The matching principle between power amplifier and speaker

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The matching principle between power amplifier and speaker [Copy link]

In the application scope of Bluetooth and Wi-Fi audio, the following matching principles are mainly considered: power matching, impedance matching, frequency band matching, damping matching, and power reserve matching. The first two principles are the most important. Power matching. Some people often equate the rated power of the power amplifier with the rated input power of the speaker, and believe that power matching is only possible when these two power indicators are exactly the same. This view is one-sided, because the rated output power of the power amplifier and the rated input power of the speaker are two completely different concepts and should not be confused. The rated output power of the power amplifier refers to the power limited by distortion. If the output power level exceeds this level, the power amplifier output will produce clipping distortion, and a considerable dynamic margin must be left. The rated input power of the speaker refers to the limit power at which the speaker can work continuously for a specified time without damage. The national standard stipulates that the rated input power of the speaker refers to the limit power at which the speaker can work continuously for 100 hours without damage when the speaker is given the pink noise signal level of this power. If a low-power amplifier is used to drive a high-power speaker, the dynamic range of the amplifier is insufficient. When the speaker has not yet reached the required output sound pressure, the amplifier has already limited the distortion: 1. Using a low-power amplifier to drive a high-power speaker will result in "unable to push". Simply put, "unable to push" means that when the power is slightly higher, the distortion increases rapidly, and it is difficult to achieve full-band balance. 2. The continuous output power value of the amplifier is less than the continuous output power of the speaker, which is most likely to cause damage to the speaker. Because if the continuous output power of the amplifier is 100W, the continuous output power of the speaker is 200W. After connecting the system, once the volume knob is adjusted, when the output power is around 100W, the power amplifier is already in full load operation. The speaker still has a lot of margin. Once the user continues to increase the volume, the output power at this time exceeds the continuous output power value of the power amplifier, which is the moment when distortion begins. This distortion is called "clipping distortion" and is called "speaker killer" in the professional audio industry. This distorted signal can generate a DC-like electrical signal even if the power is very small, which can easily burn the speaker coil. For a speaker with a continuous output power of 200W, a 150W electrical signal with a distortion rate of 50% is more terrible than a 300W signal without distortion! On the contrary, if the input power of the speaker is too large, it will work continuously at the required output sound pressure level and will be easily burned. Therefore, the rated output power of the amplifier is generally required to be greater than the rated input power of the speaker. Impedance matching is ideal when the impedance of the amplifier is equal to the impedance of the speaker. At this time, the amplifier and the speaker are in good working condition, and the amplifier works in the best load line state, which can give the maximum undistorted power and obtain good sound effects. What if the impedance of the amplifier is less than the impedance of the speaker? For example, a 4Ω amplifier is connected to an 8Ω speaker? According to the power P=U*U/R, it can be calculated that the output power of the amplifier is only half of the rated power. At this time, the volume of the speaker feels relatively small, the sound pressure level is not enough, etc., but it will not cause damage to the equipment. Therefore, this configuration can be used in some cases, but it is not recommended. What will happen if an amplifier with an impedance of 8Ω is connected to a 4Ω speaker? At this time, since the actual connected load is only 4Ω, according to the power P=U*U/R, the current I at this time becomes about 1.4 times of the previous one. At this time, the power amplifier is in an overloaded state, which is likely to burn the power amplifier. Therefore, a high-impedance power amplifier must not be used to drive a low-impedance speaker. Band matching In order to obtain faster dynamic response and better high-frequency characteristics, the frequency band of the power amplifier should be quite wide. Usually, the electrical frequency response of the power amplifier is required to be flat, and its bandwidth should be much larger than the acoustic frequency response width of the speaker. The acoustic frequency response width of the speaker can only reach 20Hz-20KHz at most, while the electrical frequency response width of the power amplifier can reach 10Hz-100KHz.