Four moves to solve the problem of power amplifier for speakers
Power amplifier and sound box are equipped with appropriate cooling and heating, moderate hardness and hardness, so as to restore the tone of the whole set of equipment to be neutral, which is only from the artistic point of view. However, the technical considerations include: first, power matching, second, power Reserve matching, third, impedance matching, and fourth, the matching of damping coefficient is not difficult for the speaker to take power amplifier, this is the point. If we realize the above four points in the connection, the performance of the equipment used can be maximized and fully utilized. 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 the feeling that the volume is small, the sound is weak, thin, dynamic, dull, low frequency is significantly lacking, the fullness is poor, and the sound seems to shrink inside. When the volume is appropriate, the sound is natural, clear, round, soft, plump, powerful and dynamic. However, when the volume is too high, the sound is stiff, not soft, rough and has the feeling of sticking ears. Therefore, the replay sound pressure level has a great relationship with the sound quality, and the sound pressure level of the listening area is preferably 80 ~ 85dB (A rights calculation) We can calculate the rated power of the speaker and the rated power of the power amplifier from the distance from the listening area to the Speaker and the characteristic sensitivity of the speaker. Power Reserve matching, Speaker: in order to enable it to withstand the impact of the powerful pulse 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 theoretical calculated power. Power amplifier: compared with transistor power amplifier, electron tube power amplifier requires different power reserves. This is because the overcharge curve of the electron tube power amplifier is relatively flat. At the peak of overcharged music signals, the electron tube power amplifier does not obviously produce wave cutting, but only makes the tip of the peak round. This is what we often call flexible shear peaks. However, after the overload point, the nonlinear distortion of the transistor power amplifier increases rapidly, causing serious wave cutting on the signal. It does not round the peak but cuts it evenly. Some people use a composite impedance analog speaker composed of resistors, inductors and capacitors to test the actual output capability of several high-quality transistors power amplifier. The results show that when the load has phase shift, there is a power amplifier labeled 100 W, and the actual output power is only 5W when the distortion is 1%! Therefore, the selection of transistor power amplifier reserves: High Fidelity power amplifier: 10 times, civil high-end power amplifier: 6 ~ 7 times, civilian mid-range power amplifier: 3 ~ 4 times, while the electron tube power amplifier can be much smaller than the above ratio. How much margin should be left for the average sound pressure level and maximum sound pressure level of the system depends on the content and working environment of the program. This redundancy is at least 10dB, and for modern pop music, bungee jumping and other music, 20 ~ 25dB redundancy, so that the sound system can work safely and stably. Impedance matching, which refers to the rated output impedance of power amplifier, should be consistent with the rated impedance of the speaker. At this time, the power amplifier is in the optimal design load line state, so the maximum undistorted power can be given. If the rated impedance of the speaker is greater than the rated output impedance of the power amplifier, the actual output power of power 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 sound system can work, but the power amplifier is in danger of overload, requiring the power amplifier to have perfect overcurrent protection measures to solve the problem, for electron tube power amplifier, impedance matching requirements are stricter. Matching damping coefficient KD of damping coefficient is defined as: KD = power amplifier rated output impedance (Equal to the rated impedance of the speaker) /Power amplifier output internal resistance. Since the power amplifier output internal resistance has actually become the electrical damper of the Speaker, the KD value determines the amount of electrical damping the speaker is subjected. The larger the KD value, the heavier the electric damping. Of course, the larger the KD value of power amplifier, the better. If the KD value is too large, the electric damping of the speaker will be too heavy, thus increasing the establishment time of the pulse frontier, reduce transient response metrics. Therefore, when selecting power amplifier, we should not unilaterally pursue a large KD value. As a household high-fidelity power amplifier damping coefficient, there is an empirical value for reference. The minimum requirement is that the transistor power amplifier KD value is greater than or equal to 40, and the electron tube power amplifier KD value is greater than or equal to 6. To ensure the basic conditions of good steady-state and transient characteristics of playback, attention should be paid to the equivalent mechanical quality factors of sound boxes (Qm)With amplifier damping coefficient (KD) This kind of cooperation needs to consider the feeder of the speaker as part of the sound system as a whole. The equivalent resistance of the feeder of the Speaker should be small enough to be negligible compared with the rated impedance of the speaker. In fact, the power loss of the speaker feeder should be less than 0. 5dB (About 12%)This kind of cooperation can be achieved.