The 21st Guangzhou International Professional Lighting and Sound Exhibition (hereinafter referred to as the "Guangzhou Exhibition") is grandly opening today! This exhibition is located in Zone A of the Canton Fair Complex. The 13 exhibition halls and the Y channel exhibition area gather 1403 exhibitors from all over the world. The scale of the exhibition exceeds 130000 square meters, ranking first in the global professional audio-visual industry brand exhibitions. With the steady recovery of cultural and entertainment industries around the world, Guangzhou Exhibition has once again become a hub for cooperation and exchange in the global industry, helping industry colleagues to take the lead in grasping the cutting-edge technology and future development pulse of the professional audio and visual industry.
Exhibition address: B38, Hall 2.1, Pazhou Convention and Exhibition Center, Guangzhou
Soft start protection
When a high current absorbing audio device is powered on, the current flowing through it can reach 4-10 times its average current value, which is an impact on the power grid and the device itself. In severe cases, it can damage the device. At this point, the soft start circuit can suppress the influx of current at the moment of equipment switching, allowing it to smoothly achieve normal protection of the equipment and not cause fluctuations in the power grid. This function is usually realized by the Negative temperature characteristic of thermistor (NTC)
DC protection
When the output stage of the power amplifier is damaged or the static bias is offset, it is possible to transmit a DC signal. For speakers, their working mode only generates impedance for AC signals, and for DC signals, they do not generate any impedance (equal to zero impedance). At this point, the current is infinite, so the coil of the speaker is equivalent to a heating wire that will quickly burn out under DC signals. Therefore, accurate and fast DC protection circuits are very important. The DC protection activation value of the power amplifier is usually set at 2V. When it is greater than or equal to this value, the power amplifier will cut off the output to protect the speaker. Of course, there are also power amplifiers that will cut off the output by burning the built-in DC fuse
Short circuit protection
When a short circuit occurs at the output end of the power amplifier due to certain reasons, the current output by the power amplifier will cycle through its own circuit and become infinite. This situation is very dangerous, so it is necessary to have accurate and fast short-circuit protection circuits to protect the power amplifier equipment. Each power amplifier must have a short-circuit protection function, which is vital and cannot be ignored
Usually, when a short circuit occurs in a power amplifier, it first controls the input signal to reduce its amplitude or even zero. If the situation does not improve (the current flowing inside the power amplifier still exceeds the safety value), it will suppress the output current, making the current flowing inside the power amplifier always lower than the safety value of the output stage transistor
Overcurrent protection
When the load of the power amplifier is too low but has not reached the short-circuit state, the short-circuit protection will not operate, but the output current will be very large and exceed the safe use value of the power amplifier. At this time, the overcurrent protection circuit will intervene and work. The usual approach is to control the input voltage and output current to ensure that the power amplifier always operates within a safe range
Overheat protection
A well-designed power amplifier will not experience overheating protection under normal use, and will only operate when the external usage environment is harsh or internal faults occur. The hottest part of the entire power amplifier is the C-pole (collector) of the output stage transistor, so the temperature sensor for overheat protection is generally installed in the closest place to the C-pole of the transistor or the hottest place on the heat sink. The threshold for overheating protection is generally 95 ℃, and there are also 105 ℃. The extreme withstand temperature of the transistor is 105 ℃.
The sound system that picks up the microphone has the possibility of feedback howling. The harm of microphone whistling is significant, mainly manifested in the following aspects:
1. When self-excited, the power amplifier will produce a large power output, which may exceed the capacity of the sound reinforcement equipment and burn out the power amplifier and sound producing equipment.
2. When the feedback coefficient is close to 1, due to the comb filtering effect, the superposition between the delayed sound field and the direct sound field will cause the amplified sound field to be less than the original sound field
Narrowing in sound sense.
3. The delayed feedback of the speaker sound field will cause a series of delayed echoes throughout the entire system, and this echo will exacerbate the comb filtering effect, resulting in significant
Distorted reverberation, trailing sound, and just sound distortion.
4. The sound pressure output during whistling is very high, which seriously affects the atmosphere of various activities.
Eliminating feedback howling starts with the necessary conditions for generating feedback howling. As long as one of these conditions can be broken, the goal can be achieved. Here are the top 5 recommended by Guoshi
A method to eliminate microphone feedback howling
1. Eliminating microphone feedback howling using inverse cancellation method
Anti phase cancellation to prevent self-excitation is common in high-frequency amplification circuits. Two microphones of the same specification can be used in the audio amplification circuit to pick up direct sound and reflected sound, respectively,
By using a reverse phase circuit to cancel out the reflected sound signals before entering the power amplifier, it can effectively prevent self excitation of whistling
2. Adjusting the distance method to eliminate microphone feedback howling
One of the most effective ways to avoid whistling and increase the amplification volume is to pick up the microphone as close as possible to the sound source, while using a non directional microphone. here
To be clear, directional microphones (especially sharp directional microphones) have very little pickup attenuation from distant sound sources. Adjusting the distance plays a role in increasing the amplification volume and preventing whistling
Not big. Whether the sound reinforcement system is prone to howling is not directly related to the sensitivity of the microphone. However, highly sensitive microphones are highly directional and prone to squealing
It's just that. Shortening the distance between the sound equipment and the audience can actually improve the loudness of the amplification. The total gain of the system can be appropriately reduced. If accompanied by broad directional
A near field speaker, with the microphone slightly away from the speaker, can avoid howling
For the direct feedback sound field of speakers, the farther the microphone is from the speaker, the better, and the closer the speaker is to the audience, the better. The microphone should be placed in the radiation direction of the speaker
On the back, if the microphone is likely to be carried around, the speaker should be placed in a place where the microphone cannot be very close
3. Phase modulation method to eliminate microphone feedback howling
The self-excited howling of the amplifying system has a positive feedback loop. If the microphone signal is phased, it will disrupt the phase condition of self-excited howling, thereby preventing the system from self excitation
Screaming. There is data indicating that the stability is best when the phase deviation value is 140 °; Moreover, the higher the modulation frequency, the better the stability of the system. To facilitate processing
The subsequent sound quality does not experience significant distortion, and the maximum allowable value of its phase modulation frequency is 4Hz. Finally, after adjusting various equipment, never let others move around,
Including some DJs who are not familiar with equipment performance and only know how to turn it on, off, and adjust the volume
4. Feedback suppressor method (narrowband notch method) to eliminate microphone feedback howling
For the multifunctional hall sound reinforcement system, the main consideration is to ensure that the language transmitted by the sound reinforcement system is clear and understandable, the music is clear and warm, and is not affected by noise interference. At the same time, it should also ensure excellent frequency response width and minimal distortion response under the condition of uniform and consistent sound field. Therefore, the selection of speaker systems is of utmost importance.
All signals in the audio system, except for the target signal, are noise, but the signal and noise coexist relative to each other and complement each other. When the signal is different from each other, noise will inevitably be generated, but noise may not necessarily be caused by different ground conditions. To eliminate the noise in the sound reinforcement system, let's first take a look at the relationship between ground and signal:
Ground and signal are commonly referred to as reference and target objects. The signal ground is the reference object of the signal, and grounding usually refers to being connected to the ground, but in a sound reinforcement system, it has nothing to do with the ground. It is a reference object set in the system, and grounding is essential. It may seem simple, but it is actually quite complex. According to its different functions, it can be divided into two categories: functional grounding and protective grounding. Functional grounding includes the following four categories.
(1) Working grounding, also known as system grounding, is to ensure the normal operation of the system, prevent system oscillations, and ensure the reliability of equipment in the system. It is usually necessary to install a grounding at an appropriate location, so that the individual equipment can operate on the basis of that grounding. As usual, the grounding wire of a 220V power supply is taken from the neutral point of the transformer.
(2) Logic grounding is a grounding set to obtain a stable reference potential, also known as the DC neutral point.
(3) Shielded grounding is a grounding system installed to prevent the impact of electromagnetic induction on the system. It is the most complex of all grounding systems, as it not only prevents interference from others, but also prevents interference from others. The higher the interference frequency, the denser the metal mesh used for shielding, otherwise the effect will not be achieved.
(4) Signal grounding is installed to ensure a stable reference potential, which is the reference object mentioned earlier.
In a sound reinforcement system, the logic grounding, signal grounding, and shielding grounding are organically combined through the ground terminal of the signal line, so that the system equipment operates at a unified potential. It should be emphasized that the signal input and signal output terminals of the same equipment cannot be connected together, and the output ground of the previous stage can only be connected to the input ground of the subsequent stage, otherwise the signal may float through the ground wire feedback. Of course, it is difficult to completely eliminate noise. We can only try to control or reduce the voltage of noise as much as possible, improve the signal-to-noise ratio of the system, and prevent noise from forming interference.
In the process of professional sound engineering construction for clients, we always encounter various difficulties. Therefore, the editor has summarized some common problems and introduced them to everyone. The following are the specific contents:
1. Signal allocation issues
In professional audio engineering projects with several sets of speakers, the signal is generally distributed to multiple amplifiers and speakers through a single equalizer. But at the same time, it also leads to the mixed use of various brand models of amplifiers and speakers, which may cause various problems in signal distribution, such as whether the impedance matches, whether the level distribution is average, whether the power obtained by each group of speakers meets the standard, etc. Additionally, it is difficult to adjust the frequency characteristics of the sound field and speakers with a single equalizer.
2. Debugging issues with the graphic equalizer
Common graphic equalizers can have three types of spectral wave shapes: swallow shaped, mountain peak shaped, and wave shaped. The above spectral wave shapes are artificially imagined by professional sound engineers, but they are not actually the spectral wave shapes required for actual sound engineering sites. As is well known, the ideal spectral wave shape curve is relatively stable and flat. If the spectral wave shape curve is artificially adjusted through imagination, it can be imagined, The ultimate effect is often counterproductive.
3. Pressure limiter adjustment issue
In professional audio engineering, the common problem with adjusting the pressure limiter is that the pressure limiter does not work at all or excessive action can lead to a reaction. The former can still be used after problems occur, while the latter can seriously affect the operation of the sound engineering system. The specific performance is usually manifested as the stronger the accompaniment sound, the weaker the human voice, and the performer is at a loss.
4. System level adjustment issues
Firstly, the sensitivity control knob of the power amplifier was not in place, and secondly, the audio system did not perform zero level adjustment. In some cases, when the Mixing console channel pushes upward slightly, the sound output will increase a lot, which will affect the normal operation and fidelity of the audio system.
5. Bass signal processing
The first type of problem is to directly use the full frequency signal to drive the speaker of the power amplifier without electronic frequency division; The second type of problem is not knowing where to obtain the bass signal from the system for processing. If you do not perform electronic frequency division and directly use a full frequency signal to push the speaker to the power amplifier, although the speaker can emit sound without damaging the speaker unit, it can be imagined that the low unit can emit full frequency sound alone; But if the bass signal is obtained from an inappropriate position in the system, it can also bring unnecessary trouble to the sound engineer's on-site operation.
6. Effect loop processing
The post signal of the pusher should be taken to avoid the microphone howling scene caused by the effect being out of control. If conditions permit, one channel can be occupied when returning, making it easier to adjust.
7. Line connection processing
In professional audio engineering, the common issue of high communication interference in audio systems is due to inadequate wiring connections. There are also balanced to unbalanced and unbalanced to balanced connections in the system, which must comply with regulatory standards when used. In addition, it is prohibited to use inferior connectors in professional audio engineering.
8. Control issues
The console is the control center of the audio system, and sometimes a significant increase or decrease in EQ balance between high, medium, and low on the console indicates that the audio system is not set correctly and should be re debugged. Excessive adjustment of the EQ on the console is prohibited.
