Measured in dB Decibels
The softest sound we as humans can hear is about 20 micro pascals (20µPa or 0 dB re 20µPa ) the loudest sound we as humans can tolerate is about 200 Pa(120 dB re20µPa) this is a 10,000,000:1 ratio. This is why Bel labs decided to use a different scale to represent the numbers. They used the deciBel or 1/10 of a Bel.
decibels as a power ratio The Bel was defined as the logarithm of a power ratio and was named after Alexander Graham Bell. The deciBel is 1/10th of a Bel. Since the range of human hearing is so large a logarithmic scale was implemented.
Sound Pressure and common sound sources
|140 dB SPL||.45 APC Colt pistol (25 ft.)|
|130 dB SPL||50 HP Siren (100 ft.)|
|120 dB SPL||Threshold of pain|
|110 dB SPL||Typical rock concert|
|90-100 dB SPL||Platform of subway station as train arrives. Loud classical music|
|80 dB SPL||Person Shouting|
|60 dB SPL||Average conversation (5 ft)|
|40 - 50 dB SPL||Average suburban home at night|
|30 dB SPL||Very quiet whisper|
|20 dB SPL||Extremely quiet Recording Studio|
|0 dB SPL||Threshold of hearing. Anechoic Chamber http://www.bell-labs.com/org/1133/Research/Acoustics/AnechoicChamber.html|
Decibels are based on a logarithmic scale.
dB = 10 * log (P1^2 + P2^2) = dB = 20 * log (P1 + P2)
1dB small change in power
6dB doubling of power
20 dB roughly twice as loud ten times the voltage
|Voltage, current or SPL||dB|
here are some other good explanations
Here is a good dB adding calculator
http://www.mcsquared.com/dbframe.htm this site can also do some other neat o thangs...