What does bel mean?
A bel is a logarithmic unit used to express the ratio between two values of a physical quantity such as power or sound intensity, defined as ten times the base-ten logarithm of that ratio. Named in honour of the inventor Alexander Graham Bell, whose pioneering work on the telephone made systematic measurement of signal strength essential, the bel was adopted by engineers in the field of telecommunications and acoustics. Because it describes ratios rather than absolute amounts, the unit is well suited to phenomena like hearing, where human perception responds proportionally rather than linearly to changes in loudness. In everyday and even most professional contexts the bel itself is considered inconveniently large, so measurements are almost universally expressed in decibels, each decibel being one tenth of a bel. Although technically a non-SI unit accepted for use with the International System, the bel remains an important conceptual foundation for anyone studying sound, electronics, or signal processing.
nounA unit for comparing two power levels, equal to ten times the common logarithm of their ratio; one decibel equals one tenth of a bel. It is named after Alexander Graham Bell.
- A logarithmic unit equal to ten times the base-10 logarithm of a ratio of two power quantities, used especially in acoustics and telecommunications.
"The amplifier's output was measured at three bels above its input power."
"Engineers found the signal gain to be two bels across the new system."
"Because the bel is quite large, sound levels are usually quoted in decibels rather than bels."
The plural 'bels' follows regular English noun formation; when used as a unit symbol, 'B', it remains unchanged regardless of quantity.
"Ratios spanning several bels are common in telecommunications engineering."
The bel was named after telephone inventor Alexander Graham Bell — but it proved so large that scientists almost always use just one tenth of it: the decibel.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of bel
The bel is named after Alexander Graham Bell, the Scottish-born inventor of the telephone. The unit was conceived in the early twentieth century at Bell Telephone Laboratories as a convenient way to measure attenuation and power ratios in telephone circuits, and it quickly spread into general engineering use. Its immediate practical descendant, the decibel, became the standard unit worldwide for expressing sound levels and gains.
Related word forms
How bel is actually used
The bel is primarily a technical term used in acoustics, telecommunications, and electronics. In practice it is rarely used directly; the decibel (dB) is the standard working unit. The bel is not an SI unit but is accepted for use alongside SI units.
Easily confused with bel
A bell is a hollow metal instrument that rings when struck, while a bel is a logarithmic unit used to express ratios of power, especially sound intensity.