel - Typical abbreviations, Decibel - Absolute measurements, Decibel - Relative measurements, Decibel - Reckoning, Decibel - Round numbers, Decibel - The 4 → 6 energy rule, Decibel - The 789 rule, Decibel - −3 dB ≈ ½ power, Decibel - 6 dB per bit, Decibel - dB cheat sheet, Decibel - Reference | | | Decibel, Decibel - 6 dB per bit, Decibel - Absolute measurements, Decibel - Acoustics, Decibel - Definition, Decibel - Electronics, Decibel - History of bels and decibels, Decibel - Merits, Decibel - Optics, Decibel - Reckoning, Decibel - Reference, Decibel - Relative measurements, Decibel - Round numbers, Decibel - Seismology, Decibel - Standards, Decibel - Telecommunications, Decibel - The 4 → 6 energy rule, Decibel - The 789 rule, Decibel - Typical abbreviations, Decibel - Uses, Decibel - dB cheat sheet, Decibel - −3 dB ≈ ½ power, Equal-loudness contour, ITU-R 468 noise weighting, Noise (environmental), Signal noise, Sound pressure level, Weighting filter—discussion of dBA, Decibel magazine | | |
| | | Decibel: Encyclopedia II - Decibel - Definition
Decibel - Definition
An intensity I or power P can be expressed in decibels with the standard equation
where I0 and P0 are a specified reference intensity and power.
If PdB is 10 dB greater than PdB0 then P is ten times P0. If PdB is 3 dB greater, the power ratio is very close to a factor of two.
For sound intensity, I0 is typically chosen to be 10−12 W/m2, which is roughly the threshold of hearing. When this choice is made, the units are said to be "dB SIL". For sound power, P0 is typically chosen to be 10−12 W, and the units are then "dB SWL".
In engineering, voltage V or pressure p can be expressed in decibels with the standard equation
where V0 and p0 are a specified reference voltage and pressure. Note that in physics, these equations are considered to give power in decibels, and it is then incorrect to use them if the electrical or acoustic impedence is not the same at the two points where the voltage or pressure are measured. In this formalism, decibels are always a measure of relative power or intensity, and the value is the same regardless whether power or voltage/pressure measurements are used.
If VdB is 20 dB greater than VdB0 then V is ten times V0. If VdB is 6 dB greater, the voltage ratio is very close to a factor of two.
For sound pressure, p0 is typically chosen to be 2x10−5 N/m2, or pascals (Pa) which is roughly the threshold of hearing. When this choice is made, the units are said to be "dB SPL".
Decibel - Standards
The decibel is not an SI unit, although the International Committee for Weights and Measures (BIPM) has recommended its inclusion in the SI system. Following the SI convention, the d is lowercase, as it is the SI prefix deci-, and the B is capitalized, as it is an abbreviation of a name-derived unit, the bel, named for Alexander Graham Bell. Written out it becomes decibel. This is standard English capitalization.
Decibel - Merits
The use of decibels has three different merits:
- It is more convenient to add the decibel values of, for instance, two consecutive amplifiers rather than to multiply their amplification factors.
- A very large range of ratios can be expressed with decibel values in a range of moderate size, allowing one to clearly visualize huge changes of some quantity.
- In acoustics, the decibel as a logarithmic measure of ratios fits well to the logarithmic dependence of perceived loudness on sound intensity. In other words, at all levels of loudness, increasing the decibel level by the same amount creates approximately the same increase in perceived loudness — humans perceive the increase from 20 dB to 25 dB as being about the same as the increase from 90 dB to 95 dB, for example. This is known as Stevens' power law.
Other related archives1923, 1924, A-weighting, Acoustics, Alexander Graham Bell, Bell Telephone Laboratory, Decibel magazine, Eardrums, English, Equal-loudness contour, Frequency weighting, ITU-R 468 noise weighting, International Committee for Weights and Measures, Jet airplanes, Link Budget, Noise (environmental), Psychologists, RMS, Richter scale, SI, Shock waves, Signal noise, Sound, Sound pressure level, Stevens' power law, TNT, Units of measure, Weber-Fechner law, Weighting filter, Windows, acoustics, amplifiers, amplitude, antenna, apparent magnitude, arithmetic, attenuators, audio amplifier, bit, body, bomb, buffer amplifier, circuits, clipping, component, dB SIL, dB SPL, dB SWL, dB(A), dB(B), and dB(C), dBFS, dBW, dBm, dBrn, death, digital audio, dimensionless unit, dipole, ear, earthquakes, electric field strength, electrical power, electronics, engineering, explosions, femtowatt, fiberoptic, fibre, frequency, frequency weightings, full scale, gain, hard drive, harmonics, healthy, hearing, hertz, human, hurricanes, input resistance, intensity, isotropic, isotropic antenna, jackhammers, jet engines, kilowatt, laboratory, logarithm, logarithmic, logarithmic measure, loss, loudness, meter, metre, microvolt, million, milliwatt, moment magnitude scale, mosquito, natural logarithm, neper, nuclear bombs, optical, optical density, output resistance, percent, percentages, physics, power, preferred numbers, pressure, quantization noise, radio, ratio, ratios, reference noise, resistance, response, short scale, signal-to-noise ratios, sonic booms, sound, sound intensity, sound pressure, sound pressure level, sound pressures, space shuttle, square metre, telecommunication, telecommunications, threshold, threshold of hearing, tornadoes, trillion, unit, volcanic eruption, volcanoes, voltage, watt, wire, μPa
 Adapted from the Wikipedia article "Definition", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki |
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