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The Epic Interactive Encyclopedia 1998
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Epic Interactive Encyclopedia, The - 1998 Edition (1998)(Epic Marketing).iso
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D
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Decibel
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1992-09-02
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Unit (symbol dB) of measure, used originally
to compare sound densities, and subsequently
electrical or electronic power outputs; now
also used to compare voltages. An increase of
10 dB is equivalent to a 10-fold increase in
intensity or power, and a 20-fold increase in
voltage. A whisper has an intensity of 20 dB;
140 dB (a jet aircraft taking off nearby) is
the the threshold of pain. The difference in
decibels between two levels of intensity (or
power) L1 and L2 is 10 log10(L1/L2); a
difference of 1 dB thus corresponds to a
change of about 25%. For two voltages V1 and
V2, the difference in decibels is 20
log10(V1/V2); 1 dB corresponding in this case
to a change of about 12%. Commonly such
differences are given now not as ratios but
as absolute values; for example, 10 dBV
corresponds to the voltage level V1 with V2
set equal to 1 volt.