The decibel (dB) is a unit that is used to measure electrical power. A dB is
one-tenth of a Bel, which is a larger unit of sound named for Alexander Graham
Bell. The dB is measured on a base 10 logarithmic scale
. The base
increases ten-fold for every ten dB measured. This scale allows people to work
more easily with large numbers. A similar scale called the Richter Scale is
used in measuring earthquakes. For example a magnitude 6.3 earthquake is 10
times stronger than a 5.3 earthquake.
Calculating dB
The formula for calculating dB is as follows:
dB = 10 log10 (Pfinal/Pref)
- dB = The amount of decibels. This usually represents a loss in power such
as when the wave travels or interacts with matter, but it can also represent a
gain as when traveling through an amplifier.
- Pfinal = The final power. This is the delivered power after some process
has occurred.
- Pref = The reference power. This is the original power.
There are also some general rules for approximating the dB and power
relationship:
- An increase of 3 dB = Double the power
- A decrease of 3 dB = Half the power
- An increase of 10 dB = Ten times the power
- A decrease of 10 dB = One-tenth the power