The development history of audio technology.

The development history of audio technology can be divided into four stages: electron tubes, transistors, integrated circuits, and field effect transistors. In 1906, American De Forest invented the vacuum triode, pioneering human electroacoustic technology. After Bell Labs invented negative feedback technology in 1927, the development of audio technology entered a new era. The more representative ones such as the "Williamson" amplifier successfully used negative feedback technology to reduce the distortion of the amplifier. Greatly reduced, the development of tube amplifiers reached a climax in the 1950s, and various tube amplifiers emerged in endlessly. Tube amplifiers are still preferred by audiophiles today because of their sweet and mellow tone. The emergence of the transistor in the 1960s brought audio enthusiasts into a broader audio world. Transistor amplifiers have the characteristics of delicate and moving timbre, low distortion, wide frequency response and dynamic range. In the early 1960s, the United States was the first to introduce a new member of audio technology - integrated circuits. By the early 1970s, integrated circuits were gradually recognized by the audio industry for their high quality, low price, small size, and multiple functions. Since its development, thick film audio integrated circuits and operational amplifier integrated circuits have been widely used in audio circuits. In the mid-1970s, Japan produced the first field-effect power tube. Because field effect power tubes have the characteristics of pure, sweet tone of electronic tubes, dynamic range of 90dB, and total harmonic distortion THD <0.01% (at 100kHz), they quickly became popular in the audio industry. Many amplifiers today use field effect transistors as the final output. The development of audio technology has gone through the historical periods of electron tubes, transistors, and field effect tubes, each with its own characteristics in different historical periods. It is expected that the mainstream development of audio technology in the future will be digital audio technology. 7/m7&b

Let me introduce the specific meaning of dB. The unit dB is a very widely used electronic unit. It is a relative unit for measuring and comparing the power, voltage and current of a system. Later, due to With the advancement of science and technology, we have realized that human response to sound changes according to the law of logarithm, so there is a unit called Bell (Bel), which is the name of the inventor of the telephone. Its expression is: Bel=lg(P/Po) P is the measured power and Po is the reference power: Bel represents the logarithm with base 10. In practice, it was found that Bel was too large, so one-tenth of it was taken as a new unit, which is decibel (dB). Divide Bel by 10. The dB expression is: dB=10lg(P/Po), dB=20lg(E/Eo), dB=20lg(I/Io). u= WyP

2. What is Hi-Fi? mFM^n7 %

What kind of audio equipment is Hi-Fi? Hi-Fi is the abbreviation of High-Fidelity in English, literally translated as "high fidelity". Its definition is: a playback sound that is highly similar to the original sound. So what kind of audio equipment reproduces sound that is Hi-Fi? It is still difficult to draw firm conclusions so far. Professionals in the audio industry use various instruments and various means to detect various indicators to determine the Hi-Fi level of the equipment, while audio enthusiasts often use their own ears to judge whether the equipment reaches the Hi-Fi level in their minds. . To judge the high-fidelity level of the reproduced sound, not only high-performance equipment and software are required, but also a good listening environment. Therefore, there is still a difference between objective testing and subjective evaluation on how to correctly measure the Hi-Fi level of audio equipment. A|Gu%

3. The main technical indicators of the sound system. <`rqsdT@H

The overall technical index performance of the audio system depends on the performance of each unit. If the technical index of each unit in the system is high, then the overall system The technical indicators are very good. There are six main technical indicators: frequency response, signal-to-noise ratio, dynamic range, distortion, transient response, stereo separation, and stereo balance. zOzQ~ &

1. Frequency response: The so-called frequency response refers to the frequency range when the audio equipment is played back and the relationship between the amplitude of the sound wave and the frequency. Generally, this indicator is measured with the frequency amplitude of 1000Hz as the reference, and the logarithm is used to express the frequency amplitude in decibels (dB). The overall frequency response of the sound system is theoretically required to be 20~20000Hz. In actual use, due to circuit structure, component quality and other reasons, this requirement is often not met, but generally it must reach at least 32~18000Hz.

2. Signal-to-noise ratio: OfJb* d

The so-called signal-to-noise ratio refers to the ratio of the reproduction sound of the audio system to the sound source software and the new noise generated by the entire system. The noise mainly includes thermal noise, AC noise, mechanical noise, etc. Generally, this indicator is expressed in decibels (dB) as the logarithmic ratio of the rated output power of the playback signal to the system noise output power when there is no signal input. The signal-to-noise ratio of a general audio system needs to be above 85dB.

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3. Dynamic range: "D#_@]z

Dynamic range refers to the maximum undistorted output power of the sound system during playback and the static system noise The logarithmic value of the output power ratio, in decibels (dB). Generally, the dynamic range of a sound system with good performance is above 100 (dB).

4. Distortion: Distortion refers to After the sound system replays the sound source signal, some parts of the original sound source signal (waveform, frequency, etc.) are changed. The distortion of the sound system mainly includes the following types: 1. Harmonic distortion: The so-called harmonic distortion. It means that the sound replayed by the sound system has many additional harmonic components than the original signal source. This additional harmonic component signal is the frequency multiplication or frequency division of the signal source frequency. It is caused by the negative feedback network or amplifier. Caused by linear characteristics. The harmonic distortion of the high-fidelity sound system should be less than 1%. Intermodulation distortion: Intermodulation distortion is also a kind of non-linear distortion, which is the mixing of two or more frequency components in a certain proportion. They modulate each other and produce a newly added nonlinear signal after passing through the playback equipment. This signal includes the sum and difference between the various signals. 3. Transient distortion: Transient distortion is also called transient response. The main reason is that when a large transient signal is suddenly added to the amplifier, the signal will be distorted due to the slow response of the amplifier. Generally, after the input square wave signal passes through the playback equipment, observe whether the envelope waveform of the amplifier output signal is correct. The square wave waveform is similar to express the amplifier's ability to follow transient signals [Q- gq

5. Stereo separation: Stereo separation represents the distance between the left and right channels in the stereo sound system. Isolation, which actually reflects the degree of crosstalk between the left and right channels. If the crosstalk between the two channels is large, the three-dimensional effect of the reproduced sound will be weakened. >

6. Stereo balance: w.=BQ1

Stereo balance represents the difference in gain between the left and right channels in the stereo playback system. If the imbalance is too large, the reproduced stereo sound The sound image positioning will produce a shift. Generally, the stereo balance of a high-quality sound system should be less than 1dB.

How are the sound range and audio range of the sound played back by the sound system divided? How do each frequency band perform for music? SV }eo/F

The sound range of the reproduced sound of the sound system can generally be divided into eight sound ranges: super bass, bass, mid-bass, mid-range, mid-treble, tenor, treble, and extra treble. The audio frequency range can generally be divided into four frequency bands, namely low frequency band (30~150Hz); mid-frequency band (150~500Hz); medium-high frequency band (500~5000Hz); high frequency band (5000~20000Hz). Among them, the 30~150Hz frequency band: can express the low-frequency components of music, making the listener feel a powerful sense of dynamics. 150~500Hz frequency band: It can express the expressiveness of a single percussion instrument in music, and is the part that expresses strength in low frequencies. 500~5000Hz frequency band: mainly expresses the clarity of the singer's language and the expressiveness of the strings. 5000~20000Hz frequency band: mainly expresses the brightness of music, but too much will cause the sound to break. ip%eV r>5

5． What are some common terms used by audiophiles. b!"fz}' o

The terms commonly used by audiophiles are relatively abstract, and the commonly used terms are as follows: 1. Nerve wire: mainly refers to the transmission of low level (millivolt, microvolt level), small current Signal cable. Generally, the nerve cable is used for both audio and video. The plugs at both ends of the higher-end nerve cable are gold-plated RCA plugs, and the surface of the wire is coated with an anti-static protective layer. 2. Fever cable: mainly refers to the larger cross-section. , Speaker signal transmission lines with a larger number of strands. High-quality fever cables are made of oxygen-free copper and other materials. 3. The so-called burn-in period is similar to the friction period of mechanical machines, which means that the audio equipment will work to a certain extent. After a certain amount of time, the temperature inside the machine is the same as the ambient temperature, so that the working conditions of the amplifiers at all levels reach the optimal point, and the sound reproduced at this time is the best. 4. Modify: The so-called Modify comes from the English word Modify. Modification and modification. Audiophiles replace and modify components or circuits in the audio system to upgrade it, which is called bursting: The so-called bursting refers to the sound when the music reaches its climax during playback. The deafening atmosphere produced. 6. Tube amplifiers refer to amplifiers made of tubes. The warm and transparent sound quality of tube amplifiers is still unforgettable by the older generation of audiophiles. 7. Stone amplifiers refer to those made of transistors. 8. Gallstone amplifier: It is an audio equipment made by mixing tubes and transistors. Generally, the tube is used as the pre-amplifier and the transistor is used as the post-amplifier. The so-called ring ox is a toroidal transformer. Compared with magnetic leakage, 10. Large water pond refers to the power supply filter capacitor, which is generally a large-capacity capacitor of more than 10000 μF. 11. Beautiful sound: refers to the sound quality of the audio equipment, which reaches high security. Real requirement. 12. Resolution: Refers to the sound reproduction of the audio equipment having a certain degree of transparency, giving people a "clear" feeling.

13． Dyeing: The so-called dyeing refers to the sound that is not in the playback sound due to the vibration of sound waves causing other objects or materials to vibrate during the playback process. Its effect on replay is detrimental. 14. Microphone: refers to various microphones. 15． Supplements: Refers to higher quality components used when modifying a sound system. de**C34Si

6． How should speakers be placed? `_q;h7n_?

The correct placement of the speakers is one of the factors to obtain good sound playback effects. The following issues must be paid attention to when placing them: 1. The distance between the two speakers should be no less than 1.5~2 meters and should be kept at the same level. The left and right sides of the speaker should be the same distance from the wall. There should be no clutter in front of the speaker. . 2. The tweeter unit of the speaker should be at the same level as the listener's ears. There should be a 60-degree angle between the listener and the two speakers. There should be a certain amount of space behind the listener. 3. The walls on both sides of the two speakers should be acoustically consistent, that is, the walls on both sides should reflect sound waves the same way. 4. If the directivity of the sound waves of the speakers is not wide, the two speakers can be placed slightly inward. 5. For small speakers, if you feel that the low frequency is not enough, you can place the speaker close to the corner. J!C0(=

7. What issues should be paid attention to when connecting audio equipment? (S7r#@1

The matching between all levels of audio equipment is more important. If connected Improper use will not only affect the playback effect of the equipment, but may even damage the equipment.

A. Basic requirements for equipment connection: a_lQS 9

(1) Matching of signal levels. : When connecting audio equipment, be sure to pay attention to the difference in input and output signal levels between each equipment. If the input signal level of the front-end equipment is too large, non-linear distortion will occur, otherwise it will degrade the playback system. The signal-to-noise ratio cannot even drive the amplifier of the next-level equipment. Therefore, when patching, pay attention to the fact that the level between the equipment should not be too different. If the signal level does not match in actual use, attenuation must be used. The circuit reduces the input signal level, or increases the input signal level through the amplifier circuit. For a general dynamic microphone, the output voltage is several millivolts, so a first-level amplifier circuit is required to amplify the signal and send it to the front. Amplification circuit. For recording decks, CD players and LD players, since the output signal level is above 0.755~1V, it can be directly sent to the preamplifier. <8ROnjt

(2) Impedance matching. : In Hi-Fi audio equipment, the output impedance of transistor power amplifiers is low, while the output impedance of tube power amplifiers and other equipment is high impedance. If the impedance does not match when they are connected to the speaker, the output power of the amplifier will be distributed. Uneven, or the transient characteristics of the speaker are deteriorated due to excessive damping. There are generally two types of impedance matching connections. The so-called balanced type means that the impedance of the two-core shielded wires that transmit the signal is equal to the ground. Unbalanced type means that one of the two-core shielded wires is connected to the ground. When the balanced output is connected to the unbalanced input, a matching transformer must be added for matching.

B. Connection method: In Hi-Fi audio equipment, the connection of the equipment is completed by various connectors. The commonly used connectors are as follows 4;%.qP

(1) 2. Core plug: It is mainly used to transmit signals between various equipment and as an input plug for microphone input signals. It is divided into three types according to its diameter: 2.5mm, 3.5mm, and 6.5mm. 08EOS VK

（ 2) Lotus plug: mainly used for input and output plugs between audio equipment and video equipment. -RuHIo*Sho

(3) XLR plug: mainly used for microphones and amplifiers. ?:]:hU

(4) Five-core socket (DIN): Mainly used for the connection between the cassette recorder and the amplifier, it can concentrate the stereo input and output signals On a socket. ~cB:^2(4&'

(5) RCA plug: RCA plug is mainly used for the transmission of video signals in equipment. t/Ox{[9&F

(6) F, M plug: It is mainly used for the input and output of radio frequency signals in audio-visual equipment. &hy eAV

8. What is "OFC" fever cable? What are "6N" and "7N" fever cables? /!A~_:gQ%

"OFC" is the abbreviation of "Oxygen Free Copper" in English, which means "oxygen-free copper". As we all know, gold and silver have the smallest resistivity and the best electrical conductivity among metals. However, if gold or silver is used as the material for making fever wires, the price is very expensive and not acceptable to most enthusiasts. As a commonly used metal material, copper has good electrical conductivity and is commonly used. However, because copper contains many impurities, most of which are oxides, it affects copper's electrical conductivity.

At present, the most commonly used "OFC" line, which is called "intelligent fever line", uses high-tech methods such as electrochemical method, PN junction implantation method, and isotope irradiation modification method to change the properties of copper. The metal structure creates a unique metal structure on the surface of the copper wire, making the surface of the same copper wire suitable for transmitting frequency signals above 5000Hz, while its center is only suitable for transmitting frequency signals below 5000Hz, thus making high and low frequencies incompatible with each other. Interference is beneficial to improving the clarity of the playback sound and improving the sound quality when transmitting large signals. w#/O{v

"6N" and "7N" are used by audiophiles to indicate the use of no interference. The purity of the fever wire made of oxygen copper material. Because the beginning of the English "9" is the letter "N", for the convenience of expression, enthusiasts use "N" to represent "9", and the number in front of "N" indicates the number. "9". For example, "99.9999%" can be represented by "6N", which means that its purity is six 9s. The larger the number in front of N, the higher the purity of the fever line.