Sound travels in waves through the air like waves through water. The higher the wave, the greater its power. The greater the number of waves a sound has, the greater is its frequency or pitch.
The strength of sound, or sound level, is measured in decibels (dB). The frequency is measured in Hertz (Hz) (cycles per second). The human ear does not hear all frequencies. Normal hearing ranges from 20 Hz to 20,000 Hz or, roughly, from the lowest note on a great pipe organ to the highest note on a violin. Our ears hear very low and very high pitched sounds more faintly than those sounds in our normal conversation pitch, between 300 and 4,000 Hz.
The decibel scale is logarithmic (based on powers of ten), not linear like a ruler. Therefore, a small increase in decibels represents a great increase in intensity. For example, while 10 decibels is 10 times more intense that one decible, 20 decibels is 100 times more intense (10 X 10, rather than 10 + 10), 30 decibels is 1,000 times more intense (10 X 10 X 10), and so on. The sound intensity multiplies by 10 with every 10-decibel increase. The reason for such a scale is simply that the human ear is sensitive over such a wide range of acoustic energy that the numbers involved had to be compressed for convenience.
In some ways, the decibel scale resembles the Richter scale for earthquakes. A small numerical increase represents a great increase in intensity.
The ear can detect a very slight change in noise intensity. Even a small reduction in decibels then can make a difference.