Open-air sound system design and tuning

Selection and system design of outdoor audio system The design of audio system involves a wide range of factors. According to the characteristics of outdoor audio, which is used in different places and environments each time, it is advisable to choose to use temporary installation mobile type. Follow the principles of practicality and applicability, so that the purchased equipment is not idle, fully exerts its functions and is easy to operate, etc. At the same time, the consistency of the performance of the equipment files should be maintained to avoid the phenomenon of "mismatch". As an outdoor audio system, the selection should also consider the stability and durability of working in harsh environments.
Like other audio system designs, outdoor audio should master the configuration ratio when establishing the power configuration of speakers and amplifiers. If the power "margin" of the power amplifier is insufficient, it cannot cope with sudden instantaneous peaks, resulting in high volume and rough sound quality. If the instantaneous peak volume is 10dB of the normal volume, a 100W amplifier is required to play back the sound with an average power of 10W. When the mixer fader is too large or the microphone sound feedback causes self-excited howling, it is also easy to damage the speaker. For small outdoor audio systems, a strong power reserve is required. Generally, if the outdoor sound field increases the sound pressure level by 3dB, the power needs to be increased by 10 times. The specific value of the sound field can be calculated according to the sound pressure level = 20log (P/P0). When the continuous undistorted power of the power amplifier is 1.2 to 1.5 times the rated power of the speaker, the equipment can be guaranteed to work safely and stably.
The preliminary preparations for open-air sound are different from other fixed sound systems. The preliminary preparations for open-air sound are particularly important, including familiarity with the venue, power supply guarantee, cable laying, etc. If conditions permit, you should be familiar with the geographical location of the venue one day in advance and establish the layout points of the sound system. On the day of the event, make preparations in advance to ensure that everything is foolproof.
The energy of the sound system comes from the power grid circuit. If the power circuit fails, the system will not make any sound at the least, and the sound equipment will be destroyed at the worst. Therefore, the power circuit should be guaranteed to work normally. For remote areas, if conditions do not permit and temporary generators are used, they should be protected by specialized personnel. Before adjustment, use a multimeter to measure the voltage of all power sockets to confirm that the equipment is well grounded and the power wiring phase is consistent. Poor grounding or phase error often causes interference and noise intrusion, resulting in deterioration of the sound effect.
The laying of various cables must be accurate and in place according to the layout position. When laying out the cables, they should be done carefully and marked as clearly as possible as a basis for searching during installation and maintenance. Do not mess up the cables. At the same time, sufficient margins should be left for each cable, and the connectors and plugs of each equipment should be connected correctly. When laying out the cables, carefully check whether each cable is damaged or of poor quality. If there is any, replace them all immediately. For the laid cables, especially the speaker lines, special personnel should be assigned to protect them to avoid failures caused by disconnection and short circuit of the speaker lines due to frequent activities of the venue personnel, and even damage to the power amplifier. Outdoor sound adjustment and precautions Outdoors, the sound pressure will decay with increasing distance. To overcome this problem, the speaker placement position must be raised, and the speaker can be hoisted if conditions permit. Shorten the distance between the front and the back. At the same time, it can also overcome the problem that the sound waves of the low-position speakers are absorbed by the front row audience, resulting in large losses in the mid-high audio frequency, which affects the audience in the back row. For the speaker type, it is recommended to use outdoor dedicated speakers or mid-high horn speakers.
After confirming that the speaker position, power supply, and cable connections are correct, you can turn on the mixer in the order of sound source (CD, VCD, MD, VCR), mixer, and amplifier (the order is reversed when shutting down), and then debug the mixer.
(1) Adjust the amplifier volume control potentiometer to the maximum position; set the mixer accompaniment music and microphone branch faders to 0dB; the GAIN input gain of each branch is in the adjusted position; the mixer total fader is at the minimum position; the mixer sound quality compensation knob is in the middle position;
(2) Debug the accompaniment channel, select familiar songs, pay attention to the appropriate volume, and repeatedly adjust the GAIN gain and EQ sound quality compensation until the sound effect is satisfactory.
(3) Debug the microphone channel (the microphone channel on the mixer must be arranged from left to right in a fixed manner according to the venue). For condenser microphones, the mixer should provide +48V power. When adjusting the microphone volume, the branch fader is at 0dB, adjust the GAIN input gain, and the PEAK (peak level indicator) flashes occasionally.
Outdoors, on-site noise and acoustic feedback (howling) must be taken seriously. For the former, you can choose a high-sensitivity microphone. When breathing noise and wind noise are obvious, you should install a windshield and adjust the GAIN knob to ensure that the gain is not reduced. Practice has proved that the sponge windshield will not harm the sound. The high frequency will slip, but it can be corrected by using the mixer EQ. There are many reasons for acoustic feedback, even for high-quality equipment. In practice, as long as some measures are taken, it can still be suppressed.
(1) Keep the microphone away from the speaker and place the microphone away from the radiation area of ​​the speaker as much as possible.
(2) According to the on-site situation, appropriately reduce the volume of the microphone channel. If ringing occurs, lower the volume in time. When the host or other personnel have to pass in front of the speaker, they should also pay attention to controlling the volume.
(3) Compensate for the sound quality through the mixer. When debugging a demonstration performance, increase the volume until the system just produces self-excitation, and then adjust the equalizer knob from the low frequency down one by one to effectively eliminate the frequency point of self-excited howling. According to experience, for the frequency of self-resonance, the frequency can be pulled down by 3 to 5 dB. It is difficult to eliminate acoustic feedback fundamentally. In addition to installing feedback suppressors, compressors, and frequency shifters, you should also master the performance of each device in the system and accumulate experience.