After the sound system is electrified, it needs further careful adjustment and debugging. Generally, with the help of some special instruments and equipment, these debugging tasks can be completed well. Commonly used instruments and equipment mainly include: audio signal generator, millivoltmeter, noise generator, sound level meter, real-time spectrometer; When reverberation needs to be measured, a level recorder is also needed.
1, microphone phase calibration
Generally speaking, the microphones used at the same time in the sound system should be in phase. Before the project is delivered, the phase of all microphones in the system should be corrected to be in phase. When individual microphones need reverse connection due to special needs, you can use the reverse switch on the console or insert a "reverse line". The method of testing microphone phase is very simple. If the two microphones are in phase, the volume will increase obviously when pointing to the same sound source. If the two microphones are in opposite phases, the volume will decrease when they are used at the same time. In the process of adjustment, you can choose any microphone as a benchmark, and use it to compare all microphones in the system. The ones with the same phase belong to one category, and those with different phases belong to another category. Phase adjustment can be achieved by adjusting several types of microphones, that is, inserting 2-pin and 3-pin connections and exchanging them.
2. Adjustment of room equalizer
Generally, the room equalizer can be adjusted accurately with the help of pink noise generator and real-time spectrum analyzer. The room equalizer is mainly used to correct and compensate the room frequency characteristics. Therefore, it is necessary to ensure the consistency between the hall environment and the actual listening environment when debugging. In addition, the adjustment of room equalizer sometimes needs to be combined with the adjustment of speaker layout.
The room equalizer compensates the ambient frequency characteristics by changing the frequency characteristics of the signal. The change of frequency characteristics will inevitably lead to the change of phase characteristics and phase distortion. When the adjustment amount of the room equalizer is too large, especially in the narrow frequency band, it is necessary to use a large adjustment amount to achieve the equalization effect. Although the frequency characteristics of the room have been corrected, the sense of hearing will become poor due to phase distortion, which will be more prominent for stereo systems. In the case of poor sound construction conditions, the adjustment of room equalizer can sometimes only compromise between frequency characteristics and auditory experience. Forcing the frequency characteristics to be flat sometimes backfires. The best way is to improve the acoustic characteristics of the room itself.
(1) debugging process
① Pink noise, as the input test signal of the system, is obtained from white noise through -6dB/OCT filter. Compared with white noise, pink noise has higher low-frequency energy. Because the energy distribution of pink noise is close to the real music signal, it is often used as a test signal for audio engineering and audio equipment. The power capacity of speakers is generally measured by pink noise. If there is no pink noise, you can also play pink noise on CD records with pink noise. Generally, the frequency response of CD players above midrange can be 2 OHZ ~ 20 KHz+0.5 dB, which can meet the test requirements.
② Input pink noise into the mixer, and adjust the mixer to the standard output level, usually OVU, and the output level is +4dB. It should be noted that at this time, the equalizer EQ on the mixer is set to a flat line, that is, it is all set to zero, which will neither increase nor decrease the frequency of each segment of the test signal. The frequency adjustment potentiometers at each point of the room equalizer are also temporarily set to zero. Slowly increase the power amplifier volume regulator to hear the pink signal sound, and monitor it with a sound pressure meter until the sound pressure level of the powder noise signal in the hall reaches about 85dB.
③ Place the measuring microphone in the center of the hall, and put the selector switch on the spectrometer in the "OCT" position (this position is the octave filter position, corresponding to the characteristics of pink noise). At this time, the LED display on the real-time spectrometer is the frequency characteristic curve of the listening environment. The flatter, the better the frequency characteristics of room building sound.
④ Adjust the frequency enhancement/attenuation of each point on the equalizer to make the frequency characteristic curve on the spectrometer become a straight line.
After the above debugging, it is generally necessary to "smooth" the equalization curve on the equalizer, mainly to prevent excessive phase distortion when the equalizer is adjusted to sawtooth frequency characteristics.
(2) Adjustment point of room equalizer
① In the low frequency band of about 20 ~ 50hz and the high frequency band above 14kHz, its frequency characteristics are unnecessary, especially in the low frequency band. Because it is difficult to extend the general speaker to 2hz, it is good to reach 40Hz. Forcing the low-frequency characteristics to be flat and improving the ultra-low frequency will make the speaker "out of control" because of the excessive extension of the low frequency, and the distortion will be aggravated.
② The adjustment of room equalizer should always consider the contradiction between flat frequency characteristics and minimizing phase distortion, and make a compromise consideration.
(3) If the frequency characteristics of acoustic environment have obvious peaks and valleys, we should consider changing the position of the speaker and try to change the acoustic characteristics.
④ The adjustment of the room equalizer is a very detailed work, which needs to be adjusted repeatedly before it can be finally set. This is because in the process of adjustment, it is often necessary to adjust the position and sound environment of the speaker, and the equalizer will contain each other when adjusting.
Objectively speaking, the function of room equalizer is limited, and the defects of acoustic environment cannot be completely solved by room equalizer. The smaller the average metric, the better the sound quality. Without the pink noise generator and real-time spectrometer, the audio signal generator can send the frequency signal of each point with the same amplitude to the system according to each frequency point on the selected room equalizer, and can test the sound pressure at the scene through the sound pressure meter and adjust it through the room equalizer. So that the input signal of each point frequency generates the same sound pressure level in the field. The actual effect of this debugging method is worse than that of using standard pink noise. Therefore, professional units should be equipped with pink noise generators and real-time spectrum analyzer as much as possible.
3. Debugging of electronic frequency divider
The debugging of electronic frequency divider can be divided into high frequency, intermediate frequency and low frequency, among which the frequency divider has different uses in the system and different debugging methods. If the frequency divider is only used to divide the bass speaker, let the bass speaker work alone, take the bass dividing point of the frequency divider between 150 ~ 300 Hz, adjust the gain of bass clearing appropriately, feel the bass volume is appropriate, then audition with the full-frequency system, and then balance the bass and full-frequency volume; If a frequency divider is used in an all-frequency system, it is required to accurately set the frequency dividing points of high, medium and low frequencies according to the parameters provided by the speaker manufacturer, and then repeatedly adjust the signal gain of each frequency band until the hearing of each frequency band is relatively balanced, and then make further fine adjustment with reference to the sound pressure measured by the spectrometer at each test point.
4, the adjustment of the delay device
The purpose of using delay device in sound reinforcement system is to prevent stress and echo and improve the clarity of sound besides producing some "special effects" of sound. The adjustment of delay for this purpose should be based on the principle of eliminating the time difference between direct sound and listeners radiated by different speakers. But in practical engineering applications, it is often not required to compensate this time difference to zero. First of all, this is difficult to achieve, because at a certain point, zero time difference is achieved, and there will still be time difference around. Secondly, it would be unnatural to completely compensate the arrival time difference of direct sound radiated by different loudspeakers to zero. Because the uniform distribution of sound pressure level is mainly realized by the enhancement of direct sound by the secondary reflected sound, the time difference between the secondary reflected sound and direct sound's arrival at the audience at this time reflects the sense of space in the hall. Of course, the time difference between the near-reflected sound with strong energy indicated by Haas effect and direct sound cannot exceed 50ms, otherwise the clarity will be greatly affected. Properly adjusted, you can get more realistic and natural sound effects.
5. Adjustment of pressure limiter
Debugging of the pressure limiter should be carried out after the above equipment in the system is basically transferred. Generally speaking, in engineering, the role of the voltage limiter is to protect the power amplifier and speakers, so that the sound changes smoothly. Therefore, when debugging, the compression start-up level should be set first, usually not too low, and the specific setting depends on the adjustment range and signal conditions of various voltage limiters; Secondly, you need to set the compression start and recovery time. Usually, the start-up time should not be too long, so as to avoid the untimely protection action. In order to protect the equipment, the shorter the startup time, the better. In order to keep a good sense of dynamic when listening, the recovery time should not be too short, so as not to destroy the acoustic effect. The compression ratio set in general engineering is about 4: 1. Generally speaking, the adjustment of these two parameters should be based on the specific situation of the program, and the listening sense is natural and the sound has not changed significantly. Pay special attention to the setting of noise gate in voltage limiter. If there is no big noise in the system, the noise gate can be closed. If there is some noise, the threshold level of the noise gate can be set low to avoid the intermittent phenomenon of the sound reinforcement signal; If the system is noisy, it should be analyzed from the aspect of construction technology, and it cannot be solved by noise door alone. Other settings can be determined according to different requirements.
6, the determination of sound pressure level in the hall
On the basis of the above debugging, the sound pressure level of the hall is measured with a sound pressure meter. The pink noise generator is used as the noise source, and several frequency points are selected for testing in high, medium and low frequency bands. The test goal is: on the premise of ensuring the best signal dynamics, the sound pressure of each point of the adjusted system should reach the design sound pressure level, and the equalizer and electronic frequency divider should be fine-tuned according to the conditions of each point in the high, middle and low frequency bands. If the sound pressure level results of each test point are quite different, that is, the sound field uniformity is not good, it should be carefully analyzed and improved accordingly. First of all, we should start with the construction technology of architectural decoration. If there are big defects in this aspect, which affect the sound field quality, feasible rectification measures should be put forward. If there are no obvious defects in decoration, the placement position, orientation and installation form of speakers should be analyzed, including the distance between speakers and buildings, installation position requirements between speakers, orientation and frequency characteristics of speakers, etc.