Template:Sound Amplitude
Amplitude/Pressure
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
Decibels are based on a logarithmic scale.
dB SPL/voltage/current
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 |
| 1 | 0.00 |
| 1.5 | 3.52 |
| 2 | 6.02 |
| 2.5 | 7.96 |
| 3 | 9.54 |
| 4 | 12.04 |
| 5 | 13.98 |
| 6 | 15.56 |
| 7 | 16.90 |
| 9 | 18.06 |
| 10 | 19.08 |
| 20 | 20 |
| 30 | 29.54 |
| 40 | 32.04 |
| 50 | 33.98 |
| 100 | 40 |
| 1000 | 60 |
| 5000 | 73.97 |
| 10000 | 80 |
here are some other good explanations
http://ews64.com/mcdecibels.html
Here is a good dB adding calculator
http://www.mcsquared.com/dbframe.htm this site can also do some other neat o thangs...
