Terminology
What is a decibel (dB)?
The decibel is a relative unit, not an absolute. Decibels are used to
compare values of like quantities, usually power and intensity, on a
numerical scale. For example:
-
An intensity ratio of 10 translates to 10 decibels
-
An intensity ratio of 100 translates to a level difference of 20
decibels
-
An intensity ratio of 1000 translates to a level difference of 30
decibels
To be meaningful, a decibel needs a reference point. For example:
-
In water we use a standard reference sound pressure of 1 microPascal
-
In air we use a higher standard of reference of 20 microPascals
-
It is essential that sound levels expressed in decibels include the
reference pressure
Comparison of Various Noise Sources in the Ocean
Noise Sources |
Sound Levels |
Lightning Strike on Water Surface |
260 dB (approximately)[1]
|
Seafloor Volcanic Eruption |
255 dB (approximately)[2]
|
Sperm Whale |
163–180 dB[3]
|
Fin Whale |
160–186 dB[3]
|
Humpback Whale |
144–174 dB[3]
|
Bowhead Whale |
128–189 dB[3]
|
Blue Whale |
155–188 dB[3][4]
|
Southern Right Whale |
172–187 dB[3]
|
Gray Whale |
142–185 dB[3]
|
Note: All decibels (dB) are re 1 µPa at 1 m.