How to avoid noise in the sound expansion system

For the public, when listening to music or watching a good movie, the most feared is the noise of whistling, signal interference, and so on. In the general flow performance, this kind of noise is unavoidable, especially for the mobile stage facilities in the grass-roots culture, and how to avoid it. Noise from all kinds of performances has become a chagrin of the major organizers. Because the flow performance is the saying of "shooting a gun, changing a place", all kinds of cables are temporarily laid, and the performance ends in time, so when the line is laid, the signal line, the sound box line and the power line should be separated as far as possible. When the overlap must be overlapped, a single point cross should be adopted to avoid the power line or the power amplifier. The interference of the electromagnetic field generated by the loudspeaker signal line after the rear to the original signal. When installing speakers, we should also avoid the mechanical noise caused by collisions between components when the speakers are working to resonate around the speakers themselves. If conditions are available, the audio system should be electrically independent of the video and lighting systems, or a power filter is added to the front stage to avoid the noise generated by the pulse interference from the power supply.

And that's the problem of signal and grounding. Land and signal are referred to as reference and subject matter. The signal ground is the reference of the signal. Grounding is usually connected to the earth, but it has nothing to do with the earth in the sound reinforcement system. It is a reference object set in the system, grounding is essential, it looks simple, in fact, very complex, according to its different functions can be divided into functional grounding and protective grounding of two major categories. Functional grounding is also included in the following four categories:

1. Work grounding, also called system grounding, is to ensure the normal operation of the system, to prevent the oscillation of the system and to ensure the reliability of the equipment in the system. It is usually necessary to install a grounding in the proper position to make the device monomer run on the basis of the ground. If the 220V power supply is used normally, the ground wire is the neutral point of the transformer.

2, the logic grounding is to achieve a stable reference potential to set the grounding, also known as the DC midpoint.

3, shielded grounding is to prevent the effect of electromagnetic induction to the system and installed grounding, it is the most complex of all grounding, because it prevents interference from others, but also prevents interference. The higher the interference frequency, the tightness of shielded metal mesh, otherwise it will not achieve the desired result.

4, signal grounding is designed to ensure stable reference potential, which is referred to as the preceding reference.

It is reported that some organizers said that a few years ago in the installation of a government conference hall audio system debugging, the system has been found to have very weak low frequency noise, through repeated inspection of lines and equipment can not be solved. Later, a lot of information was found, and one of the power amplifiers, in contrast to the other two power amplifiers, was switched over, and the weak low frequency noise disappeared. Later, it is believed that the electromagnetic field produced by the loop transformer inside the power amplifier of the reverse phase power is interfered with the electromagnetic field produced by the other two power amplifier transformers. In 2009, before an outdoor large fireworks party, the lighting and sound system was installed, and when the rehearsal was started, it was found that when the light was in the state of light adjustment, the noise was very large. When the light adjustment ratio was 50%, the noise was the greatest, and when the light was dark, there was no noise. In this regard, the author repeatedly analyses the factors such as the laying of the signal line and the power supply voltage. It is found that as the stage lamps are all powered by 2 x 2.5 cables, when the light is in the state of light adjustment, the ripple or self excitation in the power supply causes the sound system to produce the sound, and the author is determined to be the problem of work grounding and signal grounding. Then the power amplifier cabinet is connected to the ground with the dimming silicon cabinet, and the signal line of the sound system is checked at the same time. It is found that the grounding end of a signal line is high, and the system noise will disappear after it is replaced. When the performance is near, the live car of the TV station should pick up the signal from the scene mixer. When the signal line of the live car is inserted into the field mixer, and the noise is very strong, the author immediately realizes that the grounding of the power supply of the vehicle is not equipotential with the work of our site source, and immediately notify the other party to use audio isolation change. The press is isolated from our system. Thus, the sound reinforcement task of the large-scale fireworks show was completed safely. Due to the less application of protective grounding in mobile sound reinforcement, there is not much discussion.

To sum up, the signal and noise are relative and exist at the same time and complement each other. When the signal is different, the noise must be produced, but the noise is not necessarily caused by the difference. In the sound expansion system, the combination of logical grounding and signal grounding and shielding grounding is combined to make the system equipment work in the unified potential. It should be emphasized that the input end of the same device can not be connected with the signal output, and the output of the front stage can only be lost to the rear stage. Connect to the ground, otherwise the signal may float through the feedback of the ground wire. Of course, it is difficult to completely eliminate the noise, only to control or reduce the noise voltage as far as possible, improve the signal to noise ratio of the system, so that the noise is not caused by interference.

In order to ensure the quality and safety of each flow performance, to give people the sound of sound music, we should carefully check the signal cables and try to choose the reliable cables of the shielded welding points. When laying, we should try to isolate the equipment that may interfere with the cable. The same power should be used as far as possible to prevent the electricity from different transformers. Noise is produced by different positions.