The document defines decibels as a unit used to express the intensity of sound waves equal to 20 times the common logarithm of the pressure produced by the sound wave compared to a reference pressure. It explains that the logarithmic scale is used because the change in sound is only noticeable using powers of 10 and it takes about 10 times the intensity for a sound to be perceived as twice as loud. Additionally, it provides guidelines that spending more than 30 minutes at 110 dB can cause permanent damage and recommends using ear plugs if needed.

1. DECIBELS

2. DEFINITION
 noun, Physics.
 1.a unit used to express the intensity of a sound wave, equal to 20
times the common logarithm of the pressure produced by the
sound wave to a reference pressure, usually 0.0002 microbar
 2.a unit of power ratio, the number of units being equal to a
constant times the logarithm to the base 10 of the intensities of
the two sources
 (according to Dictionary.com)

3. WHY USE THE LOGARITHMIC SCALE?
 The change in the sound is only noticeable with using the powers
of 10
 Easier to convert back and forth, nicer numbers
 Takes about 10 times the intensity for it to sound twice as loud

4. DIFFERENCE IN DECIBELS
 Difference in decibels used 10𝑙𝑜𝑔
𝑃2
𝑃1
𝑑𝐵 where log = base 10
 Can see that inverse power ratios will create the opposite
sign of the same number of decibels
 Eg. 10 log
1
2
= −3 𝑑𝐵 10 log 1 = 0 𝑑𝐵
10 log 2 = 3 𝑑𝐵 10 log 10 = 10 𝑑𝐵
http://www.animations.physics.unsw.edu.au/jw/dB.htm

5. SCALE
 Important to protect your ears
 Do not spend more than 30 minutes at 110
dB because the damage can be
permanent
 Use ear plugs if needed

6. REFERENCES
 http://www.animations.physics.unsw.edu.au/jw/dB.htm
 http://www.gcaudio.com/resources/howtos/loudness.html