The debugging and installation of the live sound reinforcement system is a huge system project, especially in the sound reinforcement system of large-scale performances, the main sound engineer must have rich on-site experience, macro and clear system ideas, extraordinary courage and no change. Stable mood and meticulous and rigorous work habits of each team worker.

　　In the face of such a complicated and huge system project, it is almost impossible to simplify the description. Today, we will only briefly talk about live analog system and sound debugging in live sound reinforcement system. Some of the basic steps in the majority, I hope to help friends who are interested in the field of sound reinforcement.

　　1

　　About debugging

　　1. Line inspection

　　According to the system circuit drawing, carefully check the circuit connection to confirm that the circuit can work normally.

　　2. Setting the initial state of the device

　　Set the power amplifier input to *small, and set the input and output knobs of all peripheral devices to the 0 decibel position or the middle position. Turn on the power in the order from the front stage to the back stage (do not turn on the power amplifier first). After checking that all devices are properly powered, power on the power amplifier.

　　3. Initially check the system status

　　At this time, properly open the gain control of the power amplifier, play a familiar CD, and adjust the mixer input level to the basic normal position. Slowly push up the mixer fader, listen to the sound from the speaker is normal, whether it is distorted, if not normal, immediately shut down and check.

　　4. Speaker and system polarity detection

　　After the system is basically normal, turn on the power of all devices, set the power level to the maximum, pull down the mixer output fader, connect the phase meter generator to the mixer input channel, turn on the phase meter power to adjust the output gain and the mixer The input gain to the mixer indicator table is 0 dB. Slowly push up the mixer output fader and wait for the "pop" sound in the speaker to reach a sufficient loudness (if the loudness is not enough, the test results are sometimes inaccurate), use the phase meter detector to check whether each speaker is in phase or with the speaker The description of the manual is consistent. When testing, it is best to turn off other speakers to prevent interference, and it is more accurate to test one by one. If there is any abnormality, check whether the speaker cable is reversed or whether the system cable is reversed. Adjust it or change it before checking.

　　5. Phase adjustment

　　If the combination of ultra-low frequency and full frequency is used at the same time, due to the existence of the crossover system and the installation location, there may be phase problems caused by cross-frequency interference or different delay times, so phase adjustment is required. The pink noise generator is connected to the input channel of the mixer, and the level is adjusted to the normal position. The phase meter test microphone is placed in the middle of the venue, forming an equilateral triangle with the speaker.

　　Push up the mixer output fader, and check whether the spectrum analyzer screen has a valley point in the frequency band near the crossover frequency of the full-frequency and ultra-low frequency speakers. If so, increase the corresponding frequency band of the equalizer. If it cannot be improved, there is a phase problem. The appearance of the phase problem will directly affect the sound quality, and it is just solved by the equalizer. To solve the phase problem, it is necessary to adjust the phase angle of the crossover or the delay time between the speakers.

　　When adjusting, pay attention to the spectrum analyzer display. First adjust the phase angle of the low-frequency crossover to see if there is any improvement. If there is an improvement, determine the best value before adjusting the delay time. The adjustment of the delay time depends on the scene. If the low-frequency speaker is close to the seat, you need to adjust the delay of the bass, also looking at the spectrum analyzer screen, adjust the delay time to make the curve as flat as possible. Reduce phase interference to the lowest.

　　6. Frequency equalization

　　After making the above adjustments, the next step is to adjust the frequency response curve of the system. Put the test microphone of the spectrum analyzer at a certain position in the seating area, play the pink noise sound source, watch the spectrum analyzer display, and use the equalizer to correct the defective places. Put the test microphone in different places, change several positions, and adjust the balance repeatedly to make the frequency response curve of each area as straight as possible.

　　7. Debug dynamic control equipment

　　Generally, the dynamic adjustment equipment is a compressor. If the compressor is connected in series with a chain, it is generally used as a protection system, so the limiter function of the compressor is mainly used. According to personal needs, only one of the compressor setting methods is described here. The compressor can be set to pass-through (BYPASS), the input and output gain is set to 0 dB, the compression ratio is set to "infinity", and then sent from the mixer The pink noise signal is gradually increased. Observe the input level indicator of the power amplifier. When the clip indicator (CLIP) lights up.

　　Connect to the compressor and adjust the start level knob to turn off the power amplifier input clipping indication. Then increase the output of the mixer by 6 dB or let the output level indicator reach +6 dB, and then adjust the starting level a little bit to make the power amplifier clipping indicator just start flashing. At this point, the level debugging of the system is completed, and the tone adjustment and effect processing (including effects, exciters, etc.) of the sound need to be fully responsible for the tuner. Of course, in audio engineering, this is generally handled by the technicians of the audio company.

　　2

　　Avoid howling and debugging of singing microphone sound

　　1. Monitoring system

　　Adjust the level of a microphone according to the method in step *, without going through the equalization process of the microphone of the mixer, the channel fader of the mixer is placed at 0 decibels (provided that the signal for stage monitoring is taken from the auxiliary output of the fader ).

　　Put the microphone in the main position on the stage, turn on the monitor output master (AUX) and gradually increase the output level. After the microphone causes howling in a certain frequency band, fine-tune the AUX knob to stabilize the howling at a certain volume level, then adjust the equalizer Turn on the corresponding frequency band knob to eliminate the howling in this frequency band, and then continue to increase the level. After the howling in another frequency band is generated, adjust the equalizer to eliminate it, and so on. The flat fader or AUX knob is adjusted to the normal position (such as 0dB), the microphone no longer produces howling, it means that the debugging is completed, restore the mixer fader to the starting position. This method is used to find howling points that easily cause resonance in the sound field, and then appropriately reduce the level of the microphone channel, find someone to speak to the microphone, and then gradually increase the microphone volume to the normal position, if there is still howling, then pass Equalizer elimination. Key points of operation: Be sure to control the level so that the howling can be maintained at a stable level and then adjusted to be more accurate. The operation must be slow, otherwise the correct howling points cannot be found one by one. The resonance points in the room are generally around 5-6 points. If there are too many feedback points, you need to check whether the placement of the speakers is reasonable.

　　2. Main expansion system

　　After debugging the monitoring system howling point, adjust the main expansion system in the same way. If the main expansion is a two-channel system, first close a channel, push the input fader of the mixer, and gradually increase the volume to find the howling point. After adjusting one channel, turn off this channel and adjust the other. After adjusting both sides, push the two channels up at the same time, check whether there are other howling points, and then eliminate them through the equalizer.