The sound reinforcement project is a means of processing the original sound by means of acoustic and electroacoustic means, so that the listening effect achieves the desired effect.
The sound reinforcement system is divided into an indoor sound reinforcement system and an outdoor sound reinforcement system. The difference between the two is very large during operation. The indoor sound reinforcement is greatly affected by the room acoustic conditions, and the outdoor sound reinforcement is more affected by the natural environment. The design of the sound reinforcement system is very targeted, and the selection and use of the equipment are different due to different applications. According to the purpose, the sound reinforcement system can be divided into: language sound reinforcement system, music sound reinforcement system, stage sound reinforcement system and so on. Although the sound reinforcement system differs according to the equipment and peripheral equipment selected, the brand, function and quality will be different, but the core is consistent, that is, under the premise of achieving the purpose of sound reinforcement, the quality of the sound is guaranteed. Figure 1 shows a relatively complete sound reinforcement system.
1. The problem that the microphone is easy to occur in the sound reinforcement work The microphone is the first link of the sound reinforcement system, and its quality and performance are crucial to the sound reinforcement system. Depending on the requirements, you can choose a wired microphone or a wireless microphone. Wired microphones have a wide frequency response range, high sensitivity, low distortion, good transient effects, but poor mobility. Therefore, they are used in fixed places. Wireless microphones are more widely used due to their aesthetics and flexibility, but they are needed in use. Avoid problems such as blind spots. Pay attention to the following issues when using the microphone.
1.1 Wired Microphone 1 Impedance Matching The conversion of the acoustic signal to the electrical signal is based on the premise of ensuring high fidelity of the audio signal. To achieve this, the load of the microphone must be greater than 5 times its internal resistance (microphone output impedance 5Zout = mixer input) Impedance Zin), such a mixer input impedance is used in conjunction with the microphone to not affect the normal operation of the device. Although the output impedance of the microphone and the input circuit of the mixer will have some energy loss in use, it can be compensated by the amplifier's amplifier circuit, otherwise it will not only affect the output level of the microphone, but even cause signal distortion. The transmission power is maximized only when the impedance is matched.
2) Phase problem If you are connecting multiple microphones on the mixer, you must consider the phase problem. When the phases of the two microphones are opposite, the signals will cancel each other when they are sent to the mixer. The phenomenon is that the sound is significantly smaller. The solution is to adjust the wiring of one of the microphones and re-weld. Each microphone's jack can only be connected to one microphone. Never use it in parallel, because it will change the state of the microphone load, causing many unexpected troubles. When working with more than two microphones, the distance between the two microphones is equal to the distance from the source to the microphone, since each sound source directly reaches the signal strength of the microphone closest to it and the signal strength of the signal reaching the adjacent microphone is substantially equal. More than double, the interference phenomenon is relatively weak, the industry calls it the "Three One Principle."
1.2 Wireless microphone The wireless microphone can convert the picked up audio signal into electromagnetic wave and transmit it to the audio signal after receiving it by the receiver. It is convenient to use without the microphone line. This kind of microphone is suitable for working in close range. The disadvantage is poor anti-interference ability. In the work, sometimes there will be signal loss, that is, "dead point". The phenomenon is that the pickup signal is extremely weak or even disappears, which will seriously affect the work.
1) The wireless microphone system consists of a microphone head, a transmitter and a receiver. There must be no object blocking between the transmitter and the receiver to prevent the receiver from receiving the signal.
2) If there is a camera service on site, the antennas are set higher than the camera and lower than the light frame. This is because they interfere with the working frequency of the wireless microphone to cause a blind spot of the electric wave or disorder the propagation path of the electric wave.
3) The RF signal indicator on the receiver is the most intuitive display of the receiving state of the signal, so it must be placed within the scope of the sound engineer's observation to take timely action according to the display status.
4) The wireless cartridge is selected by the knob. After the selection, the knob should be fixed to prevent misoperation.
2. Noise and feedback phenomenon elimination methods 2.1 Noise phenomena and elimination methods There are many reasons for the noise generated by the sound reinforcement system. In summary, it can be determined in three aspects: the noise generated by the power supply equipment, the noise generated by the external electrical equipment, and the same as the system itself. There is noise.
1) Noise generated by power supply equipment This phenomenon rarely occurs in high-standard sound reinforcement places, because these places have considered the power supply interference noise problem before construction and solved it in the Ding design. This phenomenon occurs mostly in places where the sound reinforcement conditions are not very good. For example, in some places, the change of the stage lighting is not realized by changing the voltage, but the electronic circuit is used to control the conduction rate of the thyristor, and the method of controlling the waveform area of ​​the alternating current is used. Control the output power to change the light and shade. This method causes noise in the sound reinforcement. For this phenomenon, two of the three-phase power can be used for illumination, and the remaining phase is supplied to the sound reinforcement system. There is another possibility for the occurrence of noise from power supply equipment, that is, interference from power grid noise. The Zhoujia grid is public, and household electricity and plant equipment are running in parallel on the grid. These devices will cause voltage drops and unpredictable noise sources due to excessive power consumption. For these noise sources, measures can be taken in their own work to eliminate noise. If you can use a voltage regulator to increase the low voltage, adjust it to about 220 V, the electromagnetic circuit inside the regulator can also eliminate some noise waves in the power supply. After the voltage regulation, the regulated voltage can be used to make the adjusted voltage relatively stable. The voltage regulator can identify the voltage value higher or lower than 220 V and correct it to the normal range through the servo circuit.
2) Noise generated by external electric waves This kind of interference is mainly for wireless microphones. Now there are many wireless communication devices, and even taxi scheduling has wireless calling systems. Therefore, it is best to check whether the microphone transmits and receives frequencies before using wireless microphones. Can be adjusted to avoid those frequencies that do not want to smash, choose a wireless microphone that can work in the UHF (Ultra High Frequency) band, the chance of problems will be smaller. The grounding point of the sound system must be independent (not shared with the power supply). If the system input is grounded, the output is also grounded.
The noise signal has been amplified, is not easy to eliminate, and it is easy to generate feedback because the input and output terminals are equipotential.
3) The inherent noise of the system In Figure 1, you can see the peripherals of various audio processing. However, these devices are double-edged swords: on the one hand, it helps the sound engineer to complete the sound reinforcement task, on the one hand, because of the connection of multi-level equipment. The generated electrical noise affects the quality of the sound reinforcement work. If such problems occur at work, the sound engineer will judge which level of system noise comes from and try to solve it.
After turning on the power, if there is noise, first cut off the power of the wireless microphone receiver. If there is still noise, it indicates that the crux is not at this level; you can turn off the CAIN knob in each channel on the mixer, if there is noise on a certain road. No, the problem is here. If all the input channels are off and there is noise, proceed to the next step; turn off the power of the mixer, so that the entire mixer includes bus, group, return, auxiliary, and total control. Intercoms, intercom and oscillation systems are checked; if there is noise, check peripheral equipment, such as exciters, compressors, feedback suppressors, equalizers, dividers, effects, and amplifiers. This work is very tedious, and it is necessary to judge one by one, and then determine which device the noise comes from before processing.
When playing an electronic musical instrument such as rock music, after the actor's own electronic musical instruments and electro-acoustic equipment are used repeatedly, some connectors are loose, which may cause noise due to poor contact. This kind of noise is sometimes absent, the volume is loud during the performance, the noise is blocked, and the noise is very prominent when the performance stops. The experienced musician will turn off the power of the instrument immediately after the performance stops. Ping off), so that the noise of the instrument can not enter the sound reinforcement system, but the inexperienced musician does not have such a good habit, which requires the sound engineer to immediately put the corresponding fader at the end of the electronic instrument performance. Pull down to remove the noise to prevent the occurrence of noise problems.
2.2 Feedback phenomenon and elimination method The howling of the sound reinforcement system is very unpleasant. This is the acoustic feedback. Acoustic feedback is the positive feedback generated after the signal is superimposed and amplified multiple times. This phenomenon affects the normal operation of the sound reinforcement, and burns the equipment when it is large. Therefore, the elimination of the feedback phenomenon is an indispensable skill of the sound engineer. According to the author's experience, there are at least three reasons for the feedback phenomenon: the first is that the gain is too large, the second is that the microphone is in the sound release area of ​​the speaker and is close to the speaker position, and the third is improper use of the device.
Some sound engineers drive the mouth on the input channel of the mixer very large, and the fader only pushes up a little. This is wrong because in the actual work, once the scene has a climax, the volume is too loud, the sound engineer will definitely Instinctively pull the fader, and the fader has no margins down, which will make the work very passive, and can not rule out that after the long-term work of the mixer, the lower part of the fader wear must be more serious than the upper part. There may be noise. The correct way to do this is to first turn off the gain, push the fader to 4/5 of the full stroke, and then turn the gain knob to the appropriate position. In the sound reinforcement station of the radio station, it is often seen that several or even a dozen faders are basically on the same straight line, and the mouths are different. Some sound engineers also use white adhesive tape to stick on the top of the fader. A straight line is used as a mark. This white line is close to the "howling" point. These are all tested in the preparation work and are very practical. The working environment can't be changed greatly because of the need of sound reinforcement. Therefore, the sound engineer should learn to avoid the problem when the conditions permit, for example, the distance and angle of the microphone and the speaker are often neglected, and the speaker produces If the sound enters the microphone, it will produce feedback. If the microphone is too close to the speaker, and the speaker is facing the microphone, it will bury the hidden danger. Therefore, be sure to pay attention to the distance and angle of the speaker when placing the microphone. Feedback can also be eliminated with the device, and the acoustic feedback suppressor, frequency converter and equalizer all have the effect of eliminating feedback. Any problems may occur in the sound reinforcement work, so it is necessary to prepare in advance, select equipment according to the specific work conditions, and carefully check the equipment after selecting the equipment. The knobs and buttons of the equipment should be correct. Use a wireless microphone, be sure to remind him not to play near the speaker, so as to avoid feedback.
3, the preparation of different sound reinforcement tasks should be done well, the business ability and responsibility are indispensable. The radio's sound reinforcement tasks are of different nature, with a wide variety of political conferences and public performances. Therefore, the sound engineer should carefully prepare all the parts of the sound reinforcement according to the different tasks, and strive to complete the task satisfactorily.
3.1 Political sound reinforcement work The sound conditions of this sound reinforcement work are generally better, so the technical work is relatively less, mainly because the sound pressure of the sound engineer is great, and the preparation for perfection is the best decompression. Measures.
The author's experience is to fully understand the situation at the work site under the conditions that he can control. The equipment must be reliable. It is best to use the equipment that you are familiar with. After the installation and debugging, put some useful data on the book and collect it. Make sure that the connection and the latch board are in good contact. After the equipment is adjusted, it is best not to stay away from the scene. Keep in touch with the guards to ensure that the unrelated personnel do not approach the sound reinforcement equipment.
There must be no feedback whistling during the conference or performance. The sound engineer should find out the whistle when the joint adjustment is made (intuitively reflected to the position of the fader). It is best to mark the scale on this console. And keep a safe distance from work.
The best sound-amplifying effect area should be based on the position of the head. The effect of listening here should be guaranteed to be the best. Before the performance, the sound engineer should listen to these seats. If possible, please ask the industry staff (such as the director) for common staff. .
If it is a high-performance performance, the scene will be very large, and there will be more microphones, but you can't always drive all the microphones for a long time because you are afraid of missing the signal. This will not only cause too much noise, but also cause Feedback. This requires the sound engineer to be highly concentrated in the tuning process, and there must be no accidents of the microphone mute (forgot to push a fader), so it is best to carefully understand the performance type of each program, and in the program list. The detailed operating procedures for each program are marked to avoid operational errors.
3.2 Public interest performance sound reinforcement work This kind of activity is mostly held in the open air, although there is no indoor acoustic problem, but the sound energy loss is very large, so the outdoor sound reinforcement audio equipment must have enough powerful power rating, facing the open space The live audio equipment should also have sufficient penetration, otherwise there will be problems listening to seats that are farther away. The sound engineer should make plans for the configuration of the equipment in advance. Regarding the installation and commissioning and some special requirements, it is necessary to negotiate with the relevant departments in advance.
The venue for outdoor sound reinforcement work is generally chaotic. Be sure to do the protection measures for the audio system line. Cover the line with the cover according to the actual situation. Stick the wire harness to the floor with the rubber strip to avoid being kicked.
Understand how the backup power supply will be provided in an emergency, and ensure contact with the person in charge of the on-site power supply. In the event of a power outage, immediately use the correct treatment to minimize the loss. There are many unpredictable situations hidden in the outdoor sound reinforcement work. If there is a problem, it must be calm, and it is the most important thing.
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