decibel(redirected from Bell unit)
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decibel(dĕs`əbĕl', –bəl), abbr. dB, unit used to measure the loudness of soundsound,
any disturbance that travels through an elastic medium such as air, ground, or water to be heard by the human ear. When a body vibrates, or moves back and forth (see vibration), the oscillation causes a periodic disturbance of the surrounding air or other medium that
..... Click the link for more information. . It is one tenth of a bel (named for A. G. Bell), but the larger unit is rarely used. The decibel is a measure of sound intensity as a function of power ratio, with the difference in decibels between two sounds being given by dB=10 log10(P1/P2), where P1 and P2 are the power levels of the two sounds. The faintest audible sound, corresponding to a sound pressure of about 0.0002 dyne per sq cm, is arbitrarily assigned a value of 0 dB. The loudest sounds that can be tolerated by the human ear are about 120 dB. The level of normal conversation is about 50 to 60 dB. The decibel is also used to measure certain other quantities, such as power loss in telephone lines.
A logarithmic unit used to express the magnitude of a change in level of power, voltage, current, or sound intensity. A decibel (dB) is 1/10 bel.
In acoustics a step of 1 bel is too large for most uses. It is therefore the practice to express sound intensity in decibels. The level of a sound of intensity I in decibels relative to a reference intensity IR is given by notation (1).
The neper is similar to the decibel but is based upon natural (napierian) logarithms. One neper is equal to 8.686 dB.
a fractional unit of the bel (a unit of relative logarithmic value—the common logarithm of the ratio of two synonymous physical quantities, such as energy, power, or sound pressure). The decibel is equal to 0.1 bel. Symbols: Russian, db; international, dB. In practice the decibel is more often used than the bel, the basic unit.
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.|