Simply put, decibel is the unit of amplifier gain. The ratio of the output of the amplifier to the input is the magnification, in units of "times", such as 10x amplifier, 100x amplifier. When using "decibel" as a unit, the magnification is called gain, which is a concept of two kinds of terms.
The conversion relationship between decibel and magnification in electricity is:
AV (dB) = 20lg (Vo / Vi)
AI(dB)=20lg(Io/Ii)
Ap(dB)=10lg(Po/Pi)
The formula for voltage (current) gain and power gain is different when decibel is defined, but we all know that the relationship between power and voltage and current is P=VV/R=IIR. After using this formula, the gain values ​​of the two are the same:
10lg(Po/Pi)=10lg(Vo.Vo/R)/(Vi.Vi/R)=20lg(Vo/Vi)
There are three main benefits to using decibels as a unit:
1) The value becomes smaller and the reading and writing is convenient
The total magnification of an electronic system is often several thousand, tens of thousands or even hundreds of thousands. A radio receives a signal from an antenna to a speaker output, which is about 20,000 times larger.
Decibel is used to first take a logarithm, and the value is much smaller.
2) Convenient operation
When the amplifier is cascaded, the total amplification is multiplied by the stages; when the unit is decibel, the total gain is added.
If a preamplifier is 100 times (20dB) and the latter is 20 times (13dB), the total power amplification is 100 & TImes; 20 = 2000 times, and the total gain is 20dB + 13dB = 33dB.
3) Conform to the sense of hearing, easy to estimate
The loudness of a person's hearing is positively related to the relative increase in power.
For example, when the electric power is increased from 0.1 watt to 1.1 watt, the sound heard is much louder; from 1 watt to 2 watts, the loudness is not too much; from 10 watts to 11 watts, there is no People can hear the difference in loudness.
If the absolute value of the power is expressed as 1 watt, and the gains are 10.4 dB, 3 dB, and 0.4 dB, respectively, this can more consistently reflect the difference in loudness heard by the human ear.
If you pay attention, you will find that the volume knob scale on the Hi-Fi amplifier is the standard decibel, which makes you intuitive when changing the volume.
In the decibel value, two points of -3dB and 0dB must be understood.
-3dB is also called the half power point or the cutoff frequency point. At this time, the power is half of the normal time, and the voltage or current is 1/2 of the normal time. In the electroacoustic system, the difference of ±3dB is considered not to affect the total characteristics, so various equipment indicators, such as frequency range, output level, etc., may have ±3dB in and out without explanation.
0dB means the output is as large as the input or the two comparison signals.
Decibel is a relative amount of quantity, there is no absolute magnitude. You can see how many dB of the measured value on the meter or the noise meter on the road, because people have set a benchmark for 0dB.
The commonly used 0dB benchmarks are as follows:
1) dBFS, with a full scale value of 0dB, is often used on various characteristic curves;
2) dBm, which produces 1mW power (or 0.775V voltage) of 0dB on a 600Ω load, which is commonly used on AC level measuring instruments;
3) dBV, 0 volts at 1 volt;
4) dBW, 0 dB at 1 watt.
After reading out how many dB, it is no longer necessary to turn into physical quantities such as voltage and sound pressure. Professionals can understand. Only in a few occasions, you have to fold it. You only need to substitute the formula:
10 A/20 (or A/10) power & TImes; D0 can be calculated.
among them,
A is the decibel value read;
D0 is the reference value when 0dB;
A/20 for voltage, current or sound pressure;
A/10 is used for electric power, sound power or sound intensity.
These machines are used for the production of nails
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