Decibel is a logarithmic unit used to describe the
ratio of the signal level - power, sound pressure, voltage, intensity, etc.
Most signal systems -
as sound power or sound intensity, human speech, sonar, microwaves, radio
signals and fiber optics - can be described by
- transmitting power
- transmission path loss
- receiver sensitivity
Transmitting power,
path loss and receiver sensitivity are absolute power values - Watts in the SI
system.
The Definition of Decibel
Decibel is a
logarithmic unit used to describe the ratio of the signal level - power, sound
pressure, voltage or intensity or several other things.
The decibel can be
expressed as:
decibel = 10 log(P / Pref
) (1)
where :
P = signal power (W)
Pref = reference power
(W)
A decibel is one-tenth
of a Bel - named after Alexander Graham Bell, the inventor of the telephone.
Note!
Doubling the signal level increases the decibel with 3 dB (10 log (2)).
If we know the decibel
value and the reference level, the absolute level can be calculated by
transforming (1) to:
P = Pref 10(decibel
/ 10) (2)
Example - Sound
Intensity and Decibel
The difference in sound
intensity of 10-8 watts/m2 and 10-4 watts/m2 (10,000
units) can be calculated in decibels as
ΔLI = 10 log( (10-4
watts/m2) / (10-12 watts/m2) ) - 10 log( ( 10-8
watts/m2) / ( 10-12 watts/m2) )
= 40 dB
Increasing the sound
intensity by a factor of :
- 10 raises its level by 10 dB
- 100 raises its level by 20 dB
- 1,000 raises its level by 30 dB
- 10,000 raises its level by 40 dB and so on
0 Response to "DECIBEL"
Post a Comment