The development history of audio technology can be divided into four stages: electron tube, transistor, integrated circuit and field effect tube. 1906, American deforest invented the vacuum triode, which pioneered the electro-acoustic technology of human beings. 1927 After Bell Laboratories invented negative feedback technology, the development of audio technology entered a new era. Representative amplifiers such as "Williamson" successfully applied negative feedback technology, which greatly reduced the distortion of the amplifier. In the 1950s, the development of tube amplifiers reached a climax, and various tube amplifiers emerged one after another. Electron tube power amplifier is still the first choice for enthusiasts because of its sweet and mellow tone. The appearance of transistors in the 1960s made audio enthusiasts enter a broader audio world. Transistor amplifier has the characteristics of exquisite tone, low distortion, wide frequency response and large dynamic range. In the early 1960s, the United States first introduced a new member of audio technology-integrated circuit. In the early 1970s, integrated circuits were gradually recognized by the audio industry because of their high quality, low price, small size and many functions. So far, 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 the field effect power tube has the pure thickness and sweet timbre of the electron tube, as well as the dynamic range of 90dB and the total harmonic distortion THD.

Introduce the specific meaning of dB. Unit dB is a relative unit widely used in electronics, which is used to measure and compare the power, voltage and current of a system. Later, due to the progress of science and technology, it was realized that human response to sound changed according to logarithmic law. So one unit said that Bell was the name of the inventor of the telephone. The expression is: Bel=lg(P/Po)P is the measured Power po is the reference power; Bel stands for logarithm based on 10. Actually, it is found that Bel is too big, so we take it as a new unit, that is, decibel (dB) divided by 10 is dB.

2. What is high fidelity? mFM^n7 %

What kind of audio equipment is Hi-Fi? Hi-Fi is the abbreviation of English High-Fidelity, which literally translates as "high fidelity", and its definition is: playback sound that is highly similar to the original sound. So what kind of audio equipment plays Hi-Fi? So far, it is difficult to draw a clear conclusion. Professionals in the audio industry use various instruments and means to detect various indicators to determine the Hi-Fi degree of equipment, while audio lovers often judge whether the equipment reaches their own Hi-Fi through their own ears. Judging the high fidelity of reproduced sound requires not only excellent equipment and software, but also a good listening environment. Therefore, there are differences between objective testing and subjective evaluation on how to correctly measure the high fidelity of audio equipment. 1 | ancient%

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

The performance of the overall technical indicators of the sound system depends on the performance of each unit. If the technical indicators of each unit in the system are high, then the overall technical indicators of the system are very good. Its technical indicators mainly include frequency response, signal-to-noise ratio, dynamic range, distortion, transient response, stereo separation and stereo balance. zOzQ ~ & amp

1. frequency response: the so-called frequency response refers to the frequency range of audio equipment when playing and the relationship between the amplitude and frequency of sound waves. Generally, this index is detected based on the frequency amplitude of 1000Hz, and the frequency amplitude is expressed by logarithm, and the unit is decibel (dB). Theoretically, the overall frequency response of the sound system is required to be 20~20000Hz. In practical use, it is often impossible to meet this requirement because of the circuit structure and the quality of components, but generally it must reach at least 32~ 18000Hz. & ltpyy7DsMu

Second, signal-to-noise ratio: OfJb* d

The so-called signal-to-noise ratio refers to the ratio between the reproduction of sound source software by the sound system and the new noise generated by the whole system, which mainly includes thermal noise, AC noise and mechanical noise. This index is generally expressed by the logarithmic ratio (dB) of the rated output power of the playback signal to the output power of the system noise when there is no signal input. The signal-to-noise ratio of general sound system should be above 85dB. k，CH； a

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

Dynamic range refers to the logarithmic value of the ratio of the maximum undistorted output power of the audio system to the noise output power of the static system when playing, and the unit is decibel (dB). The dynamic range of a sound system with good performance is above 100(dB). ? gzDD2#kk

4. Distortion: Distortion refers to some parts of the original audio signal (waveform, frequency, etc.). ) changed after the audio system played the audio signal. The distortion of the sound system mainly includes the following types: 1. Harmonic distortion: The so-called harmonic distortion means that the sound reproduced by the sound system has many additional harmonic components than the original signal source. This extra harmonic component signal is the frequency multiplication or frequency division of the signal source frequency, which is caused by the nonlinear characteristics of the negative feedback network or amplifier. The harmonic distortion of high fidelity system should be less than 65438 0%. 2. Intermodulation distortion: Intermodulation distortion is also a kind of nonlinear distortion. It mixes more than two frequency components in a certain proportion, and the frequency signals are modulated with each other. After passing through the playback device, a new nonlinear signal is generated, which includes a sum signal and a difference signal between each signal. 3. Transient distortion: Transient distortion, also known as transient response, is mainly due to the slow response of the amplifier when a large transient signal is suddenly added to the amplifier, thus distorting the signal. Generally, whether the envelope waveform of the amplifier output signal is similar to the input square wave waveform after the input square wave signal passes through the playback device indicates the amplifier's ability to follow the transient signal. 【Q- gq

Stereo separation: Stereo separation indicates the isolation between the left and right channels in a stereo system, and actually reflects the crosstalk between the left and right channels. If the crosstalk between the two channels is large, the stereoscopic impression of the reproduced sound will be weakened. K%{！ *t

Stereo balance of intransitive verbs: w.=BQ 1

Stereo balance represents the gain difference between the left and right channels in a stereo playback system. If the imbalance is too large, the sound image positioning of the reproduced stereo will be offset. Generally speaking, the stereo balance of a high-quality sound system should be less than 1dB. A 6-foot-tall box

4. How is the range and audio range of the sound reproduced by the sound system divided? What is the performance of each frequency band in music? Executive Director/Female

Generally speaking, the range of sound reproduction in a sound system can be divided into eight ranges: subwoofer, bass, midrange, alto, tenor, tenor, tenor and tenor. Generally, the audio frequency range can be divided into four frequency bands, namely, the low frequency band (30 ~150hz); In your frequency band (150 ~ 500 Hz); Medium and high frequency band (500 ~ 5000 Hz); High frequency band (5000 ~ 20000 Hz). Among them, 30~ 150Hz frequency band: can express the low-frequency components of music, so that viewers feel a strong sense of movement. 150~500Hz frequency band: it can express the expressive force of a single percussion instrument in music, and it is the part of low-frequency expression of strength. 500~5000Hz frequency band: it mainly shows the clarity of the singer's language and the expressive force of strings. 5000~20000Hz frequency band: mainly expresses the brightness of music, but too much will break the sound. Ip% eV r> v

5. What are the terms commonly used by audiophiles? b！ " fz}' o

The terms commonly used by audio lovers are abstract, and the common terms are as follows: 1. Nerve wire: mainly refers to the signal wire that transmits low level (millivolt, microvolt level) and small current. Generally used for audio and video, it is the meridian of God. The plugs at both ends of the advanced nerve wire are gold-plated RCA plugs, and the surface of the wire is coated with anti-static protective layer. 2. Heating wire: mainly refers to the speaker signal transmission line with large cross section and multiple strands. High-quality heating wire is made of oxygen-free copper and other materials. 3. Boiler: The so-called boiler is similar to the running-in period of mechanical machines, that is, after the audio equipment works for a certain period of time, the temperature inside the machine is the same as the ambient temperature, so that the working state of power amplifiers at all levels reaches the best point, and the sound reproduced at this time is the best. 4. Motorcycle: The so-called motorcycle comes from English Modify, which means to modify and decorate. Enthusiasts replace, transform and upgrade the components or circuits in the audio system, which is called motorcycle. 5. sonic boom: The so-called sonic boom refers to the deafening atmosphere produced when the music enters the climax when the audio equipment is replayed. 6. Gallbladder machine: Gallbladder machine refers to an amplifier made of electron tubes. The warm and transparent sound quality of electron tube power amplifier makes the older generation of enthusiasts unforgettable. 7. Stone machine: The so-called stone machine refers to an amplifier made of transistors. 8. Gallstone machine: that is, audio equipment made by mixing electronic tubes and transistors. Usually, electron tubes are used as preamplifiers and transistors are used as post-amplifiers. 9. Ring cow: The so-called ring cow refers to the ring transformer, which has smaller magnetic leakage than the ordinary transformer. 10. Large cell: Large cell refers to the power filter capacitor, which is generally a large-capacity capacitor above10000μ f. 1 1. Good sound: it means that the sound quality of audio equipment is very good, meeting the requirements of high fidelity. 12. Resolution: The reproduction of audio equipment has certain transparency, giving people the feeling of "crystal clear". 13. Dyeing: The so-called dyeing refers to the sound that is not in the playback sound due to the vibration of other objects or materials caused by sound wave vibration. It is harmful to the playback effect. 14. Microphone: refers to various microphones. 15. Supplement: refers to the high-quality components used in the transformation of the sound system. De **C34Si

6. How should the speakers be placed? ` _ q； h7n_？

The correct placement of speakers is one of the factors to obtain good playback effect. When placing speakers, we must pay attention to the following questions: 1. The distance between the two speakers should not be less than 1.5 ~ 2m and should be kept at the same level. The left and right sides of the speaker should be at the same distance from the wall. There should be no sundries in front of the speaker. . 2. The high-pitched unit of the speaker should be kept at the same horizontal line with the listener's ears, and the included angle between the listener and the two speakers should be 60 degrees, and a certain space should be left behind the listener. 3. The walls on both sides of the two speakers should be consistent acoustically, that is, the reflection of sound waves by the walls on both sides should be the same. 4. If the directivity of sound waves in the speakers is not wide, you can place the two speakers slightly inward. 5. For small speakers, if you feel that the low frequency is not enough, you can put the speaker near the corner. j！ C0(=

7. What should I pay attention to when connecting audio equipment? (S7r#@ 1

More importantly, connect audio devices at all levels. Improper connection will not only affect the playback effect of the device, but even damage the device. Eb n TX

A. basic requirements for equipment connection: a_lQS 9

(1) signal level matching: When connecting audio devices, we must pay attention to the difference of input and output signal levels between devices. If the input signal level of the previous equipment is too high, it will produce nonlinear distortion, otherwise it will reduce the signal-to-noise ratio of the playback system and even fail to drive the amplifier of the next equipment. Therefore, it should be noted that the level difference between devices should not be too large. If the signal level does not match in actual use, the input signal level must be lowered by the attenuation circuit or raised by the amplification circuit. For the general dynamic microphone, the output voltage is several millivolts, so it is necessary to set up a first-stage amplifier circuit to amplify the signal and send it to the preamplifier circuit. For recording stand, CD player and LD player, the output signal level is above 0.755~ 1V, which can be directly sent to the preamplifier. & lt8ROnjt

(2) Impedance matching: In Hi-Fi audio equipment, the output impedance of transistor power amplifier is low, while the output impedance of electron tube power amplifier is high. If they are connected to the loudspeaker with mismatched impedance, the output power of the amplifier will be unevenly distributed, or the transient characteristics of the loudspeaker will be deteriorated due to excessive damping. There are generally two kinds of impedance matching connections: balanced and unbalanced. The so-called balanced type means that the impedance of the signal transmitted by the two-core shielded wires to the ground is equal. The so-called unbalanced type means that one of the two-core shielded wires is grounded. When the balanced output is connected with the unbalanced input, it must be matched by adding a matching transformer. -5Nq|za

B. Connector connection mode: In Hi-Fi audio equipment, the connection of the equipment depends on various connectors, and the commonly used connectors are as follows. 4; %. Static plasma

(1) Dual-core plug: it is mainly used for transmitting signals between various devices and as an input plug for microphone input signals. According to its diameter, it can be divided into three types: 2.5mm, 3.5mm and 6.5 mm.

(2) Lotus plug: it is mainly used as the input and output plug of the line between audio equipment and video equipment. -RuHIo*Sho

(3) Canon plug (XLR): it is mainly used to connect the microphone and the power amplifier. ? :]: Hu

(4) Five-core socket (DIN): It is mainly used to connect the cassette recorder with the power amplifier, which can concentrate the stereo input and output signals on one socket. ~cb:^2(4&； '

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

(6)F and M plugs: mainly used for the input and output of RF signals in audio-visual equipment. & amphy eAV

8. What is the "OFC" hotline? What are the fever lines of "6N" and "7N"? /! A~_:gQ%

"OFC" is the abbreviation of "oxygen-free copper", which means "oxygen-free copper". As we all know, gold and silver in metals have the lowest resistivity and the best conductivity. However, if gold and silver are used as the material of heating wire, its price is very expensive, which is unacceptable to most enthusiasts. As a common metal material, copper has good conductivity and is widely used. However, copper contains many impurities, most of which are oxides, which affect its conductivity. What is the name of the one that is used more at present? Quot "OFC" line of "intelligent heating wire" adopts high-tech methods such as electrochemical method, PN junction injection method and isotope irradiation modification method to change the metal structure of copper, so that the surface of copper wire produces a unique metal structure, 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, so that high and low frequencies do not interfere with each other and are conducive to transmitting large signals. w#/O{v

"6N" and "7N" are used by enthusiasts to indicate the purity of heating wires made of oxygen-free copper. Because English "9" begins with the letter "n", for the convenience of expression, fans use "n" to represent "9", and the number before "n" indicates several "9". For example, "99.9999%" can be represented by "6N", which means its purity is six 9s. The greater the number before n, the higher the purity of the heating line.