What is a decibel?
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Originally Posted by Oaf
Let me put this terms you geeks can understand:
Assuming you have two noise sources(P1 & P2), and the P2 produces twice as much power as P1, the difference in dB is
10 log (P2/P1) = 10 log 2 = 3 dB.
Assuming you have two noise sources(P1 & P2), and the P2 produces twice as much power as P1, the difference in dB is
10 log (P2/P1) = 10 log 2 = 3 dB.
One-tenth of a bel. It is equal to 10 times the logarithm of the power ratio, 20 times the log of the voltage ratio, or 20 times the log of the current ratio. One decibel is the amount by which the pressure of a pure sine wave of sound must be varied in order for the change to be detected by the average human ear. The decibel can express an actual level only when comparing with some definite reference level that is assumed to zero dB.
dB RULES OF THUMB:
Double the power: +3 dB
Halve the power: -3 dB
Ten times the power: +10 dB
One tenth the power: -10 dB
100 times the power: +20 dB
1/100 the power : -20 dB
Approximate Decibel Level Examples
0 the quietest sound you can hear
30 whisper, quiet library
60 normal conversation, sewing machine, typewriter
90 lawnmower, shop tools, truck traffic, 8 hours per day is the maximum exposure (protects 90% of people)
100 chainsaw, pneumatic drill, snowmobile; 2 hours per day is the maximum exposure without protection
115 sandblasting, loud rock concert, auto horn; 15 minutes per day is the maximum exposure without protection.
140 gun muzzle blast, jet engine; Noise causes pain and even brief exposure injures unprotected ears. Maximum allowed noise with hearing protector.
Suppose we have two loudspeakers, the first playing a sound with power P1, and another playing a louder version of the same sound with power P2, but everything else (how far away, frequency) kept the same.
The difference in decibels between the two is defined to be
10 log (P2/P1) dB where the log is to base 10.
If the second produces twice as much power than the first, the difference in dB is
10 log (P2/P1) = 10 log 2 = 3 dB.
If the second had 10 times the power of the first, the difference in dB would be
10 log (P2/P1)= 10 log 10 = 10 dB.
If the second had a million times the power of the first, the difference in dB would be
10 log (P2/P1) = 10 log 1000000 = 60 dB.
Now I think we have really learned something about decibels!
Originally Posted by LagnWagn
Originally Posted by sonicsuby
stupid question..why did this get its own thread?
