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Use skills of professional audio equipment

2021-02-05 49
The frequency divider mentioned in a sound system generally refers to the ability to divide the audio signal in the 20Hz--20000Hz frequency band into suitable and different frequency bands, and then send them to the corresponding power amplifiers to drive the corresponding speakers. A kind of audio peripheral equipment. Because it is an electronic device used to process and distribute audio frequency signals, we usually call it: electronic crossover. I won’t say much about the detailed functions and working principle of the electronic crossover. Here I just focus on making some easy-to-understand introductions to some of the aspects that people value or are often confused. I hope it can be helpful to everyone!

1. Why do we use electronic crossovers
The research of electroacoustics by our sound engineers and the continuous development of electroacoustic equipment and technology are for one purpose: to reproduce various sound sources as faithfully as possible, and of course to make full use of the various sounds in the natural world. Acoustic technology reproduction is unrealistic and almost impossible. As everyone knows, the frequency range of sound is between 20Hz and 20000Hz. The frequency range of most pre-level audio processing equipment can reach this width, but the current speakers have become a bottleneck part. We want to use one or It is difficult for a few speakers to be able to send out a wide frequency sound close to 20Hz--20000Hz, because the effective working frequency range of a single speaker is not very wide now. In view of this, electro-acoustic engineers have designed speakers that work in different frequency ranges, such as:
1. Subwoofer: Let it work in the frequency range of about 30-200Hz.
2. Low and mid-range speakers: Let it work in the frequency range of about 200-2000Hz.
3. Tweeter: Let it work in the frequency range of about 2000-20000Hz.
In this way, we can use different types of speakers working in different frequency ranges to configure a set of sound systems that can be as close to the true frequency of the sound (20Hz--20000Hz). Of course, the composition and parameters of different speaker equipment are different. What I said above is a three-way system as an example. In actual use, there are other systems such as two-way or four-way, and in different audio systems Because the speakers used are different, the working frequencies of these speakers cannot be fixed and the same, but the general principles and ideas are the same.

Then there is a question: how do we flexibly allocate audio frequencies to these different types of speakers working in different frequency ranges? In order to solve this problem, an electronic crossover came into being, which can provide suitable frequency bands according to the needs of different speaker operating frequencies, such as:
1. We can use an electronic crossover to send the high frequency signal to the tweeter through the power amplifier.
2. An electronic frequency divider can be used to send the intermediate frequency signal to the midrange speaker through the power amplifier.
3. An electronic frequency divider can be used to send low frequency signals to the woofer through the power amplifier.
In this way, the high, medium and low frequency signals are output independently and do not interfere with each other. Therefore, the advantages of different speakers' working frequency bands can be used as much as possible to make the sound reproduction of each frequency band in the audio system appear more balanced, make the sound more layered, and make the tone more perfect. This is why we use electronic crossovers.

Second, the role and characteristics of electronic frequency divider

Through the above introduction, everyone should have a general understanding of electronic frequency dividers, so what are the functions and characteristics, and even disadvantages of using frequency dividers? Based on years of work experience, I have summarized the following points:


Use skills of professional audio equipment


(1) Functions and characteristics
1. Basic frequency division task: As there are many types of speakers nowadays, what kind of function and frequency division electronic frequency divider should be used in the system still need to be flexibly configured. The electronic frequency division commonly used now has 2 frequency division and 3 division. It is too complicated and meaningless to distinguish between frequency and frequency division by 4. Of course, the current electroacoustic technology is changing with each passing day. At present, there are still some frequency dividers that can also process the audio signal in other aspects while dividing the frequency. However, the main function and task of the electronic frequency divider is of course the frequency division. .
2. Protect the speaker equipment: We know that the working frequencies of different speakers are different. Generally speaking, speakers with larger diameters have better low-frequency characteristics and lower frequency dives. It seems that under the same circumstances, the bass effect of 18-inch speakers is generally better than that of 15-inch speakers; on the contrary, speakers with smaller diameters should be used in the midrange part, because the diameter of the current cone vibration speakers is usually The smaller the sound, the higher the frequency; and so on, the vibrating diaphragm of the high-pitched part should also be very small in order to emit high-frequency sounds. Since the speakers are so complicated and there are so many types, how to ensure that they can work safely and effectively becomes very important. The electronic crossover can provide the best working frequency required by different speakers, so that various speakers can work more reasonably and safely. Imagine: If the mid-to-treble speakers in the system are not divided by the electronic crossover, but directly use the full-band audio signal, then these mid- and high-frequency speakers will be easily damaged under the impact of low-frequency signals. Therefore, the electronic divider In addition to the frequency division task, the more important function of the normal use of the frequency device is to protect the speaker equipment.
3. Increase the level of sound: If there are many different types of speakers in an audio system, there is indeed no electronic crossover, and different types of speakers use undivided full-frequency signals. There will be many overlapping and repetitive parts of frequencies, acoustic interference will become severe, the sound will become blurred, the sound field will be poor, and the microphone will be prone to acoustic feedback. If an electronic frequency divider is used for reasonable frequency division, so that the different speakers are in the best working condition, so that the sound frequency range between different speakers will hardly be repeated, thus reducing the phenomenon of sound waves interfering with each other. , The sound will become extra clear, the tone will be better and more layered!

(Two), shortcomings and shortcomings
1. Too many crossover options can lead to confusion: as the saying goes, there are advantages and disadvantages. Like other professional audio peripherals, electronic crossovers are not perfect. Sometimes there are more speakers in the system that require crossover. It seems very complicated, because different speakers need different crossover points and different working frequency ranges. For the average sound engineer, using electronic crossovers under such circumstances will make them feel unable to divide the frequency. Start. Therefore, careful adjustment is very important. At the same time, we can also use 4 frequency division as little as possible, and use 2 frequency division or 3 frequency division method, which can be simpler and will make our adjustment ideas clearer.
2. The use of electronic crossover will cause the sound effect to drop: Although the use of electronic crossover has many advantages, it rigidly stipulates the working frequency range of different speakers, so the performance of these speakers is limited, and the performance of these speakers is not completely A large part of the resources was wasted by playing it out. For example: a double 15-inch full-range speaker can emit a normal and louder sound without the electronic crossover, but if it works at a frequency above 200 Hz after the electronic crossover, then this one The fullness and shock of the speaker will be gone, because the bass of the speaker is cut off by the electronic crossover. In the same situation, we also used the electronic crossover to cut off the treble part of most of the bass speakers, although the sound may be nice, but it is undeniable that the bass speakers also waste a lot of energy. This does not matter for a sound system with a large number of speakers and attention to tone. However, if the number of speakers in a sound system is small and the tone is not emphasized but only to be louder, then it is still more realistic to not use electronic crossovers at this time.
3. Unreasonable frequency allocation can cause equipment damage: The above said that the reasonable use of electronic frequency dividers can protect the equipment. Similarly, electronic frequency dividers are a double-edged sword. If used improperly, they will damage the equipment: The high-pitched signal from the frequency converter is sent to the bass speaker. Since the bass speaker cannot produce such high-frequency sound, the phenomenon at this time is that the tweeter and the bass speaker will have no sound. If some sound engineers do not look at the reason, and just blindly increase the volume of the pre-amplifier signal and the post-amplifier, the result is that no matter how loud the volume is, it is useless. At this time, it will be easy to damage the power amplifier, and if the level signal is so large that it is distorted, it is easy to burn the speaker. Don't think that there is no sound from the woofer. After all, there is already a large current through the woofer coil at this time. The same is true for other speakers, so improper use of electronic crossovers will damage the equipment. There will be an example of this in the following pages for your reference.

3. Introduction and adjustment method of electronic crossover function keys
(1) Introduction of each function knob in the electronic crossover
Different electronic crossovers will have different adjustment knobs and parameters. Take RANE AC22 electronic crossover as an example for a brief introduction:
RANE AC22 electronic crossover is a stereo crossover, each single channel has 6 buttons or knobs from left to right, in order:
1. MASTER-LEVEL: channel signal input level. The level of the input signal can be adjusted.
2. LOW-LEVEL: Volume adjustment knob for bass output. You can adjust the level of the bass output signal.
3. LOW-MUTE: Bass volume mute button. Press this button to cut off the volume of LOW-LEVEL bass output.
4. LOW-DELAY: Bass delay knob. The bass signal can be delayed to make the low frequency more fuller.
5. LOW/HIGH-FREQUENCY: Frequency division knob. The crossover point of the electronic frequency divider can be adjusted.
6. HIGH-LEVEL: Volume adjustment knob for treble output. You can adjust the level of the treble output signal.

(2) Adjustment method of electronic frequency divider
1. MASTER-LEVEL: The adjustment of the channel signal input level is very important, just like the adjustment of the mixer channel gain, the volume of the first step is very important. Generally, it is more appropriate to adjust it at a position similar to the 12 o'clock clock, and no major adjustment is required.
2. LOW-LEVEL: The adjustment of the bass output volume should be determined according to the crossover point and the number of bass speakers in the system. Generally, it is adjusted at the 12 o'clock and 14 o'clock positions similar to the clock. At the same time, please pay attention to whether the LOW-MUTE bass volume mute button is pressed, otherwise there will be no bass signal sent out.
3. LOW-MUTE: Bass volume mute button. Press this button to cut off the volume of LOW-LEVEL bass output. This is mainly to compare the effect of bass and treble, of course do not press it in normal use.
4. LOW-DELAY: The adjustment of the bass delay knob should be used flexibly and adjusted according to the on-site effect. Sometimes the bass seems too hard and thin, we can turn it on to add a bit of delay to the bass, which can increase the fusion of the bass On the contrary, if you think the bass is suitable, don’t turn it on, otherwise the bass will appear muddy and muddy. Generally adjusted at 8 o'clock and 11 o'clock similar to the clock.
5. LOW/HIGH-FREQUENCY: Frequency division knob. Adjust the crossover point of the electronic crossover according to the type and characteristics of the speakers used in the audio system. In the 2-way working mode, it is usually adjusted within the range of 180Hz-250Hz. That is to adjust the position similar to the 10 o'clock and 11 o'clock of the clock.
6. HIGH-LEVEL: Volume adjustment knob for treble output. The adjustment of the tweeter output volume should be determined according to the crossover point and the number of mid- and tweeter speakers in the system. Generally, it is adjusted at 12 o'clock and 14 o'clock similar to the clock. At the same time, pay attention to the fusion of the treble and bass when adjusting: the treble is too small to surround the bass and the sound will appear dim; the treble is too large and too prominent, and it will appear to be out of touch with the bass and not fused. Moderate is good.

Third, some problems in the frequency division of the sound system
(1) Use equalizer instead of electronic crossover
Not every audio system will be equipped with a crossover, of course, it is not necessary to use a crossover under all circumstances. If a sound system is not equipped with enough speakers due to cost constraints, it is even more reluctant to configure one. The electronic crossover. At this time, if there is an extra equalizer in the system, we can actually consider using a professional 15-band or 31-band equalizer instead of the crossover, which can also increase the sound pressure of the system. The reason is simple: Ideally, we only need the bass speakers to emit frequencies below 200Hz, but in fact, most bass speakers do not have a built-in crossover, and its actual frequency can actually be as high as 2000Hz. Everyone knows that the human ear is most sensitive to sounds around 1000Hz, so we must listen to sounds below 2000Hz to feel much louder than sounds below 200Hz. Human ears feel that the sound is louder, and of course the sound pressure of the entire system has increased. The specific adjustment method is: increase 50-200Hz on the equalizer by 3 dB; 300-500Hz does not do boost and attenuation; above 500Hz to 2000Hz becomes a slope and gradually attenuates, in fact, the frequency around 2000Hz will basically attenuate about 12 dB. . The principle and intention of this adjustment method are well understood, so I won't say more here. There is another advantage of using this method: it is convenient to adjust the sound field and maximize the effectiveness of the bass speaker! Of course, this is only an emergency and helpless approach, which is not recommended academically.

(2) Serious consequences caused by improper use of electronic crossover

Last year, a large bar in Changsha opened during the National Day. The sound system used 16 single 12-inch full-range main speakers, 22 dual 18-inch subwoofer speakers, and more than 20 other auxiliary speakers. However, a few days after the opening, it was found that 2 single 12-inch speakers of the main speaker were broken. At first, the technicians there thought it was normal damage and replaced 2 new speakers. However, they continued to break again within a week. I installed 6 12-inch full-range speakers, which is very abnormal, and there is no problem with other speakers except the 12-inch main speaker. Later, I helped to check the system and found that the electronic crossover was used improperly. I just increased the crossover point of the crossover from 130Hz to 230Hz, and the problem was solved, and the bass effect was much better than before. . In fact, the reason is very simple: this system has to take into account vocal performances, so a 12-inch full-range main speaker that performs better on vocals is used. At the beginning, the crossover point of the electronic crossover is 130Hz. What is the concept? What? That is to say, 44 18-inch speakers of 22 subwoofers in the system can only emit sound below 130Hz, which is really limited and wastes resources; while 16 12-inch speakers in the system have to bear the main sound above 130Hz , We know that the strength and shock of the sound are concentrated at about 200 Hz, so these 16 12-inch speakers are simply overwhelmed due to their small caliber. Such frequency division and use methods are tantamount to murder! The result can be imagined. After adjustment, it is quite different. The 16 main speakers only emit sound above 230Hz and sound below 230Hz.

The sound is in charge of 22 woofers, so that the two sets of speakers perform their duties, and the matching is more perfect, the key is to give play to their respective strengths. From the above example, we can clearly know how flexible it is to use an electronic crossover!

(3) About the connection of the main speaker and the electronic crossover
As you all know, the audio systems we use now generally have two-way systems. Under normal circumstances, the electronic crossover divides the suitable low-frequency signal and sends it to the subwoofer. Of course, the crossover point should be flexible. grasp. Then there may be another question that often plagues everyone: Does the main speaker go through the crossover or not? This confusion is similar to what I wrote in my last issue of the Compressor article: Is the compressor better in front of the equalizer or behind? My personal opinion is that the high-power main speakers are more flexible without the electronic crossover, because the main speakers are generally equipped with professional equalizers, and we can also flexibly adjust the low frequency part of the main speakers to make it better It works with the subwoofer; but if the main speaker passes the electronic crossover, if we set the crossover point at 200Hz, then the main speaker can only emit sound above 200Hz. Think about it, so then Isn't the woofer of a multi-main speaker a waste? For example, a slow shaker in Shantou area used 8 dual 18-inch woofer speakers and 10 dual 15-inch full-range main speakers. As a result, Party A always felt that the bass was not strong enough and did not want to add bass equipment. When I checked the system, I found that the 10 main speakers passed the electronic crossover. Since Party A said that the bass was not strong enough, the sound engineer divided the bass frequency very high, around 350Hz. Imagine this: Although this adjustment has increased by 8 The strength and loudness of the subwoofer, but let 10 double 15-inch full-range main speakers work above 350H, the main speakers can be said to basically not emit any bass. I immediately changed the lines of the 10 main speakers to direct control with an equalizer, and the effect immediately changed! The sound engineer there found it incredible: I just unplugged the two audio cable connectors and plugged them in another place. How could the effect be so different? Besides, he connects the main speakers according to the normal connection in the manual of the electronic crossover. It seems that I don't use the electronic crossover in this way to comply with the rules, right? I think you can calculate the reason: how much bass energy has been increased by liberating 20 15-inch speakers from 10 dual 15-inch main speakers! So you can't be rigid, you have to respect the facts and break the rules!
The above example is because the main speaker passed the electronic crossover, improper use caused serious damage to the main speaker of the system. Another example is because the main speaker has passed the electronic crossover, which is not suitable, and it also caused a serious shortage of system bass energy and overall sound pressure. It can be seen that sometimes some speakers must pass through the electronic crossover, some can pass or not, and some cannot pass. It seems to be self-contradictory, and everyone will feel very confused, so what should we do? In fact, it’s very simple. To sum it up, it’s best not to use electronic crossovers for dual 15-inch full-range main speakers; single 15-inch main speakers can be used flexibly; and single 12-inch main speakers are best to pass electronic crossovers. , It is safe to work above 180Hz.

Fourth, the development direction of electronic frequency dividers
Although the frequency divider we are currently using is called an electronic frequency divider, it is not digital after all. Its internal circuit is still analog, and the adjustment accuracy is not very accurate. In recent years, some digital processors have been released. Basically, these digital processors have the function of frequency division. At the same time, the frequency division frequency is displayed in digital form, which is clear at a glance, and the accuracy of frequency division The signal-to-noise ratio of the sum signal is greatly improved. More importantly, these digital crossover methods are different from previous electronic crossovers. We take the dbx 260 digital speaker processor as an example for comparison. If we need to build a four-way high-end audio system, After the standard full audio signal is input to the dbx 260 digital speaker processor, we can divide it into four frequency bands and provide it to different speakers:
1. The first channel of the output signal of the dbx 260 digital speaker processor is provided to the subwoofer speaker. The working frequency range is set at 30Hz-150Hz, and the crossover point is set at about 90Hz.
2. The second channel of the output signal of the dbx 260 digital speaker processor is provided to the bass speaker. The working frequency range is set at 130Hz-450Hz, and the crossover point is set at about 220Hz.
3. The 3rd and 4th channels of the output signal of the dbx 260 digital speaker processor are provided for low and midrange speakers. The working frequency range is set at 400Hz-800Hz, and the crossover point is set at about 500Hz.
4. The 5th and 6th channels of the output signal of the dbx 260 digital speaker processor are provided for mid- to high-pitched speakers. The working frequency range is set at 750Hz-20000Hz, and the crossover point is set at about 2000Hz.
You can find that the use of digital processing can set an optimal operating frequency range after setting a crossover point. Such a precise frequency division cannot be achieved by the analog circuit in the electronic frequency divider. Of course, the working frequency range and crossover point in the above examples are not fixed, and fine adjustments should be made according to the speakers and sound field. But through the above example, everyone should understand: the digital era of professional audio is coming sooner or later. As an audio engineer, we must continue to learn and master the latest electro-acoustic technology. It is not enough to stand still!

5. Problems that need attention when using electronic crossover:
1. Crossover point: If in a 2-way audio system, the adjustment of the crossover point does not actually depend on the bass speakers, but the mid- and high-range speakers. Because the bass speakers can work below 300Hz, but some mid-to-treble speakers have too small a speaker diameter and insufficient dynamic range. They must work above 200Hz to ensure their safety. If the crossover point is around 130Hz at this time, then these The mid-to-treble speakers are dangerous when they work.
2. Volume control: Regardless of whether it is input level or output level, there must be a degree when adjusting, and do not turn it on too much. If the volume knobs on the electronic crossover are turned on to a large extent, and the sound pressure of the system is not enough, then adjust the signal level in front of the electronic crossover or adjust the level and volume of the power amplifier under the electronic crossover Attenuation switch. Pay special attention to this, otherwise the signal in the electronic crossover will be easily damaged if the signal is distorted.
3. There is a button of X10 on some electronic crossovers. Please be careful not to press it easily. For example, if our crossover point is adjusted to 200Hz, pressing this button 200 X 10 will become 2000Hz, so unless it is necessary, generally do not press this button.
4. Some electronic crossovers have a bass mode option on the rear panel, which can synthesize 2 stereo signals into 1 output, which can reduce the sound interference between the low speakers. You can use it appropriately. Of course, if the bass crossover point is higher, then the sound from the subwoofer will have a certain degree of directivity. At this time, it should work better in the state of 2 stereo signals.
5. Stereo working mode and mono working mode: At present, most of the electronic crossovers we use are divided by 2. Considering flexibility and versatility, the rear panel of these electronic crossovers generally has A stereo and mono working mode switch. If this switch is placed in mono working mode, then the electronic crossover will change from a dual-channel 2-way electronic crossover to A single-channel 3-way electronic frequency divider. Therefore, unless necessary, do not easily switch this working switch, otherwise the frequency signal output by the signal output port behind the electronic frequency divider will be very different! The lighter ones deteriorate the sound quality, the more serious ones can damage the equipment!
6. The output of the bass signal in the system must not be confused with the output of the mid-to-treble signal, otherwise the treble signal is given to the woofer speaker, and the bass signal is given to the tweeter speaker. In this way, there is really no sound in the audio system. Because the frequency is wrong! Maybe it will burn out the speakers!
7. Whether the main speaker is frequency-divided: The above mentioned whether the main speaker needs to pass an electronic crossover. Everyone should have their own opinions. If you don’t understand, you can compare and test several times before deciding. Don't make blind decisions.
8. When using a digital processor for frequency division, be sure to distinguish which is the frequency division point and which is the operating frequency range. In addition, there will be a choice of frequency attenuation strength at the starting point and ending point of the working frequency range, such as 6dB, 12 dB, 24 dB, 48 dB, several options, we have to use it flexibly, generally 24 dB is more appropriate .

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