What is the impedance of the audio in the home theater encyclopedia?

Impedance is the most commonly seen word in the sound circle, but what exactly does it mean? Many people will intuitively pick up the three-meter when they see that the impedance value of the horn is four or eight ohms. The two terminals of the speaker are a quantity to see if it is correct. Unfortunately, most people are disappointed, because the result of using the resistance meter on the three-meter is not marked with the speaker. Consistent. Why? Because you misunderstood, you made a mistake.

Impedance and resistance are not exactly the same thing. In physics textbooks, we first came into contact with the theory of electricity, which mentioned the principle and mathematical relationship between voltage, current, resistance and electrical power. Most of the people who have not continued to study electrical courses or those who are engaged in electronics majors have their lifelong knowledge of electricity. This is the glory that they did not do to sleep during the class, and they worked hard, earnestly and hard. The result, no wonder you will treat the impedance as a resistor.

The impedance is literally different from the resistance. Only one of the resistance words is the same, and the other is the word resistance. Simply put, the impedance is the resistance plus the reactance, so it is called the impedance. In a little bit, the impedance is the resistance. The sum of the capacitive reactance and the inductance reacted in the vector. In the world of direct current, the effect of an object on current obstruction is called resistance. All substances in the world have resistance, but the difference in resistance value. A substance with a small resistance is called a good conductor, and a substance with a large resistance is called a non-conductor. Recently, a superconductor called in the high-tech field is a thing whose resistance value is close to zero. However, in the field of alternating current, in addition to the resistance will block the current, the capacitance and inductance will also hinder the flow of current. This effect is called reactance, which means resisting the action of current. The reactances of capacitors and inductors are called capacitive reactance and inductive reactance, respectively, referred to as capacitive reactance and inductive reactance. Their unit of measurement is ohmic like the resistance, and the value of the value is related to the frequency of the alternating current. The higher the frequency, the smaller the capacitive reactance is, and the higher the frequency, the larger the capacitive reactance and the smaller the inductive reactance. In addition, the capacitive reactance and the inductive reactance also have a phase angle problem, and have a vector relationship, so it is said that the impedance is the sum of the resistance and the reactance in the vector.

In general, audio equipment is often referred to as the impedance of the speaker, the input impedance of the front and rear stage amplifier, the output impedance of the front stage, (the latter stage is usually not called the output impedance, but the output internal resistance), and the transmission impedance of the signal conductor. (or characteristic impedance), etc. If you talk about the internal circuit of the equipment and the impedance of the parts of the parts, it will be more complicated and complicated, and it can be clearly stated in a few words. Here we only briefly introduce the meaning of the impedance of the audio equipment.

Impedance tester

Start with the impedance of the horn. The most common horn impedance is eight ohms, and many are four ohms. What does this mean? This represents the sine wave signal of the 1KHz input when the horn is tested in the factory. It is four or eight ohms; or an average impedance value within the operating frequency response range of the horn. It may not be a fixed value, but it will vary with frequency, and may even be horrible. It may be as high as a dozen ohms at a certain frequency, or as low as one ohm or less at a certain frequency (this The horn is usually regarded as the killer of the latter stage, which was most famous in the past year. Ok, let's brainstorm; when the rear stage outputs a fixed voltage to the horn, according to Ohm's law, a four ohm horn will flow twice as much as an eight ohm horn, so if you calculate the power, You will understand why there is a rumor that an eight-ohm output of 100 watts of crystals will automatically change to two hundred watts when connected to a four-ohm speaker.

But don't be happy, don't be happy, think that it is cheap, there is no white lunch in the world. When the impedance value of the speaker drops all the way, the rear stage outputs a fixed voltage, and the current flowing through it will become bigger and bigger. You are sure of your Can the rear stage output such a large current? You know that the result of the speaker's impedance drop all the way to later is a bit like short-circuiting the speaker line, so the Apogee speaker with impedance value sometimes as low as one ohm is called the post-killer. The reason, you understand! All the post-amplifiers of the transistor, its output current capability has its design limits, beyond this range, the machine will burn. This is why people often say: the power of the latter stage is not large, but the output current is large, which seems to be the case (this issue will be discussed in detail later).

Similarly, if there is a pair of speakers with high impedance, like the early 15 RogersLS 3/5A, then the output power of the amplifier is not automatically halved? Yes! If the efficiency of the pair is very low, you want it. High-pitched sound can be used, can not use high-power amplifiers? Jianghu has rumors: Ups and Downs has a pair of 15 Rogers LS 3/5A in Zhongshan North Road, Taipei, for background music. The expansion machine that pushed it was an early Japanese Technics expansion machine, but many people praised it for its good news. What do you say? The early Japanese expansion machine gave the impression that the power rating is high, but the output current capability is impressive. Quite a whisper, can't you see a small set of bedside sound combinations that are 300W? But KRELL's 300W post-level you want to be alone. This high-voltage, low-current Japanese amplifier has a low-impedance horn that is now full of streets. It is soft at once, but if it hits a high-impedance horn, for example, it will become a name. In fact, when Harry meets Sally, the match is wonderful! You can wait and see. More home theater knowledge is available in the home theater network, official WeChat: cnhifi.