Basic knowledge of automobile maintenance (17)

car repairBasic knowledge (17)

-Car stereoInstallation technology

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6. Installation
1.First understand the original car system
For the size of the original car's mainframe space, understand its mainframe functions (if there is a CD, etc.), the installation position and size of the front horn, the installation position and size of the rear horn, and whether there is an original car amplifier.
2.Learn about the newly installed audio system
3. Wire selection, attached (power cord calculation table)
Minimum recommended size number (Gauge)

Total current demand of the whole system Length 0-4 feet Length 4-7 feet Length 7-10 feet Length 10-13 feet Length 13-16 feet Length 16-19 feet Length 19-22 feet Length 22-28 feet
0-20 amps 14 12 12 10 10 8 8 8
20-35 Amp 12 10 8 8 6 6 6 4
35-50 Amp 10 8 8 6 6 4 4 4
50-65 Amp 8 8 6 4 4 4 4 2
65-85 amps 6 6 4 4 2 2 2 0
85-10 amps 6 6 4 2 2 2 2 0
105-125 amp 4 4 4 2 2 0 0 0
125-150 Ampere 2 2 2 2 0 0 0 0

This calculation table is suitable for the condition that there is copper wire and the voltage drop is not less than 0.5 volts. If aluminum or tin materials are used, the size of the wire should be increased appropriately. The calculation table for the size of the power cord has taken the impedance factor of the contact into consideration. The more efficient expander (not less than 75%) can be reduced by one (I gauge) according to the wire size corresponding to the same wire on the table. However, when using a smaller size wire, the contestant must provide a reasonable proof to show that the efficiency of the power amplifier is not less than 75%.
4.Matters needing attention when disassembling
5.Precautions when installing the host
The installation is stable and adequate support is provided. The surrounding panels or components must be tightly connected to the audio generator, and no gaps or noises should be left.
6.Precautions when installing the power amplifier
The power amplifier and its bracket must be firmly installed without the possibility of loosening, and proper space must be provided with air flow. When installing a power amplifier, the fixed frame of the power amplifier should be properly integrated with the shape and appearance of the space.
7.Precautions when connecting the power amplifier
Connect the ground wire first, and then the power wire. When the signal line is too long, it should not be looped, but must be connected, because it is easy to produce signal amplification interference (including the electronic crossover part).
8.Precautions when installing the speaker
The loudspeaker must be installed so as not to be damaged by external forces. The loudspeaker should be installed on a hard surface or a well-made loudspeaker box.
9.Check the line before power-on
After you complete the wiring, please check the power cord again, and use a multimeter to measure whether the positive and negative are short-circuited before powering on. Check the circuit. If there is no abnormal sound, touch the power amplifier with your hand for abnormal temperature after 10 minutes of warming up.
10.Amplifier crossover settings

Seven. Subwoofer
1. What is subwoofer?
The sound with a vibration frequency below 90 Hz is called subwoofer, because it has a long wavelength, so it has no directivity. Taking 70HZ as an example, the wavelength is approximately equal to 4 meters, because the frequency and amplitude are relatively large.
2. Why do you need a subwoofer?
Generally, the speakers on cars are usually five inches or six and a half inches, and its low frequency response is limited. For lower frequencies, it can only be done by a larger subwoofer, because lower frequencies require greater stroke; A five-inch or six-and-a-half inch speaker has a short stroke and it is difficult to obtain a lower frequency response, so adding a subwoofer can increase the width of the sound field, just like an orchestra without a bass guitar or cello, the sound will become monotonous And nothing fills the entire space.

3. What equipment do I need to install a subwoofer?
The size of the subwoofer can generally be divided into: 8 inch, 10 inch, 15 inch, 18 inch, etc. In addition to the speaker, you also need a power amplifier and electronic crossover. The power amplifier is used to drive the speaker and divide the sound. The function of the device is to divide the frequency and confirm the range. The sound above the ultra-low frequency is filtered out, and only the ultra-low frequency signal enters the power amplifier to drive the speaker.

a.Subwoofer form
In addition to the infinite baffle-type subwoofer, all need to be installed in the speaker. The form of the speaker is different according to the characteristics. Generally can be divided into the following types:

1). Closed type
This is the easiest speaker to make with the smallest volume and large power, and the failure rate is very low.
2). Reflective (breathable)
This type of speaker has a larger volume, a lower frequency response, and a higher volume.
3). Band type
The sound output of this kind of speaker only has a certain frequency band and the lower or higher frequency is cut off.
4).Push-pull
The efficiency of this kind of speaker is very high, the phase of the two speakers is opposite, and the volume is not large.
5). Free space
This kind of speaker does not need to be made, but a free-space speaker is directly hung on the top of the tail box.

b.Matters needing attention when installing a subwoofer
The power amplifier that drives the subwoofer consumes a lot of current, so the wire diameter (core) of the power cord must be enlarged. If it is installed on a four-door car, the ventilation of the rear baffle affects the power of the horn, and the correct phase of the horn will affect the overall performance.

4.Subwoofer design

Volume calculation method of speaker

1. Square and rectangle W×H×D=A

2. Trapezoid (E+D)÷2×W×H=A

Balanced signal transmitter
An advanced audio system has two most important basic conditions, that is, a wide dynamic range and low noise.carThe wide dynamic range in the audio must have very low noise, including the acoustic environment and electrical noise must be very low. In the past few years, in order to achieve this target, assemblers began to reduce engine noise and use sound-absorbing materials, but cars always have a lot of noise. Fortunately, new technology will change all of this.
All the assemblers know that the signal line must be far away from the power line, but they have no choice in the telephone connection of the telecommunications bureau. They have to walk side by side along the high-voltage line for hundreds of kilometers. You hear 60HZ AC noise on the phone. NS? The telecommunications company was the first to develop balanced signal lines, which would not cause noise even if they were transmitted for several kilometers.

What is a balanced line?
In an unbalanced car audio system, the signal connection of each channel is composed of two wires. (From the main unit to the amplifier) ​​The center of the general coaxial cable is commonly called the live wire, the separated part is called the ground wire, and the ground wire part is connected to the iron shell of the car.Accessories: Like a lamp,Dynamo, The electronic circuits are all returned to the negative terminal of the battery through the iron case. At this time, the induced noise will be amplified together, because the unbalanced amplifier cannot distinguish between the signal and the noise balanced line, and it has its own ground. The loop, the amplifier part is like a differential amplifier, one input signal is opposite, the other is reverse phase, and the noise is the same phase, so it cannot pass. Simply put, balanced transmitters and receivers can eliminate noise and increase dynamic range.
Basically it is composed of three components:

1. launcher.
2. Balanced signal line.
3. receiver.

The most advanced amplifier is to put the receiver inside, if it is an old amplifier, the above three components are required.

8. Getting started with car audio tuning
An expensive car audio system, even if you install advanced equipment, if not tuned or improperly tuned, the entire audio system may be worse than the original car audio.
The basis for the success or failure of tuning is based on the quality of construction. Incorrect installation methods and wiring methods will make tuning more difficult. In fact, more than half of the tuning content is correcting errors. These errors come from system design, equipment matching, installation methods and wiring methods. If these errors are not corrected, the tuning work cannot be carried out.
Everyone who works in car audio has experience in tuning, but most of them are still groping and gaining experience from failure. In fact, even if you feel that you have completed the work, you may feel that you are not satisfied. Because it can be better.
Many people may encounter various problems in the process of adjusting the sound system. If these problems are not solved, the sound system will hardly perform well.

Functions of basic equipment:
1. Host: Control the soul center of the audio system, and provide the audio source to the audio system. A good audio source can make the system sound better.
2. Pre-amplifier: The signal that has not been amplified and amplified is called the pre-stage signal. Generally, the signal conveyed by the RCA signal line is the pre-stage signal. Some mainframes have a small output signal, which is unfavorable for the rear loudspeaker drive and can easily cause noise interference. Therefore, a pre-amplifier is required to amplify the mainframe output signal from 0.5V to 3V or 7V.
3. Amplifier: Amplify the front-level signal to drive the speaker. According to the circuit structure, it can be basically divided into A, B, AB, D, etc. The output power marked by the general product is the instantaneous power, and the power marked by the more advanced product is the actual effective power.
4. Electronic crossover: Its basic function is to divide the frequency, according to the amplifier connected to the speaker for different frequency range allocation, generally can be divided into two-channel, three-channel and multi-channel hybrid, some with multiple functions Or merge it on the amplifier.
5. Equalizer: trim the uneven frequency response, because the car environment is different, the response obtained by the horn sound is also different, so it needs to be trimmed, generally can be divided into 5 bands, 7 bands, 15 bands, 30 bands and parametric type Equalizer.
6.StabilizationcapacitanceDevice: store electric energy, fast discharge, supply system needs, filter power clutter, reduce distortion rate. According to the capacity, it can be divided into 500,000 microfarads, 1 million microfarads and 2 million microfarads.
7. Horn: A device connected to the amplifier to make a sound, vibrating in accordance with the AC signal output by the amplifier to make a sound.
8. Wire: Many different wires are required to connect these audio equipment, which can be generally divided into power wires, signal wires, and speaker wires. The wire diameter of the power wires affects the performance of the amplifier, while the quality of the signal wires affects the frequency response of the system. , The thickness of the speaker wire and the quality of the copper wire also affect the sound performance.

The basic steps of tuning:
After you complete the wiring, please check the power wiring again, and use a three-meter to measure whether the positive and negative poles are short-circuited, and then turn on the power after making sure that it is correct;
Turn the volume to the minimum, then turn on the main unit. If you hear any abnormal sound, please shut it down immediately. Check the circuit. If there is no abnormal sound, touch the amplifier to see if there is any abnormal temperature after warming up for ten minutes.
1. Tuning method of host + coaxial speaker:
Turn up the volume, test whether there is prematurely distorted sound, balance the left and right at high speed, check whether there is a 180 ° phase difference, find a cassette or CD with monotonous vocals and musical instruments, and place the LOUND OFF BASS button and TREMBLE button on the main unit in the middle. Then test whether each speaker has the same performance to the human voice. If there is a spectrum tester, test the ratio of high and low sounds. If not, listen to it by ears.
Turn the volume down to a very low level. If there is a sonorous treble, it is very obvious, it means that the high volume is too much. In addition, strengthen the BASS button to listen to whether the bass fixation is intact, whether there is abnormal sound, and whether the low frequency performance is very good. If the low frequency is insufficient, you can increase the BASS button. If the brightness is not enough or the treble is too much, you can adjust the TREMBLE button. Finally, adjust the FADER to feel the positioning. Change the music in this way and repeat the above steps several times.
2. Tuning method of host + coaxial speaker
Basically the same as the method in 1, if the treble volume is too much, you can reduce the treble volume for balance.The method is as follows: connect 5W cement in series and parallel between the crossover and the tweeterresistance.
The + end of the treble should be placed in the normal position. If the crossover has -3dB and 0dB, it should be placed at the 0dB position. Because the -3dB position has a resistance inside the crossover, the impedance will change for the amplifier.
3. Host + amplifier + speaker
First set the sensitivity of the amplifier, turn it off to the minimum, then turn on the volume of the main unit to 80%, then increase the sensitivity of the amplifier until the speaker has a distorted sound, and then reduce it a bit, this point can get the best signal The noise ratio is the same as that of combination 1.
4. Host + electronic crossover + amplifier + speaker + subwoofer
First put all the volume controls on the main unit in the center, then turn on the volume to 80%, and turn off the sensitivity of the amplifier to the minimum. Now turn on the input gain of the electronic crossover and place it in the middle, and turn on the input gain of the amplifier for approx. Then increase the output sensitivity of the electronic crossover until the speaker has a distorted sound, and then reduce it back to this point. All the sensitivity has been set, and then start tuning. First, turn off the middle and high tones of the front and rear channels. Listen to the subwoofer, adjust the crossover, so that the subwoofer can work naturally, and there is no mechanical noise or other resonance, and then add the mid-range and high-range, adjust the ratio of mid-range and sub-bass, lower the volume of the rear channel, and then Then test the phase of the subwoofer, and change the phase of the subwoofer by 180° at low volume, that is, positive and negative reverse pull or 0°～180° on the electronic crossover.switch, See which phase volume is the correct phase. After all phases and frequency ranges are set, make detailed adjustments. Generally, the crossover point of the subwoofer is set between 80HZ～100HZ, and the high pass part The crossover frequency of the mid-tweeter speaker is about 60HZ～90HZ.

How to adjust the equalizer:
When should the equalizer (EQ) be used? When the horn is installed in the car, the frequency response is uneven due to environmental factors, such as interior decoration, structure, and window glass. To trim a single frequency, you need to equalize Device.
The equalizer was first developed by the recording studio. Because you need a flat frequency response when recording. It was later developed into home audio and then applied to car audio. The main function of the equalizer is to adjust the frequency unevenness caused by the sound environment, speakers, equipment, etc. If the frequency of a section is too large or too small, its job is to reduce the too large to make up for the too small. Let's give an example of a single room. When you are playing the piano, if a key is too loud or weak, do you want to adjust it well? If you don't tune, is the sound weird?
What is the circular equalizer and the parameters wait for the equalizer? The fixed frequency and fixed Q value cannot be changed, not a circular equalizer. After the parameter waits for the carburetor, the frequency point and Q value can be changed. Generally, there are relatively few bands. In order to adapt to different curves, it must be changeable.
Equalizers generally indicate a range of +/-12dB. This means that this frequency can be increased by 12dB. The Q value indicates its bandwidth, and the larger the Q value, the narrower the bandwidth.

Many people reject EQ very much, claiming that the signal gets worse as soon as it goes through EQ. That's right! There will be some changes, but often it will not be adjusted and the sound will wait very badly. Below we will introduce the basic method of adjustment.

First put the volume switch of the main unit in the middle, and then set the crossover point, phase, and ratio in the system correctly before adjusting the EQ. Remember! EQ is only for detailed adjustments. There are three basic rules that must be followed:
1. EQ adjustment must not be +/3dB. If it exceeds 6dB, it means that there is a problem with the speaker phase or the frequency in this area.
2. Adjust one frequency or two at a time, and then look at the changes on the spectrum.
3. Please remember that when you increase 6dB, the power doubles and it is easy to make the system prematurely distorted.
After remembering the above three rules, set the EQ control to the midpoint, and then use the spectrum to observe first which frequency bands have a drop. If the drop is greater than 6dB, please check the system or adjust the ratio first. Make sure that the drop is within 3dB. If you have to abandon the drop of some frequency bands because the speaker position cannot be overcome, you can't use EQ to forcibly fill it up, otherwise it will be easy to prematurely distort. Find a CD with a relatively wide range and listen to it first, and then start with the high-frequency part and trim it down. Adjust each EQ control to the maximum and minimum, listen to its changes, and understand the sound range of each EQ control by the way, so that you can fix it. As for what kind of curve is the most ideal when using the instrument? That is to maintain the level from 150Hz to 10KHz, increase by 10dB below 150Hz, and decrease by 3dB above 10KHz.
As for how to adjust by listening? If you don’t have an instrument reference and rely on your ears, you must have good hearing. If you don’t have one, don’t worry. Here’s a trick. As long as you do these actions, you can easily get sixty points. Regardless of whether you are using a passive crossover or an active crossover, the problem is often the frequency near the crossover point, so as long as the EQ control of these frequency points is attenuated by 2-3dB, other In the fine-tuning part, look for ten CDs with different styles of music and different recording levels to listen to and trim them in turn, until each CD can be listened to. Once you have common points, you will be close to completion. It is recommended that you practice more listening skills, which can get twice the result with half the effort.

Nine. How to buy a good power amplifier

The market is flooded with all kinds of imported power amplifiers. Have you been deceived by flashy advertisements?

The following provides some basic specifications of power amplifiers.
1.Exquisite historical cause
The power amplifier is like human beings. Whether its blood is good and pure is related to its evolution or elimination. A good power amplifier must have a high-end (Hi-end) engineer to design a good product and not be eliminated by the market. A good (Hi-end) engineer not only understands the electrical aspects, but also requires the quality of electronic materials plus market demand, so that he can be called a Hi-end engineer.
2.. The power supply of the power amplifier (power supply)
The power supply is the heart of the power amplifier. A strong and powerful power supply is the most basic requirement, that is, the DC voltage (13.8V) is converted into AC voltage and then the working voltage of the power amplifier. In a series of transformations, efficiency becomes very important. Therefore, some power amplifiers in the market emphasize (switching class A) as the truth, and the inductance of the coupling transformer is the most important part.
Generally, the design of power amplifier power supply can be divided into regulated power supply, most power amplifiers use this circuit, and unregulated power supply. What are the advantages and disadvantages of the two? What's the difference?
A stable power supply with a reliable design, it has the ability to deliver a fixed voltage and large current for the power amplifier to work. Assuming that the battery voltage does not maintain the due voltage drop (13.8V), it will not cause the power amplifier efficiency to be insufficient. This is The only advantage of a stable power supply.
If the power amplifier does not need a large current to work, the power amplifier designed with a stable power supply must tightly grasp the large current to maintain the basic operation requirements of the power amplifier, and other electronic systems in the car relatively produce insufficient power supply, resulting in complex power problems. , Once again, it is a stable power supply, there is no way to instantly provide the music dynamic ("dynamic" "punchy") suddenly large, but there is no more current to the power amplifier and cause premature distortion.
The explanation is more thorough, that is, the stable power supply only provides a certain amount of current to the power amplifier, no more, and so much when not needed. This is a stable power supply.
The design of the unstable power supply is improved in response to the shortcomings of the stable power supply.
The advantages are as follows

1 Increase the dynamic range and power of the power amplifier
2 Increase power amplifier efficiency and reduce current consumption
3 Accurately meet the current required by the music signal
4 Reduce the impact on automotive electronic circuits
5 Reduce the money needed to improve the power supply of the car

3. Damping Factor of Power Amplifier
Most power amplifier design engineers believe that the damping effect has a considerable impact on the driving force of the speaker and also affects the sound quality.
What is the damping effect? A simple explanation, similar to the shock absorber on a car, which means that the amplifier pushes the horn to control the amplitude of the cone, so that the horn will not be distorted.
Damping effect in the specifications of the power amplifier, the coefficient should be larger, the better, usually imported power amplifier (200W) 150@4ohm2ohm@75, this is a very important concept, the speakers are connected in parallel, the power of the power amplifier will increase, and the damping The effect will be halved, so users should think twice about this.
The sound performance of the power amplifier with little damping effect will make the bass loose and shapeless, that is to say, the low frequency is dragged, loose, and weak.
The power amplifier with high damping effect has its details and end rhyme in the low frequency performance of music, which is often referred to as Q degree.
4.Slew Rate (Slew Rate) speed sense
Many people have been engaged in the car audio business for decades, but they claim to be professionals but never understand what the climb rate is
Damping effect + climb rate are the two most important coefficients in the power amplifier specifications. It is related to whether the sound of the power amplifier is clean and clear, or is dim and beautiful. Now it should be clear why the power amplifier has clear and fuzzy sound. In addition to appreciating with ears, you can also check from the power amplifier specifications. Found in.
What is the explanation for the rate of climb? It can be compared to how much horsepower and speed the vehicle can reach the end without being overtaken by the latter. In terms of sound explanation, when listening to a beautiful piece of music, the volume can be slightly louder. If you hear a harsh sound like a nail scratching a blackboard, it means that the speed (climb rate) of the power amplifier is not fast enough to accurately perform high. The delicate and relatively high-climbing power amplifier of the frequency part should express the sense of sound field in music, the sense of delicateness and the pine fragrance that can be expressed by stringed instruments.
5. The basic specifications of a ZAPCO power amplifier are as follows:

Power per channel-stereo (power amplifier stereo power) THD+N@1KHz (total harmonic distortion)
50Watts×2 @ 4Ω <0.02%
Power-Mono (non-stereo output)
100W×1 @ 8Ω <0.017%
Frequency Response (Frequency Range) 20Hz~20KHz+ 0dB-0.35dB
S/N ratio (signal-to-noise ratio) >100dB (the bigger the better)
Transient Distortion (transient distortion) <0.01% (the smaller the better)
Separation (Separation) >60dB
Damping facor (damping effect) >900 @ 4Ω@ KHz
Input Sensitivity (input sensitivity) 1~4volts (voltage) and 4~16volts (voltage)
Slew Rate (Climb Rate) 26v/uS
Idie Current 1.75amperes
Dimensions (diameter) 2.375”H×8.75”W×13.5”L