![]() The First International Acoustical Conference. ( 2008 edition), page 35 and footnotes h and i on page 36.Ĭommunication, ( July 1924), pages 34-42.ĭecibel–The name for the transmission Unit.īell System Technical Journal, January 1929. Horton (1954), cited below, is a good example of willful Rather than call these units dimensionless, some experts prefer to treat them as having the dimension 1.ĭimensionlessness is a very controversial subject among metrological SI units as a coherent unit of logarithmic decay, leaving the bel outside SI. ![]() In the early 21stĬentury, the CCU considered recommending adding the neper to the list of ![]() The decibel was originally primarily used in Britain and the United It has, however, become so general that it may have to be lived with, at least in the foreseeableĪ variety of other names have been proposed for the decibel, including Power is a violation of the original definition of the decibel. The use of the term “decibel” in connection with a quantity other than The writer, as chairman of the ASA C42 Subcommittee onĬommunication Terms, has been bombarded with letters divided about equallyīetween pleas for extension of the db to new kinds of ratios and pleas Ratios are not the square roots of corresponding power ratios. ![]() These errors can be attributed directly to the practice ofĮxpressing current ratios, or acoustic pressure ratios, in decibels when these Yield results which have differed by several orders of magnitude from estimatesīased on computation. Measurements of power magnitudes have been found to Their profession have contained statements which are demonstrable contradictions Important documents which have been written and reviewed by men eminent in The Use growsįirst International Acoustical Conference (Paris, July 1937)Īdopted the decibel as an international unit at scales of energy and 3.3 dB also describes 467 kilowatts and a reference level 1000 kilowatts. Unit!) from a measurement expressed in dBm. That the dBm is, in fact, a unit is demonstrated by the fact that theĬalculation process can be run in reverse to get milliwatts (no question that that is a Multiply by 10 (we're dealing with power) 10 × −0.331 = −3.3 dBm Later, as the decibel spread beyond the confines of Bell Labs, the difference between 10 and 20Ġ.467 milliwatt into 600 ohms/1 milliwatt into 600 ohms = 0.467 (note, (If you'd like a quick refresher on, check this That is not what “deci-” means in the metric system. The one-tenth in the definition of the decibel occurs in 10 to the This is in accordance with the terminology for the decimal unit, the prefix “deci” being the usual one for indicating a one-tenth relation. The Bell System has adopted the name “decibel” for the “transmission unit,” based on a power ratio of 10. The lowercase “d” comes from the symbol for the metric History please: the first letter that represents a person's name in a symbol is capitalized, while the name of the unit is not. SI units is sanctioned by the CIPM.² The symbol for the decibel was originally “db”, but over time the influence of the SI usage rules has been so strong that they are now applied to the decibel symbol The decibel is not an SI unit, though the use of the decibel with The bel is named for Alexander Graham Bell ( 1847-1922). Recording engineers, forĮxample, refer to “dee-bee-you”, the dBu. Have themselves become part of the names of units. Sometimes the portion after “dB” is printed as a subscript, or follows as a separate word, for example, “dB SPL”. Which property is often shown by adding a suffix to the dB symbol, for example, Levels, measuring several different properties, have been used. Is a reference level explicitly or implicitly specified. Some examples of other dimensionless units are the radian and ppm.¹ Symbol, dB, but see below.Ī measurement in decibels can express an absolute magnitude, provided one side of the ratio ![]() Since the quantities in the ratio always have the same dimensions, the dimensions cancel out the decibel itself is dimensionless. The quantities compared may be two power levels, two voltages, two sound pressure levels, and so on. Radar signal back-scattered from cloudsĪ unit used in electrical engineering and acoustics to express the ratio between two values.Original definition: the transmission unit. ![]()
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