Decibel
The decibel (dB) is a unitless measurement for expressing ratios. Using
the logarithm allows very large or very small ratios to be represented with
a small number for convenience. Common scientific notation is very similar.
dB is a dimensionless unit, a pure number without a proper unit like feet,
pounds or seconds. Decibels are useful for a wide variety of measurements
especially in acoustics, but also in physics, electronics and other
disciplines.
When used to compare a variable quantity to a known reference quantity, the
measurement is qualified with a suffix. For example, "dBm" indicates that
the reference quantity is one milliwatt.
The bel (B) is mostly used in telecommunication, electronics, and acoustics.
Invented by engineers of the Bell Telephone Laboratory to quantify the
reduction in audio level over a 1 mile (1.6 km) length of standard telephone
cable, it was originally called the transmission unit or TU, but was renamed
in 1923 or 1924 in honor of the laboratory's founder and telecommunications
pioneer Alexander Graham Bell.
The bel was too large for everyday use, so the decibel (dB), equal to 0.1
bel (B), became more commonly used. The bel is still used to represent noise
power levels in hard drive specifications, for instance. Our ears and eyes
both respond logarithmically to acoustic power and luminosity respectively.
Alexander Graham Bell (1847–1922) was a Scottish scientist, inventor, and
innovator. He immigrated to Canada in 1870 and then to the United States
in 1871, a month after he turned 24.
On 1876 February 14 Bell's telephone patent application is filed at the
United States Patent Office. On March 7 United States Patent No. 174,465
is officially issued for Bell's telephone.