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Three principles of power amplifier matching speakers

2021-05-07 41
When designing and installing a sound system, it is inevitable to encounter the problem of matching between the power amplifier and the speakers. From the artistic point of view, the matching of the power amplifier and the speakers should be warm and cold, soft and hard in terms of tone, and ultimately make the whole set of equipment restore the tone to be neutral. From a technical point of view, the following points should be paid attention to when connecting power amplifiers and speakers: power matching; impedance matching; damping coefficient matching. If we recognize the above three points when mating, the performance of the equipment used can be brought into full play.

Speaker
In order to make it able to withstand the impact of strong burst pulses in the program signal without damage or distortion.
Here is an empirical value for reference: the nominal rated power of the selected speaker should be more than 2 times the power obtained by theoretical calculation.

Power amplifier
Compared with the transistor power amplifier, the required regularity reserve is different from the tube power amplifier. This is because the overload curve of the tube amplifier is relatively flat. For the overcharged music signal peaks, the tube power amplifier does not obviously produce clipping, but only rounds the peaks of the peaks. This is what we often call flexible shear peaks. After the transistor power is placed at the overload point, the non-linear distortion increases rapidly, causing serious clipping of the signal. It does not round the peak but flatten it neatly. Someone used a composite impedance composed of resistance, inductance, and capacitance to simulate speakers, and tested the actual output capabilities of several high-quality transistor power amplifiers. The results show that when the load has a phase shift, there is a nominal 100W power amplifier, and the actual output power is only 5W when the distortion is 1%! Therefore, the selection of the reserve amount of the transistor power amplifier: high fidelity power amplifier: 10 Times, civilian high-end power amplifier: 6 to 7 times, civilian mid-range power amplifier: 3 to 4 times. The tube power amplifier can be much smaller than the above ratio. How much margin should be left for the average sound pressure level and the maximum sound pressure level of the system depends on the content of the program and the working environment. This redundancy is at least 10dB. For modern pop music, bungee music and other music, you need to leave 20-25dB redundancy, so that the sound system can work safely and stably.

Power matching

In order to meet the requirements of high-fidelity listening, the rated power should be determined according to the best listening sound pressure. We all have this feeling: when the volume is small, the sound is weak, thin, unable to come out dynamically, dull, the low frequency is significantly lacking, and the fullness is poor, and the sound seems to be shrinking inside and unable to come out. When the volume is right, the sound is natural, clear, round, soft, full, powerful, and dynamic. However, when the volume is too high, the sound is blunt, not soft, rough, and has the feeling of rooting in the ears. Therefore, the playback sound pressure level has a greater relationship with the sound quality. It is stipulated that the sound pressure level of the listening area should be 80~85dB (A weighting). We can calculate it from the distance from the listening area to the speaker and the characteristic sensitivity of the speaker. The rated power of the speaker and the rated power of the amplifier.


Three principles of power amplifier matching speakers


Impedance matching
The output of the power amplifier and the input impedance of the speakers should also be the same. Although there is some slight deviation between the two, it will not have a significant impact on the sound quality, but only has an effect on the output power of the amplifier, but it must be reminded that if the speaker input impedance is much lower than the output impedance of the amplifier, it will cause a significant increase in distortion , In severe cases, the power amplifier will be damaged. Therefore, it is better to choose the same as the two.

Matching of damping coefficient
The damping coefficient KD is defined as: KD= rated output impedance of the power amplifier (equal to the rated impedance of the speaker)/power amplifier output internal resistance. Since the internal resistance of the power amplifier output has actually become the resistance of the speaker, the KD value determines the amount of resistance experienced by the speaker. The larger the KD value, the heavier the resistance value. Of course, the higher the KD value of the power amplifier, the better. Too much KD value will make the speaker resistance too heavy, so that the pulse front settling time will increase and the transient response index will be reduced. Therefore, one-sided pursuit of a large KD value should not be one-sided when choosing a power amplifier. As a household high-fidelity power amplifier damping coefficient, there is an empirical value for reference. The minimum requirement: the KD value of transistor power amplifier is greater than or equal to 40, and the KD value of tube power amplifier is greater than or equal to 6.
What you need to know is that if the damping coefficient is too high, the sound from the speaker will be dry and not round; if it is low, the sound will tend to stick together. Therefore, when you configure the power amplifier, you should pay attention to the control of the damping coefficient of the stone machine between 30 and 40. The internal resistance of the amplifier is high, so be sure not to exceed 10.
Of these three principles, the most critical is the first point. Here we reiterate that the matching of amplifiers and speakers is better than a big horse-drawn car instead of a small horse-drawn car.
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