Amplifier with 4 elements
The configuration of audio equipment is very sophisticated, of which the configuration of power amplifiers and speakers is the most important. This article mainly introduces the main points of knowledge related to the matching of power amplifier speakers, power, power reserve, impedance, and damping coefficient. Amplifier speakers with 4 elements Power matching In order to meet the requirements of high-fidelity listening, the rated power should be determined based on the optimal listening sound pressure. We all have the feeling that the volume is small, the sound is weak, thin and dynamic, and there is no gloss, the low frequency is significantly lacking, and the fullness is poor. It seems that the sound cannot be contracted inside. When the volume is appropriate, the sound is natural, clear, round, soft and plump, powerful and dynamic. But when the volume is too high, the sound is stiff and not soft, rough, and feels ear-piercing. Therefore, the playback sound pressure level has a greater relationship with sound quality. The sound pressure level in the listening area is preferably 80 ~ 85dB (A weighted). We can calculate from the distance from the listening area to the speaker and the characteristic sensitivity of the speaker Speaker's rated power and power amplifier's rated power. Power reserve matching Speaker: In order to make it able to withstand the impact of burst strong 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 three times the theoretically calculated power. Amplifier: Compared with the transistor amplifier, the power reserve of the tube amplifier is different. This is because: the overload curve of the tube amplifier is relatively smooth. For the peak of the overloaded music signal, the tube amplifier does not obviously produce clipping, but only rounds the tip of the peak. This is what we often call flexible clipping. After the transistor amplifier is at the overload point, the non-linear distortion increases rapidly, which severely clips the signal. It does not round the peak but neatly cuts it. Some people use resistors, inductors, and capacitors to compound speakers to simulate the actual output capability of several high-quality transistor amplifiers. The results show that in the case of load 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 amplifier: 10 times Civil high-end power amplifier: 6 ~ 7 times Civil 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. The minimum amount of redundancy is 10dB. For modern pop music, bundi and other music, 20 ~ 25dB redundancy is required, so that the sound system can work safely and stably. Impedance matching It refers to the rated output impedance of the amplifier, which should be consistent with the rated impedance of the speaker. At this time, the amplifier is in the optimal design load line state, so it can give the maximum undistorted power. If the rated impedance of the speaker is greater than the rated output impedance of the amplifier, the actual output power of the amplifier will be less than the rated output power. If the rated impedance of the speaker is less than the rated output impedance of the power amplifier, the audio system can work, but the power amplifier has the risk of overload. It requires the power amplifier to have perfect overcurrent protection measures to solve it. The impedance matching requirements for the tube power amplifier are more stringent. Matching of damping coefficients The damping coefficient KD is defined as: KD = rated output impedance of the amplifier (equal to the rated impedance of the speaker) / internal resistance of the output of the amplifier. Because the internal resistance of the power amplifier output has actually become the resistance of the speaker, the KD value determines the resistance of the speaker. The larger the KD value, the heavier the resistance, of course, the larger the KD value of the power amplifier, the better. If the KD value is too large, the resistance of the speaker will be too heavy, so that the pulse leading time will increase and the transient response index will be reduced. Therefore, when choosing the power amplifier, one should not pursue a large KD value. As a household high-fidelity power amplifier damping coefficient, there is an empirical value for reference. The minimum requirements are: the KD value of the transistor power amplifier is greater than or equal to 40, and the KD value of the tube power amplifier is greater than or equal to 6. The basic conditions to ensure the stable and transient characteristics of the playback. Attention should be paid to the combination of the equivalent mechanical quality factor (Qm) of the speaker and the damping coefficient (KD) of the amplifier. This cooperation requires the speaker's feeder as the overall sound system. To consider. The speaker's equivalent resistance should be small enough to be negligible compared to the speaker's rated impedance. In fact, the power loss of the speaker feeder should be less than 0.5dB (about 12%) to achieve this coordination.