Sources and elimination of acoustic noise

After using the car audio or replacing the audio, the audio will produce a variety of noise, the noise can affect the sound quality, reduce the audio index, and even make the entire audio system unable to listen, for noise problems, introduce the source of noise and basic methods of elimination.
1. The source of noise
Noise can invade the car audio system from the following ways.
1. Invade the power cord (enter the system through the host and power amplifier power cord).
2. Current through the ground wire (through the ground wire of the antenna and the ground wire of the power amplifier).
3. Inducted by other wire harnesses (received through the antenna and induced by the original vehicle harness).
4. Interference with electrical appliances (electric horn, motor, etc.).
Items 1, 2, and 3 are relevant.
2. Countermeasures against noise
The parts generally used to deal with noise include automobile capacitors or coaxial automobile capacitors (especially effective in dealing with high-frequency noise), dormant coils (inductance), LC filters, ground wires, diodes, etc.
1. Deal with the noise generated by the ignition system
Check whether the capacitor of the ignition coil positive pole is connected to the ground. For example, check whether the capacity is reduced. If the capacity is reduced, the platinum contacts are easy to ablate and generate interference sparks. You need to replace the non-polarized capacitor with a capacity of 0,5UF / 400V.
Check whether the ignition high-voltage wire uses carbon wire. If the wire type is used, it is easy to cause interference. Because the interference of the radio part is serious, it must be replaced.
The method of increasing the damping resistance can be used to suppress the spark noise. The method is to use a 1 megohm resistor in series with the main high voltage line of the ignition coil output to reduce interference.
2. Elimination of motor noise
First, keep the audio equipment and signal line away from the motor and the motor line. You can use a non-polar capacitor in parallel at both ends of the motor, or you can use two inductors in series with the positive and negative lines of the motor, and then use two non-polar capacitors Connected to the positive and negative lines of the motor, and the other end is grounded to form a filter circuit. The function is to absorb the sparks of the motor carbon brush to reduce noise.
3. For the noise generated by the electric horn without a relay, the following methods are mainly eliminated:
Connect a capacitor to the ground of one of the speakers in parallel with the ground.
Connect an inductance in series with the terminal of one of the speakers, and then connect a capacitor to the ground.
Use the method separately on the terminals of the two speakers.
Connect a capacitor in parallel between the horn button contacts of the steering wheel.
4. For the noise generated by the electric horn with relay, the following methods are mainly eliminated:
The electric horn bracket should be in good contact with the car body.
A capacitor is connected in parallel across the relay contacts, or a capacitor is connected in parallel across the contacts.
® Use the 3, Medium, and ¯ methods.
5. Poor grounding will produce noise.
If the head cover fails to be firmly grounded, the entire head cover will become an antenna, radiating the noise generated by each part of the car to the surrounding space, and introducing the sound system from the antenna and various circuits. When the connection line is added between the front cover and the body, the paint, oil stains and dirt on the contacts must be completely eliminated.
There should be a good connection between the engine (engine) and the body, or between the front wheel suspension and the body, and between the exhaust pipe and the body.
6. Power line noise suppression:
In order to effectively eliminate the noise generated by the power cord, install the ERW * near the power amplifier. If there are multiple power amplifiers, a donut ring should be installed near each power amplifier, because noise can be transmitted from one power amplifier to another, making a single donut ring invalid.
7. Suppression of the incoming noise of the signal line (RCA):
The signal cable should be far away from the power cable and installed on both sides of the vehicle body with the power cable, so as to avoid the possibility of interference. If the signal cable has a double-layer shielding net, the outer shielding net should be connected to the cabinet.
Many problems will be encountered in practical applications, but it is important to find the source of interference first, and then treat it with the right symptoms, so that every program played by the car audio system is clear, pure and perfect.
Noise problems are the most common and difficult to eliminate in car audio faults. Because the structure and wiring of the car are more complicated and there are many places that are prone to noise, so you should master some knowledge of car circuits and car audio, and trouble shooting can be handy. .
Removal method: First, according to the noise situation, through principle analysis and judgment to find out where the fault is, and then take different removal methods.
Simple elimination method, first listen to the sound of the radio, the tape and the CD are all noisy. If there are any, you should check the power cord, ground wire, signal cable, the location of the wiring is reasonable, whether the signal cable is loose or not. , The power amplifier should be insulated from the body. According to different noise sources, different measures are taken to deal with it. If the noise cannot be eliminated, the noise signal source is processed, and then the noise prevention measures are taken, so that the noise can be completely resolved.