Old audio players know that the nominal power of a Japanese power amplifier is false, and its actual power does not reach its nominal power value. And many new players do not understand the truth, why Japanese power amplifiers can be virtual standard power, and its actual power is different from its virtual standard power?
I will discuss this issue for you today. Before we understand this problem, it is necessary to understand the correct meaning of some of the technical parameters related to this.
1, the difference between 6Ω and 8Ω?
We have all learned the power calculation formula: P = U2 / R. Simply put, power is equal to the square of the voltage divided by the resistance. From this formula we can see that the output power is inversely proportional to the load resistance. That is, the smaller the load impedance, the larger the output power of the same power amplifier.
Reflected in the definition, the rated output power refers to a sine wave fed at the input end under a certain load impedance (usually 8 Ω) and a certain harmonic distortion (according to 0.1% or 0.3% given by the manufacturer). The maximum power obtained by the signal at the output load is obtained using the formula P=U2/R.
It can be seen that when R=6Ω, the output power P at this time must be greater than the output power when R=8Ω. This is why it is said that the lower the impedance of the speaker, the harder it is to push.
2. What is the difference between 20Hz~20kHz and 1kHz?
Here we must briefly introduce the internationally accepted measurement standards for rated power:
In 1974, the Federal Trade Commission (also referred to as the FTC) specified how to measure the power rating of a power amplifier, driving an 8Ω speaker load in two channels, in the range of 20 to 20000 Hz. The effective wattage measured when the harmonic distortion is less than 1% is the output power of the amplifier, and the indicated power is the rated output power.
Why do you have to specify "20Hz~20kHz"? Here we use a very simple metaphor to illustrate: Suppose all the instruments included in a symphony orchestra can play automatically, but an amplifier is needed to power them. When all instruments work at the maximum volume without distortion, is the power more power-saving for a single violin, or is it more labor-saving to power all instruments? The answer is obvious.
Similarly, when the test signal is only a 1 kHz sinusoidal signal, the amplifier can save a lot of work compared to the wideband signal of 20 Hz to 20 kHz. In this regard, we can clearly see from the equal curve of the human ear.
Take the example of the loudness level of 10 squares. At a frequency of 1 kHz, the sound pressure can reach 10 dB, and at the frequency of 63 Hz, to achieve the same loudness level, the sound pressure should reach 40 dB. Because the human ear reacts more slowly to low frequencies than the intermediate frequency.
And we all know that for every 3dB increase in sound pressure, the output power will increase by a factor of two. It can also be seen that to achieve the same loudness level, the power consumption in the bass band is more.
This is why when the broadband measurement condition of 20 Hz to 20 kHz is used, the measured power output of the power amplifier is smaller than the output power when the measurement condition is only 1 kHz.
3. What is THD?
Before explaining THD, let's take an example.
Suppose there are two weightlifters A and B.
The maximum weight that A can lift normally is a 180Kg barbell, so it is easier to lift a 150Kg barbell, and the whole set of movements is not deformed, and it can hold up for 10 seconds.
B is worse, the maximum weight that can be lifted normally is 145Kg, and the old life can be lifted. It can also lift the barbell of 150Kg, but at this time, the waist, the arm, the push and other actions have been deformed, and at most It takes 3 seconds.
Well, although both of them raised the 150Kg barbell, we can't say that they both have the same "power", and it is obvious that B is taking longer and is more susceptible to "internal injury" because it has exceeded His range of abilities.
What does this example mean? A machine, like a human, must work within its capabilities, otherwise it will be abnormal and anomalies, we can call this phenomenon of abnormal work called "distortion".
Now let's take a look at what is THD.
THD is the abbreviation of Total Harmonic Distortion, which means "total harmonic distortion".
In general, the total harmonic distortion at the 1 kHz frequency is the smallest, so many electronic products use the distortion of this frequency as an indicator. This also involves the "1kHz" problem mentioned above.
Since total harmonic distortion is frequency dependent, the US Federal Trade Commission (FTC) stipulated in 1974 that total harmonic distortion must be measured in the full audio range of 20 Hz to 20 kHz. In addition, when measuring the rated output power of the power amplifier, it must be connected to a speaker with an impedance of 8 ohms and the total harmonic distortion is less than 1%. The total harmonic distortion is below 1%, which is generally not discernible by the ear. If it exceeds 10%, the distortion component can be clearly heard. The FTC also stipulates that the minimum requirements for total harmonic distortion are: 0.5% for the preamplifier and 0.7% for the combined amplifier, but in fact can be less than 0.1%: the FM stereo tuner is less than or equal to 1.5%, in fact Can be done below 0.5%; laser phonograph can achieve less than 0.01%.
It can be seen from this that when THD=10%, the measured power value is greater than the measured power value when THD=0.08%.
Because when THD=10%, it is equivalent to the weightlifter B raised a 160Kg barbell. Although it is lifted up, I am afraid it is subject to internal injuries, and the movement has been deformed.
4. What is JEITA and FTC?
JEITA: Japan Electronics and Information Technology Industries Association Japan Electronic Information Technology Industry Association FTC: Federal Trade Commission The US Federal Trade Commission FTC standard has been mentioned several times in the past, and its rated power rating is: 8 ohms, 20 Hz-20 kHz, THD<1%
The JEITA standard has a measurement condition of 6 ohms, 1 kHz, and THD = 10%. It is clear that the power measured under the JEITA standard is virtually high.
But this brings up a problem: the output power indicated by many official websites, especially the official website of Chinese, is measured according to the JEITA standard, so there is not much reference value.
5. How to judge the actual output power of a power amplifier?
In fact, it is very simple! Go to the official website to find the specifications of these amplifiers, there must be detailed, measured values ​​of the output power in accordance with the FTC standard. There is such a top: POWER CONSUMPTION means "total power consumption", which is a really meaningful indicator.
The parameters are in the case of Onkyo TX-NR809, the total power consumption in the manual is 710W, that is to say, when the seven channels work simultaneously, this amplifier can provide a total power consumption of up to 710W. It is only 100W per channel, and its official nominal peak power is 230W per channel, rated at 180W per channel, and this total power consumption should also be calculated as transformer efficiency, assuming 90% (actually difficult to achieve) 90%), audio and video processing circuit power consumption, as well as heat consumption, so that the power of each channel in the multi-channel state can not reach 90w per channel.
P3.5X6 Automotive Connector
P3.5X6 Automotive
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