The structure and basic knowledge of car audio system

1. Host (audio source)

From a professional point of view, the host should be defined as a sound source, which converts the magnetic signal or digital signal of the music software into corresponding electrical signals.It is installed incarOn the console. It is the core of any sound system. It is also an important part of the sound system. The mainframe has undergone tremendous changes in its function and quality since its development from AM radio to cassette deck. Now the host is becoming more and more multifunctional.

Classification of hosts: There are many types of hosts. We divide the signal source into the following categories:

1. AM/FM frequency modulator: used to receive radio frequency modulation and amplitude modulation signals, and has now developed into a digital frequency modulator.

2. Cassette deck: also known as cassette player, used to play tapes, but the sound quality is poor.

3. CD player: The signal-to-noise ratio and sound quality of the music signal are good, and it is an ideal sound source, but the capacity is small.

4. VCD player: The product of digital audio compression technology MPEG-1, which can play video and audio, but the sound quality is poor.

5. DVD player: using MPEG-2 as the video digital circuit module, and AC-3 as the audio signal decoding power module, high-performance interpretation of audio and video.

6. MD player: It is a thin DISC of floppy disk, the main feature is that it is smaller than CD, the sound quality is good, and it can record.

7. MP3 player: large capacity, one disc can store more than one hundred songs, and the sound quality is good.

8. Hard disk playback: You can download music directly from the network for playback, and you can record music repeatedly.

Among the above various signal sources, sound quality is the goal. Currently, CD is the most ideal, but its shortcoming is that it has a small capacity and can record more than ten pieces of music at most on a single disc, and it cannot be recorded repeatedly. The sound quality of MD is better than that of CD, and it can be recorded freely. The disc will not be worn due to the protection of the shell, but the disc source is less.

(Note: Classification of fever type and ordinary type host)

Generally, fever-type mainframes are pure audio sources, without power amplifiers, with high grades and good sound quality. A host that can only be used with other power amplifiers when in use. Also commonly known as "dumb machine". Because it saves the cost of other components and greatly reduces the "heat transmission", the fever-type mainframe is of great help to the improvement of sound quality, and the type of mainframe should be considered first in the pursuit of excellent sound quality. Ordinary mainframes generally have built-in four-way power amplifiers, the power ranges from 40W-60W per channel, and the RMS (rated) power is about 10-15W.

The specifications of the host: The host is divided into two specifications, 1-DIN and 2-DIN. (2-DIN custom support large screen machine type double layer is called).

Mainly according to the vehicle installation position (installation space of the center console). Cars suitable for installation of 1-DIN models are: Jetta, Santana, Mitsubishi, Audi, Sonata, etc. Cars suitable for installation of 2-DIN models are: Toyota, Honda, Buick, Passat, Nissan, Skoda (Europe) Ya) etc.

Note: if it isBMWX5,BenzS-600, Audi A6L, A4, Toyota Reiz,Mazda6. Honda 2.4, the type of car needs special attention. Because the center console of this type of car is not a standard DIN design, when installing the host, a specially made host mold is required for stable installation.

2. The main parameters of the host (performance indicators)

The most intuitive thing about the quality of a host is to look at its technical parameters.

There are mainly the following aspects.
1. Output power: Most of the power marked by the current host is the peak power, which is between 40-60W. The larger the better, usually the host with too small output power needs a dedicated power amplifier (generally, the rated power is between 10-15W.

2. Frequency response (HZ): The frequency range that the human ear can hear is 20HZ-20KHZ, so the index must reach this value at least, and the wider the better, (the lower the lower limit frequency, the larger the upper limit frequency, the better) .

3. Signal-to-noise ratio (S/N): refers to the ratio of music signal to noise, in decibels (DB). The larger the value, the better. Generally, high-end hosts are below 100DB, and the sound is clean and clear.

4. Point harmonic distortion (THD): This indicator reflects the percentage of the reproduction degree of sound reproduction. The smaller the value, the better. Generally, the point harmonic distortion of high-end inspection products is below 1%.

5. RCA output channels/voltage: Most hosts have 1 set of RCA outputs, which can output low-voltage signals, so that they can be directly transmitted from the host to the external power amplifier. The host usually has 1-3 pairs of RCA outputs. Of course, the more the better, the frequency division will be more detailed. Moreover, the RCA voltage is generally between 2V-6V. Generally, the RCA voltage of a high-end host can reach 4V-6V. Choosing a higher voltage will greatly help the improvement of the system.

Three, the function selection of the host

Due to the specific listening space of the car, it has a certain impact on the sound field and sound quality. In order to solve these problems, the current host has a response function and strives to achieve the effect of on-site listening.

1. RDS display function: You can display the information sent by the radio on the display of the host (you can't hear it but you can see it).

2. Loudness adjustment function (LOUND): When the volume is low, it is used to compensate high frequency and low frequency. Usually when the volume is low, we will find that the treble and bass seem to be gone, and the entire sound does not seem to have a sense of hierarchy. At this time, as long as the LOUND function is turned on, the host will boost the treble and mid-bass, so that you can hear fullness, Clear voice.

3. Preset storage: store the frequency of your selected radio station in the host memory.

4. Preset scan: It is to scan your preset radio frequency band or song music one by one for a few seconds to select your favorite radio station song music.

5. Channel adjustment (BAL/FAD): used to adjust the balance of the left and right sound fields and the front and rear sound fields.

6. Mute function (MULE): quickly lower the volume.

7. Preset equalization mode: This function mainly sets different frequency response curves for different types of music. ROCK, POP, JAZZ, VOCAL, CLUB, NEWAGE, CLASSLC.

8. Contrast adjustment: you can change the brightness of the screen light according to your preferences.

9. Wake-up function: Press any button on the host to wake up the host and let it start working.

10. Anti-theft function: For example, the front panel of the host can be removed; hide the panel; set a password; or use a security card to prevent the host from being stolen.

EQ (Equalizer, Equalizer, crossover)
EQ is an audio signal processing equipment that can control the signal strength of different audio points (segments). Due to the narrow and irregular interior space of the car, various interior materials and panels absorb and reflect sound, soCar stereoThe sound spectrum reproduced by the system is very uneven, that is, the spectrum curve is not smooth enough, which requires an equalizer to make up for the deficiencies of the sound system.

1. The type of equalizer:

A. Graphic equalizer. This type of equalizer can only adjust the amplitude at a fixed center frequency and bandwidth. It usually controls some sliding potentiometers. The "graphics" formed by the potentiometers are just like the frequency response curve. Implement an equalizer.

B. Parametric equalizer: This type of equalizer can adjust the existing equalization parameters, amplitude, frequency, width, etc. It is generally used in the audio system of competition vehicles or audiophiles. The price is more expensive and requires professional debugging.

C. Digital equalizer, DSP (digital signal processing), can edit the rate of all unused frequency bands, and store them in the memory to form music styles such as rock, blues, symphony, vocals, etc., the best equalizer A kind of attracting professionals.

2. The main parameters of the equalizer:

A. Signal-to-noise ratio;

B. Total harmonic distortion;

C. Frequency response;

D. Maximum input and output level;

E. Input gain;

F, PFM frequency;

G. Input the number of negligent channels (RCA);

H. Input and output impedance;

I. Equalizer center frequency;

J. Balanced input noise suppression;

K. Input/output impedance;

3. The function of the equalizer:

A. Correct the frequency distortion generated by audio equipment to obtain a flat response;

B. Improve clarity and naturalness;

C. Improve the unevenness of production in the car and ensure its frequency characteristics are flat.

Why is it necessary to introduce equalizer and crossover at the same time in this chapter, because many people will mix equalizer and crossover in a sound system, resulting in a misunderstanding of use and preventing a good system from taking advantage of its advantages. So let's understand the crossover together.

A crossover is an electrical appliance that inputs specific audio to the speaker in order to get the best reproduction of the sound. For audio systems that use separate speakers, it is best to use a crossover, which can not only improve the sound quality but also protect the tweeter.

Crossovers are divided into two categories: A: power crossover (passive crossover) B: electronic crossover (active crossover)

Power divider: divides the frequency after the power amplifier, it is through the inductancecapacitanceresistanceThe filter network composed of passive components transmits the audio signals of each frequency band to the speakers of the corresponding frequency band for reproduction. The advantages of the power divider are low cost, simple structure, easy adjustment, and strong adaptability. The disadvantages are , The insertion loss is large, the efficiency is low, the transient characteristics are poor, and it does not have the amplification effect, it is difficult to connect the wide frequency response of the audio signal and the good connection of the crossover point.
Electronic crossover is also called active crossover: It is composed of various resistance-capacitance components and transistor-type integrated circuits and other active devices. It is an analog electronic filter between the host and the power amplifier, which can switch the host After the output audio signal is divided into different frequency bands, it is amplified in the input power amplifier. The advantage of the electronic crossover is that it has a certain amplification ability, the frequency spectrum of each frequency band is balanced, mutual interference is small, the output dynamic range is large, and the power amplifier can be reduced. The disadvantage of intermodulation distortion is that each frequency band requires a separate power amplifier circuit.

Equalizers and crossovers are indispensable important equipment in most high car audio systems, especially in car competitions, which can play an important role.

Detailed explanation of electronic crossover/EQ function and use:

The abbreviation of EQUALZER, also known as equalizer, equalizer, in the audio world, it is widely used, but many people misuse it. Produced unsatisfactory results. To use the equalizer well, we must first understand the most basic thing in music, that is, frequency (see the appendix for the frequency division of various music). Only when you really know it and make friends with it, you can do whatever you want. The use of equalizer. (Understanding the various frequency ranges is the basis)

There is a very close relationship between the frequency range and the listener:

The ultra-low frequency range is 1HZ-20HZ. This frequency band should not be heard by human ears. If their energy is very large, we can feel the feeling of pressure. Pipe organs and earthquakes can generate these frequencies. The extremely low frequency range is 20HZ-40HZ. Most of the sounds in this frequency band are drums, pianos, electronic organs (bass), cellos or electric basses, which are the basis of music. The mid-low frequency range is 50HZ-315HZ. This octave is usually referred to as the range of bass or accent, and appears in the low frequency part of the middle vocal. Or horns, clarinets, and flutes also have the performance of this frequency band.

In the mid-frequency range of 315HZ-3200, the human ear can easily hear this frequency band. In fact, if we listen to this frequency band alone, its sound quality is like the sound heard in life. It is necessary to increase the low frequency and high frequency to be pleasant to the ear.

The medium and high frequency range is 3200HZ-6000HZ. The human body is particularly sensitive to this interval frequency band. The clarity and transparency of the sound are all affected by this frequency band. The horn speaker used in public broadcasting is designed to play the frequency of 3500HZ. The overtone of the human voice will also be affected. Appears in this frequency band.

The high frequency range is 6KHZ-12KHZ, this frequency band can make music brighter, but they will only account for a small part of the music, this range of high frequencies such as dental, labial and tongue.

The ultra-high frequency range is 12KHZ-20KHZ, which is the highest pitch in the music frequency range. Only very high pitches can reach this range, and if this frequency has a great influence on the characteristics of the music itself, the sound will be different. reality.

If we can't tune the sound of various vocals and instruments with an equalizer, it is possible that we have selected the wrong frequency, and the result of our boost and attenuation is not aimed at the energy of the main vocals and instruments. Of course, the more tuned, the worse, so We must understand the relationship between music and frequency. To put it bluntly, an equalizer is the volume of a specific frequency.switch.

In terms of car audio equipment matching, the car audio system already has the basic systems of the host, power amplifier, and speakers. If you want to improve the sound quality of the entire system and adjust more delicately, and make the music playback more complete, it must be in the audio system. Add EQ (equalizer) to correct the defects of the space sound characteristics and speaker amplitude-frequency characteristics in the car, or to polish the sound, you can adjust the position of the speakers in the car and adjust the front, back, left, and right to suit personal hobbies and enhance the sense of ready-made.

In recent years,

Many brands of car audio such as: Alpine, Pioneer, Kenwood, JVC, etc., in order to achieve better sound quality, some frequency compensation EQs that can produce special effects are set in the main unit, and a variety of tuning modes are preset to create a play It does not require the sound effects of music, and provides a good sound environment. Even if it is not professional knowledge, it will not make the sound field tuned. Just press the preset button to achieve the preset effect, such as ROCK (rock music) VOCAL (singing) CLUB ( Club) NEW-AGE (avant-garde) POP (pop music) JAZZ (jazz) CLASSI (classical music), etc., the sound source is frequency compensated, and the principle of tuning is not to affect the loudness of its melody performance, even when the volume is large, It can't make people feel uncomfortable, and the best sound environment can be combined according to people's preferences.

Note: Although EQ (equalizer) can change the frequency of vocals and musical instruments and the sound effects of the listening environment, excessive use will make the sound strange. When we increase a certain frequency, in fact, we let the frequency of a certain frequency If the volume is loud, it may be distorted, so we must use it carefully. EQ is a good helper, and also an expert at screwing you up. Spend more time to understand the frequency characteristics of various instruments and vocals, and spend more time to familiarize yourself with the functions of EQ. Try again if you make a mistake, only if you have the courage to try, can you do better).

4. Power amplifier (abbreviated as power amplifier)

The power amplifier is a kind of signal working and amplifying power. In professional audio, in order to ensure that there is enough power to drive the speaker, a professional power amplifier must be installed between the host and the speaker. The requirement for the power amplifier is that the output power may be large. The power should be high and the distortion should be small.

Classification of power amplifiers:

1. According to the equipment used by the power amplifier:

A. Electronic tube amplifier: commonly known as "tube amplifier", using electronic tubes as amplifiers, the main advantage is: large dynamic range. Good linearity, beautiful timbre, sweet and docile, suitable for playing classical music. The shortcomings of the tube power amplifier are that the internal resistance is large, which leads to a small damping coefficient of the amplifier, which affects the transient characteristics. The second is that the tube power amplifier needs high-voltage power supply, which cannot be separated from the transformer. The harsh operating environment (high temperature, vibration, power supply, etc.) has greatly restricted the use of tube amplifiers in car audio systems, so they are often not popular.

B. Transistor amplifier: It overcomes the two shortcomings of tube amplifiers. One is that the damping coefficient can be made very high, and it has good transient characteristics. It is brighter, brighter and more powerful than tube amplifiers in terms of rhythm and strength. Suitable for playing current music. The second is that no transformer is needed, which not only saves costs and reduces the volume but also avoids distortion caused by transformers. Transistor amplifiers are the mainstream products that are often used in car audio amplifiers nowadays. They have a wide variety and complete grades and are the main products used by lost car owners.

C. Integrated circuit amplifier: Its most prominent feature is high reliability, simple peripheral circuit, easy assembly, and its shortcomings are temporary acoustic indicators (power, frequency response, distortion, signal-to-noise ratio, etc.) and sound quality are not as good as discrete The amplifier composed of components is mainly used in the power amplifier level in the host.

2. Classified by circuit working status:

A. Class A amplifier: The working principle of this kind of power amplifier is that the output device (transistor or tube) always works in the linear part of the transmission characteristic curve. After the input signal has a continuous current flow for the output device throughout the entire cycle, the distortion of this amplifier is small. , But the efficiency is about 50% low, and the power loss is large. Generally, there are more high-end machines suitable for home use.

B. Class amplifier: Two kinds of transistors work alternately, each transistor is turned on in half a cycle of the signal, and turned off in two half cycles. The efficiency of this machine is about 78%, but the shortcomings are prone to distortion (two Distortion that occurs when the transistors are turned on separately).
C. Class A and Class B amplifiers: Class A amplifiers have the advantages of good sound quality and high efficiency of Class B amplifiers. They are widely used in home, professional, and car audio systems.

3. Classification of amplifier functions:

A. Pre-amplifier: The main purpose is to perform necessary processing and voltage amplification on the signal transmitted by the signal source, and then output it to the post-amplifier.

B post-amplifier: Amplify the signal sent by the pre-amp without distortion, and drive the speaker system with enhanced power. In addition to the amplifying circuit, various protection circuits are also designed. Such as short-circuit protection, over-voltage protection, over-heat protection, over-current protection, etc., the pre-stage power amplifier and the post-stage power amplifier are generally only used in high-end machines or professional occasions.

C. Combined amplifier: Combine the pre-amplifier and the post-amplifier into one power amplifier, and merge the functions of the former two. Generally speaking, the amplifiers are combined and lost and have a wide range of applications.

The main function of the power amplifier:

1. Electronic crossover: There are three options for this function: FULL (full tone) HP (high pass)-only let the crossover point such as (80HZ) above the frequency to pass, this setting is mainly used for middle and high pitch speakers. LP (low pass)-only let the frequency below the crossover point (80HZ) pass. This setting is mainly used for woofers, some of which also set crossover adjustable. The frequency division can be set by dividing points according to different system designs. (Some are only fixed at the frequency points of 80HZ-100HZ-120HZ).

2. Signal input selection: There are two input modes: RCA signal (low voltage signal) and host speaker wire (high voltage signal). To obtain good sound quality, RCA signal input can be used. If the host has no RCA signal or the original host is retained, the only choice is to use high-level input (commonly known as high to low).

in addition. Many power amplifier products have one or two sets of signal output, which can pass the signal to another power amplifier. This not only saves the cost of the crossover, but also guarantees excellent sound quality. The methods used are different, and some processing methods will make the sound quality worse.

3. Input gain adjustment: It is used to adjust the input voltage of the power amplifier and the signal voltage of the urgent output to achieve the most ideal matching state to ensure that the sound will not be distorted.

4. Bridge output: When the power amplifier adopts the bridge connection method, the output power can generally be doubled, so that it can be used as a queen when needed (such as used to drive the subwoofer).

5. Tone adjustment: there are bass and treble adjustments. The boost attenuation can be carried out at two frequencies of 45HZ-10KHZ, and the adjustment range is as early as 0DB-12DB. The bass that can be played separately is more full and deep, and the treble is more clear and transparent.

3. The main parameters of the output amplifier:

1. Frequency response capability: The frequency response range is 20HZ-80KHZ, and the frequency response of the speaker from bass to treble requires a frequency response of 20HZ-20KHZ. As the bottleneck component of signal transmission, the power amplifier requires a wider frequency response. For example, 7HZ-80KHZ, the signal integrity can only be ensured by a few times.

2. Signal-to-noise ratio: This is the parameter that most directly reflects the quality of the power amplifier, generally above 80DB, and high-quality products often reach above 105DB. If you are pursuing the purity of sound quality, that value cannot be ignored.

3. Distortion: This combination of two other important indicators of the power amplifier.

"Rated power (RMS)" and maximum power (Peakpower) are discussed together. When a power amplifier works at its rated power, the distortion should be relatively small, generally reaching the range of 0.5%—0.01%. When the maximum power or bridge is early, the signal may be Produce distortion, clipping (incomplete waveform signal) and other distortions. The ratio of distortion will also increase, about 0.5%-1% is normal, the smaller the ratio of distortion, the better the sound effect, which is also an important indicator of power amplifier.
4. Sensitivity: It is a kind of adjustment level, the range is from 100MV-6V or even more, and the tuning must match the sound source.

5. Load capacity: Household power amplifiers are generally 8Ω/4Ω and car power amplifiers are 4Ω/2Ω. However, the impedance of individual power amplifiers can be as low as 0.1 ohms, and the ability is extraordinary. At this time, a power amplifier can connect dozens of woofers in parallel to create an ideal sound level. The sound pressure refers to the pressure of the sound on the human ear. It is a measure of the ability of a sound system, because the higher the sound, the higher the system requirements, because the highest record is 169.0DB in China and 176.5DB in foreign countries. Just like the dozens of woofers in the car, the glass is broken, but this scene is probably only seen when you love to race.

6. Working voltage: Car audio generally works normally in the range of 10V-15V.

7. Damping coefficient: This readme is calculated from the output impedance of the rated load (4Ω). It is generally believed that the smaller the output impedance and the higher the damping coefficient, the better the power amplifier. In fact, the ratio of high-quality power amplifiers is above 50, and some even Exceed. Although some experts believe that a damping coefficient of about 50 is sufficient. The higher the coefficient, the wire requirements can be loaned. Relatively, the higher the coefficient will affect the tone, but it will help the bass performance.

8Conversion speed: the ability of the highest amplifier stage of the power amplifier to amplify the strong signal excitation mechanism into high-voltage, high-current AC audio in a unit time. High-end models above 30V/US, individual over 50, high ratio, good conversion ability, music level and dynamics, when combined with speakers, it can be more reproduced according to the original sound, a good power amplifier can improve the sound imaging power , Analytical power and strength.

Source: NetEase Auto