What Is a Decibel?
The decibel measures sound pressure or electrical pressure (voltage) levels. It is a
logarithmic unit that describes a ratio of two intensities, such as two different sound
pressures, two different voltages, and so on. A bel (named after Alexander Graham Bell)
is a base-ten logarithm of the ratio between two signals. This means that for every
additional bel on the scale, the signal represented is ten times stronger. For example,
the sound pressure level of a loud sound can be billions of times stronger than a quiet
sound. Written logarithmically, one billion (1,000,000,000 or 10
) is simply 9. Decibels
make the numbers much easier to work with.
In practice, a bel is a bit too large to use for measuring sound, so a one-tenth unit
called the decibel is used instead. The reason for using decibels instead of bels is no
different from the reason for measuring shoe size in, say, centimeters instead of meters;
it is a more practical unit.
Number of decibels
Relative increase in power