Tips for using professional audio equipment IV - electronic frequency divider

Author: 　 From: 　 DateTime: 2022-06-24　 Hits: 6141　 【Font: T  T 】

In my last few articles, I briefly introduced the use skills of mixer, equalizer and voltage limiter. In this article, I want to share with you the use skills of electronic frequency divider.
In a set of audio system, the frequency divider generally refers to an audio peripheral device that can divide the audio signal in the 20hz-20000hz frequency band into appropriate and different frequency segments, and then send them to the corresponding power amplifier to promote the corresponding speaker. Because it is an electronic device used to process and distribute audio frequency signals, we usually call it: electronic frequency divider. I won't say more about the detailed functions and working principle of the electronic frequency divider. Here, I just focus on making some easy to understand introductions to some aspects that you pay more attention to or often feel confused. I hope it can be helpful to you!
1、 Why do we use electronic frequency dividers
Our sound engineers study electroacoustics and the continuous development of electroacoustic equipment and technology for one purpose: to faithfully reproduce all kinds of sound sources as much as possible. Of course, it is unrealistic and almost impossible to make full use of all kinds of sounds in nature. As we all know, the frequency range of sound is between 20Hz and 20000hz. At present, the frequency range of most front-end audio processing equipment can reach such a width, but the current speakers have become a bottleneck. It is difficult for us to use one or a few speakers to play and send sound with a frequency close to 20hz-20000hz, Because the effective working frequency range of a single horn is not very wide. In view of this, electroacoustic engineers have designed speakers working in different frequency bands, such as:
1. Subwoofer: let it work in the frequency range of about 30-200hz.
2. Low and medium tone Speaker: let it work in the frequency range of about 200-2000hz.
3. Tweeter: let it work in the frequency range of about 2000-20000 Hz.
In this way, we can use different types of speakers working in different frequency bands to configure a sound system that can be close to the real frequency of sound (20Hz -- 20000hz) to the greatest extent. Of course, the composition and parameters of different speakers are different. What I said above is to take a three frequency division system as an example. In actual use, there are other systems such as 2-frequency division or 4-frequency division. Moreover, the speakers used in different sound systems will be different, so the working frequencies of these speakers cannot be fixed and the same, but the general principle and idea are the same.
Then there is a problem: how can we flexibly allocate audio frequencies to these different types of speakers working in different frequency bands? In order to solve this problem, the electronic frequency divider came into being. It can provide appropriate frequency bands according to the needs of different speaker working frequencies, such as:
1. We can use an electronic frequency divider to send the high frequency signal to the tweeter through the power amplifier
2. An electronic frequency divider can be used to send the IF signal to the midrange speaker through the power amplifier.
3. The electronic frequency divider can be used to send the low-frequency signal to the subwoofer 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 working frequency band advantages of different speakers can be brought into play as much as possible to make the sound playback of each frequency band in the sound system more balanced, make the sound more hierarchical and make the sound color more perfect. This is why we use electronic frequency divider.
2、 Functions and characteristics of electronic frequency divider
Through the above introduction, you should have a general understanding of the electronic frequency divider. What are the functions, characteristics and even disadvantages of using the frequency divider? Based on years of work experience, I have summarized the following points:
（1） , function and characteristics
1. Basic frequency division task: because there are many kinds of speakers, the electronic frequency divider with what function and how many frequency divisions should be used in the system should be flexibly configured. The electronic frequency divider commonly used now can be divided into 2 frequency division, 3 frequency division and 4 frequency division. Exceeding 4 frequency division is too complex and meaningless. Of course, the electroacoustic technology is changing with each passing day. At present, some frequency dividers can also process audio signals in other aspects while dividing frequency, but the main function and task of any type of electronic frequency divider is frequency division.
2. Protection of speaker equipment: we know that the working frequencies of different speakers are different. Generally speaking, the larger the diameter of the speaker, the better the low-frequency characteristics and the lower the frequency dive. Just like in the same case, the bass effect of 18 inch speakers is generally better than that of 15 inch speakers; On the contrary, the speaker with smaller caliber should be used for the mid tone part, because generally, the smaller the caliber of the current paper basin vibrating speaker, the higher the sound frequency; By analogy, the vibrating diaphragm of the high pitched part should also be very small to make a high-frequency sound. Since loudspeakers are so complex and diverse, it is very important to ensure that they can work safely and effectively. The electronic frequency divider can provide the best working frequency required by different speakers, so that all kinds of speakers can work more reasonably and safely. Imagine this: if the tweeters in the system are not divided by the electronic frequency divider, but directly use the full frequency band audio signal, then these tweeters will be easily damaged under the impact of the low-frequency signal. Therefore, in addition to the frequency division task, the more important function of the electronic frequency divider is to protect the speaker equipment.
3. Increase the sense of hierarchy of sound: if there are many different types of speakers in a sound system, and indeed no electronic frequency divider is used, and different types of speakers use full frequency signals without frequency division, there will be many frequency superposition and repetition parts between different speakers, sound interference will become very serious, and the sound will become blurred, The sound field will also be poor, and the microphone will easily produce acoustic feedback. If the electronic frequency divider is used for reasonable frequency division, so that different speakers are in the best working state, the sound frequency range issued between different speakers will hardly repeat, so as to reduce the phenomenon of mutual interference of sound waves, the sound will become particularly clear, and the sound color will be better and more hierarchical!
（2） , shortcomings and deficiencies
1. Too many frequency division choices will lead to confusion: as the saying goes, advantages have disadvantages. Like other professional audio peripherals, electronic frequency dividers are not perfect. Sometimes more speakers in the system need frequency division, which will be very complex, because different speakers need different frequency division points and different working frequency bands, For the average sound engineer, when using the electronic frequency divider to divide the frequency under such circumstances, they will feel that they have no way to start. Therefore, careful adjustment is very important. At the same time, we can also use 4-frequency division as little as possible and adopt 2-frequency division or 3-frequency division. This can be simpler and make our adjustment ideas clearer.
2. The use of electronic frequency divider will lead to the decline of sound effect: Although the use of electronic frequency divider has many advantages, it also limits the efficiency of these speakers because it rigidly stipulates the working frequency range of different speakers, which does not give full play to it and wastes a lot of resources. For example, a double 15 inch full frequency speaker can make a normal and large sound without passing through the electronic frequency divider, but if it works at a frequency above 200Hz after being divided by the electronic frequency divider, the fullness and shock of the speaker will be lost, because the bass of the speaker is cut off by the electronic frequency divider. In the same case, we use the electronic frequency divider to cut off the high part of most bass speakers. Although the sound may be good, it is undeniable that the bass speakers also waste a lot of energy. It doesn't matter for a sound system with a large number of speakers and paying attention to timbre, but if the number of speakers in a sound system is small and doesn't pay attention to timbre, it's more realistic not to use an electronic frequency divider at this time.
3. Unreasonable frequency allocation will lead to equipment damage: it is said that the rational use of electronic frequency divider can protect the equipment. Similarly, electronic frequency divider is a double-edged sword. If it is not used properly, it will damage the equipment: for example, we send the high pitch signal from the electronic frequency divider to the bass speaker, because the bass speaker can not send such a high frequency sound, Therefore, the phenomenon at this time is that neither the tweeter nor the bass speaker will have sound. If some sound engineers do not see the reason, but blindly increase the volume of the front-end signal and the rear-end power amplifier, the result is that it is useless to increase the volume. At this time, it is also easy to damage the power amplifier, and if the level signal is large enough to be distorted, it is easy to burn the speaker. Don't think that there is no sound in the subwoofer. After all, there is a lot of current passing through the subwoofer coil at this time. The same is true for other speakers, so improper use of electronic frequency divider will damage the equipment. In the following pages, there will be an example in this regard for your reference.
3、 Introduction and adjustment method of function keys of electronic frequency divider
（1） Introduction to the function knobs in the electronic frequency divider
Different electronic frequency dividers have different adjustment knobs and parameters. The following is a brief introduction taking rane AC22 electronic frequency divider as an example:
Rane AC22 electronic frequency divider is a stereo frequency divider. Each single channel has 6 buttons or knobs from left to right, which are as follows:
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. The bass output signal level can be adjusted.
3. Low-mute: low volume mute button. Press this button to turn 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 fuller.
5. Low / high-frequency: frequency division knob. The frequency division point of the electronic frequency divider can be adjusted.
6. High-level: volume adjustment knob for treble output. The treble output signal level can be adjusted.
（2） Adjustment method of electronic frequency divider
1. Master-level: the adjustment of channel signal input level is very important, just like the adjustment of channel gain of mixer, the volume in the first step is very important. Generally, it is more appropriate to adjust at the position similar to 12 o'clock, and there is no need to make large adjustment.
2. Low-level: the adjustment of bass output volume shall be determined according to the frequency division point and the number of bass speakers in the system. It is generally adjusted at the position similar to 12 o'clock and 14 o'clock. During the same adjustment, 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: low volume mute button. Press this button to turn off the volume of low-level bass output. This is mainly to compare the effects of bass and treble. Of course, do not press it in normal use.
4. Low-delay: adjust the bass delay knob flexibly according to the on-site effect. Sometimes the bass appears too hard and thin, we can turn it on to add a sense of delay to the bass, so as to increase the integration and fullness of the bass; On the contrary, if you think the bass is appropriate, don't turn it on, otherwise the bass will appear turbid and muddy. It is generally adjusted at the position similar to 8 o'clock and 11 o'clock.
5. Low / high-frequency: frequency division knob. The frequency division point of the electronic frequency divider shall be adjusted according to the types and characteristics of speakers used in the audio system. In the 2 frequency division working mode, it shall be generally adjusted in the range of 180hz-250hz. That is, adjust the position similar to 10 o'clock and 11 o'clock.
6. High-level: volume adjustment knob for treble output. The adjustment of treble output volume shall be determined according to the frequency division point and the number of treble speakers in the system. It is generally adjusted at the position similar to 12 o'clock and 14 o'clock. At the same time, pay attention to the integration of treble and bass when adjusting: if the treble is too small and surrounded by bass, the sound will appear dim; If the treble is too big and prominent, it will appear out of touch with the bass. Moderate is good.
3、 Some problems in audio system frequency division
（1） Replace electronic frequency divider with equalizer
Not every sound system is equipped with a frequency divider. Of course, it is not necessary to use a frequency divider under any circumstances. If there are not enough speakers in a sound system due to cost constraints, we are reluctant to configure an electronic frequency divider. At this time, if there is redundant equalizer in the system, we can actually consider using professional 15 segment or 31 segment equalizer to replace the frequency divider, which can also increase the sound pressure of the system. The reason is simple: ideally, we only need the subwoofer to send out a frequency below 200Hz, but in fact, most subwoofers have no built-in frequency divider, and its actual frequency can be as high as more than 2000Hz. As we all know, human ears are most sensitive to sounds around 1000Hz, so we must feel much greater when listening to sounds below 2000Hz than when listening to sounds below 200Hz. The human ear feels the sound is loud, of course, that is, the sound pressure of the whole system increases. The specific adjustment method is: increase 50-200hz by 3 dB on the equalizer; 300-500hz without lifting and attenuation; From 500Hz to 2000Hz, it gradually attenuates in a slope. In fact, the frequency of about 2000Hz is basically attenuated by about 12 dB. The principle and intention of this adjustment method are well understood. I won't say much here. There are also advantages of using this method: it is convenient to adjust the sound field and maximize the efficiency of the bass speaker! Of course, this is only an emergency and helpless practice, which is not advocated academically.
（2） . serious consequences caused by improper use of electronic frequency divider
Last year, a super large bar in Changsha opened during the national day. The sound system used 16 single 12 inch full frequency main speakers, 22 double 18 inch subwoofer speakers and more than 20 other auxiliary speakers. However, a few days after opening, it was found that two single 12 inch speakers of the main speaker were broken. At first, the technicians there thought it was normal damage and replaced two new speakers, but then six 12 inch full frequency speakers were broken one after another in the inland one week. This was very abnormal, and there was no problem with other speakers except the 12 inch main speaker. Later, I helped to check the system and found that the electronic frequency divider was not used properly. I just raised the frequency division point of the frequency divider from 130Hz to 230hz. In this way, the problem was solved, and the bass effect was much better than before. In fact, the reason is also very simple: in this system, due to the need to take into account the vocal performance, a 12 inch full frequency main speaker with good performance of vocal performance is adopted. At the beginning, the frequency division point of the electronic frequency divider is 130Hz. What is the concept? In other words, the 44 18 inch speakers of the 22 subwoofers in the system can only emit sounds below 130Hz, which is really limited and a great waste of resources; The 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 in more than 200 H