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the unit for a relative logarithmic quantity (the logarithm of the ratio between two physical quantities of the same name) that is used in electrical engineering, radio engineering, acoustics, and other branches of physics. It is designated by the letter B and is named after the American inventor of the telephone, A. G. Bell. The number of bels N, which corresponds to the ratio of two energy quantities P1 and P2 (which relate to power, energy, energy density, and so on), is expressed by the formula N = log (P1/P2); for “force” magnitudes F1 and F2 (voltage, current strength, pressure, field strength, and others), it is expressed as N = 2 log (F1/F2). The tenth part of a bel, called a decibel (dB), is usually used.
bell characterThe control code used to sound an audible bell or tone in order to alert the user (ASCII 7, EBCDIC 2F).
deciBelA unit of measurement of the loudness or strength of a signal. One deciBel is considered the smallest difference in sound level that the human ear can discern. Created in the early days of telephony as a way to measure cable and equipment performance and named after Alexander Graham Bell, deciBels (dBs) are a relative measurement derived from two signal levels: a reference input level and an observed output level. A deciBel is the logarithm of the ratio of the two levels. One Bel is when the output signal is 10x that of the input, and one deciBel is 1/10th of a Bel.
A whisper is about 20 dB. A normal conversation is typically from 60 to 70 dB, and a noisy factory from 90 to 100 dB. Loud thunder is approximately 110 dB, and 120 dB borders on the threshold of pain. In 1883, the volcano on the Indonesian island of Krakatoa erupted. A hundred miles away, the sound level reached more than 170 dB, deafening everyone who survived. See dBm.
INCREASE IN POWER LEVELS (WATTS)Formula is dB=10*log(P1/P2)DeciBels Output Signal Strength 3dB 2x 6dB 4x 10dB (1 Bel) 10x 20dB 100x 30dB 1,000x 40db 10,000x ATTENUATION OF AMPLITUDE (VOLTS or AMPS)Formula is dB=20*log(A1/A2)DeciBels Output Signal Strength -3dB 0.707x -6dB 0.5x -10dB 0.316x -20dB 0.1x -30dB 0.032x -40db 0.010x
|Bels and Bells|
|Quite a lot was named after Alexander Graham Bell. Throughout the 20th century, the Bell name was ubiquitous. It will live on with the deciBel.|