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The concept of decibel originates from telephone engineers who were working with power loss in a telephone line consisting of cascaded circuits. The power loss in each circuit is the ratio of the power in to the power out, or equivalently, the power gain is the ratio of the power out to the power in.

A rule of thumb that is useful to remember is that 10 dB is a power ratio of 10. Any time a power is increased tenfold, it is increased by 10 dB; thus, a 200W power amplifier will put out 10 dB more electrical power than a 20W amplifier, and its sound power output will also increase by 10 dB.

Another way to think of decibels is to think in terms of percentages. We all know what 10 percent means, and nobody thinks of percentages as being quantities of anything. A DECIBEL is nothing more than a power change of 27 percent, 3 dB is a power change of 100 percent, and 10 dB is a power change of 1,000 percent.

The human ear's response to sound level is roughly logarithmic (based on powers of 10), and the dB scale reflects that fact. An increase of 3dB doubles the sound intensity but a 10dB increase is required before a sound is perceived to be twice as loud. Therefore a small increase in decibels represents a large increase in intensity. For example - 10dB is 10 times more intense than 1dB, while 20dB is 100 times more intense than 1dB. The sound intensity multiplies by 10 with every 10dB increase.

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The chart below shows the actual Sound Power Level reduction for each decibel removed

Following is a list of dB readings from various sources to act as a non-scientific point of reference: