The Decibel scale (dB) is a logarithmic measure of levels and it is surprising how a tiny increase in Decibel level is actually a large increase in level. For instance an increase of 3dB is equivalent to an increase in level perceive by the ear and brain as double the sound level. Therefore only a small increase in decibels should not be seen as a minor increase in sound level. The ear responds in a logarithmic fashion and this is why this way of measuring is used to establish sound levels. Using a linear scale would mean very large and very small numbers being used and is not meaningful for measurement of sound.

Here is an example:

73dBa is the level of a noisy city street
76dBa is twice that level
79dBa is four times that level
82dBa is 8 times that level
85dBa is 16 times that level
88dBa is 32 times that level
91dBa is 64 times that level
94dBa is 128 times that level
97dBa is 256 times that level
100dBa is 512 times that level
103dBa is 1024 times that level (The level of noise produced by an F-15 taking off measured in my garden).

Other levels:

A quiet room 30dBa
Normal converstaion in a quiet room 55dBa
Kitchen with washing machine on spin 65dBa
quiet car passing steadily at 30MPH 68dBa