In the audio system, the frequency divider is an important part for the normal and effective operation of the speaker. Because the dynamic speaker increases its sound output power, due to its structural characteristics, its frequency coverage narrows. In order to achieve the full frequency band For high-power sound reproduction, speakers must be divided into frequency bands and then combined to play sound. Frequency division is to divide the signal into two or more frequency bands. It can make all kinds of speakers in the speaker system work in the best frequency range. Internal, thereby improving the working efficiency of the power amplifier, reducing the frequency distortion of the speaker, and realizing the purpose of reproducing the sound signal with high fidelity. According to the signal frequency band, the output signal frequency band can be divided into two frequency division, three frequency division and four division Frequency, the circuit or audio equipment used to achieve the frequency division task is called a frequency divider. According to the different position of the frequency divider, it can be divided into two types: power divider and electronic divider. This article first introduces why to use the electronic divider, and secondly explains the working principle, function and characteristics of the electronic divider Finally, the adjustment method, precautions and development trend of the electronic crossover are introduced.
Our sound engineer studies electroacoustics and the current development of electroacoustic equipment and technology is for one purpose: to reproduce all kinds of sound sources as faithfully as possible. The reproduction of sound technology is not realistic and almost impossible. As we all know, the frequency range of sound is between 20Hz and 20000Hz. Now the frequency range of most pre-level audio processing equipment can reach this width, but the current speaker has become a bottleneck part. We want to use one or It is difficult to broadcast sounds with a wide frequency close to 20Hz--20000Hz with a few speakers, because the effective operating frequency range of a single speaker is not very wide. In view of this, electro-acoustic engineers have designed speakers that work in different frequency bands, such as:
1. Subwoofer: Let it work in the frequency range of about 30-200Hz.
2. Low midrange speaker: 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 bands to configure a sound system that can maximize the true sound frequency (20Hz--20000Hz). Of course, the composition and parameters of different speaker equipment are different. What I said above is a three-way frequency system as an example. In practice, there are other systems such as: 2 frequency division or 4 frequency division, and different sound systems. Because the speakers used will be different, the working frequency of these speakers may not be the same, but the general principles and ideas are the same.
Then there is a question: 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 crossover came into being. It can provide a suitable frequency band according to the needs of different speaker operating frequencies, for example:
1. We can use the electronic crossover to send high-frequency signals to the tweeter through the power amplifier.
2. You can use the electronic crossover to send the intermediate frequency signal to the midrange speaker through the power amplifier.
3. You can use the electronic crossover to send the low-frequency signal to the woofer through the power amplifier.
In this way, the high, medium and low frequency signals are independently output and do not interfere with each other. Therefore, the advantages of different frequency bands of different speakers can be exerted as much as possible, so that the sound reproduction of each frequency band in the sound system is more balanced, the sound is more layered, and the tone is more perfect. This is why we use electronic crossovers.
The electronic frequency divider uses various types of active filters (high pass, low pass, band pass) to divide the audio signal in the full frequency domain into different frequency bands. The active filter is composed of a passive RC filter network and an operational amplifier. The composition of the follower, the attenuation characteristics increase with the increase of the RC order (for each increase of the order, the attenuation slope increases by -6db / out).
The electronic frequency division method makes only the power transmission line between the power amplifier and the speaker. There is no other link that affects the sound quality, which reduces the distortion and improves the damping coefficient of the power amplifier to the speaker. Since the load of the electronic crossover is the input of the power amplifier, the impedance is high and stable, so the crossover point can be easily adjusted And control the frequency division accuracy, and because the bandwidth of each frequency band of the electronic frequency divider is narrow, the higher harmonics caused by nonlinear distortion are suppressed, the total harmonic distortion and intermodulation distortion are reduced, and the electronic frequency divider overcomes The shortcomings in the power divider, but increase the cost and difficulty of system debugging, so they are mostly used in professional occasions.
1. Working principle diagram of two-frequency electronic divider
7-32 shows a block diagram of a two-way electronic frequency divider using a filtering operation synthesis method. The basic principle is to use a set of high-pass or low-pass filters to filter out the signals in the corresponding frequency band, and then invert this signal, and The input signals of the full screen are added to obtain a signal of another frequency band.
2. The working principle of the three-way frequency divider
The three-frequency circuit uses a filtering operation synthesis method. On the basis of the two-frequency circuit, as long as the signals output by the high-pass and low-pass filters are inverted and added to the full-band signal, the intermediate frequency output signal can be obtained.
Figure 7-33 shows a block diagram of a three-band electronic crossover using direct filtering. Its working principle is to input full-frequency signals into high-pass, band-pass, and low-pass filters to obtain corresponding high-, medium-, and low-frequency signals.
1. Basic crossover task
Because there are many kinds of speakers now, what kind of function and function should be used in the system, and the electronic frequency divider of a few frequency division still needs to be flexibly configured. The electronic frequency divider that is usually used now has frequency division 2, frequency division 3, frequency division 4 Equal distinction, more than 4 frequency division is too complicated and meaningless. Of course, the current electro-acoustic technology is changing rapidly. At present, there are still some frequency dividers that can perform other aspects of audio signal processing at the same time, but no matter what type of electronic frequency divider, the main functions and tasks are of course still frequency division
2. Protect speaker equipment
We know that the working frequency of different speakers is different. Generally speaking, the louder speakers have better low-frequency characteristics and lower frequency dive. It seems that under the same circumstances, the bass effect of the 18-inch speaker is generally better than that of the 15-inch speaker; on the contrary, the mid-range part will use a smaller caliber speaker, because usually the diameter of the paper cone vibration speaker The smaller the sound, the higher the frequency of the sound; so the vibrating diaphragm of the high-pitched part should also be very small in order to produce a high-frequency sound. Now that speakers are so complicated and so diverse, how to ensure that they can work safely and effectively is 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-high speakers in the system are not divided by the electronic crossover, but directly use the full-band audio signal, then these mid-high speakers will be easily damaged under the impact of low-frequency signals. In addition to the frequency division task, the more important function of normal use of it is: protection of speaker equipment.
3. Increase the level of sound
If there are many different types of speakers in an audio system, and indeed no electronic crossover is used, all types of speakers use full-frequency signals without frequency division, then there will be many frequencies superimposed and repeated between different speakers. In part, the acoustic interference will also become very serious, the sound will become blurred, the sound field will be very poor and the microphone will easily produce acoustic feedback. If an electronic crossover is used for a reasonable frequency division, the different speakers are in the best working state, so that the frequency range of the sound emitted by different speakers will hardly repeat, which reduces the phenomenon of sound waves interfering with each other , The sound will become more clear, and the sound will be better and more layered!
Adjustment method of electronic frequency divider1. 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 critical. Generally, it is more appropriate to adjust the position at 12 o'clock similar to the clock, 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 subwoofers in the system. Generally, it is adjusted at the positions of 12 o'clock and 14 o'clock similar to the clock. At the same time, pay attention to whether the LOW-MUTE bass volume mute button is pressed, otherwise no bass signal will be 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, according to the on-site effect. Sometimes the bass sounds too hard and too thin, we can turn it on to add a delay to the bass, which can increase the fusion of bass Degree and fullness; on the contrary, if you think the bass is suitable, don't turn it on, otherwise the bass will appear muddy and muddy. Generally adjust the position 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 sound system. In the 2-way frequency operation mode, it is usually adjusted in the range of 180Hz-250Hz. That is to adjust the position at 10 o'clock and 11 o'clock similar to the clock.
6. HIGH-LEVEL: knob for adjusting the volume of treble output. The adjustment of the treble output volume should be determined according to the crossover point and the number of middle and high tweeter speakers in the system. Generally, it is adjusted at the position of 12 o'clock and 14 o'clock similar to the clock. At the same time, pay attention to the fusion of treble and bass: when the treble is too small, the bass surround sound will appear dim; if the treble is too large and too prominent, it will appear out of touch with the bass and will not merge. It's just moderate.
1. Crossover point: In a 2-way audio system, the adjustment of the crossover point does not actually depend on the subwoofer, but on the mid-range and tweeter speakers. Because the subwoofer can work below 300Hz, but some mid-high speakers have a small caliber, and the dynamic range is not large enough. They must work above 200Hz to ensure their safety. It's very dangerous to work the mid-high speakers.
2. Volume control: no matter the input level or output level, there must be a degree when adjusting, do not open too much. If the volume knobs on the electronic crossover are all turned up 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 below the electronic crossover The attenuation switch is on. Pay special attention to this, otherwise the signal in the electronic crossover will be distorted and it is easy to damage the lower-level equipment.
3. Some electronic crossovers have one: X10 button, please be careful not to press it easily. For example, if our crossover point is adjusted at 200Hz, press this button 200 X 10 will become 2000Hz, so unless you need it, otherwise do not press this button.
4. Some electronic crossovers have a choice of bass mode on the rear panel, which can synthesize two stereo signals into one output, which can reduce the acoustic interference between the subwoofers. Everyone can use it appropriately. Of course, if the bass crossover frequency is higher, then the sound from the subwoofer will have a certain directivity. At this time, it is still better to work 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 mostly divided by 2. Considering flexibility and versatility, the rear panel of these electronic crossovers will generally have A stereo and mono working mode switch, if you put this switch in mono working mode, then this electronic crossover will change from a two-channel two-way electronic crossover A single-channel electronic divider with a frequency divider of 3 is now available. Therefore, unless necessary, don't easily switch this working switch, otherwise the frequency signal output from the signal output port behind the electronic crossover will be very different! The lighter ones deteriorate the sound quality, and the heavier ones will damage the equipment!
6. The output of the bass signal in the system and the output of the mid-high sound signal must not be confused, otherwise the high-frequency signal will be given to the subwoofer, and the low-frequency signal will be given to the tweeter. Because the frequency is not right! The speaker will burn out if you do it right!
7. Whether the main speaker is divided by frequency: It is said whether the main speaker should pass through the electronic crossover. Everyone should have their own opinions. If you do n’t understand it, you can make multiple comparison tests and decide before you know. Don't make decisions blindly.
8. When using a digital processor to divide the frequency, it must be clear which is the frequency division point and which is the operating frequency range. In addition, there is a choice of frequency attenuation strength at the beginning and end of the operating frequency range, such as 6dB, 12dB, 24dB, 48dB, several options, we have to use flexibly, generally 24dB is more appropriate .
Although the frequency divider currently used 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 newly released. These digital processors basically have the function of frequency division. At the same time, the frequency division is displayed in digital form. It is clear at a glance, and it makes people understand and the accuracy of frequency division. The signal-to-noise ratio of the sum signal is greatly improved. What is more important is that these digital frequency division methods are different from the previous electronic frequency dividers. We take the dbx 260 digital speaker processor as an example for comparison. If we need to build a high-end audio system with a four-way frequency division, the 2 channel After the standard full audio signal is input to the dbx 260 digital speaker processor, we can divide it into four frequency bands for different speakers to work:
1. The first channel of the output signal of the dbx 260 digital speaker processor is provided to the subwoofer. The operating 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 subwoofer. The operating 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-midrange speakers. The operating 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 to the middle and high-frequency speakers. The operating frequency range is set at 750Hz-20000Hz, and the crossover point is set at about 2000Hz.
You can find that using digital processing can set an optimal operating frequency range after setting a crossover point. Such an accurate crossover cannot be done by analog circuits in electronic crossovers anyway. Of course, the working frequency range and crossover point in the above example are not fixed, and fine adjustments should be made according to the speaker and sound field. But through the above example, everyone should understand that the digital era of professional audio will come sooner or later. As our sound engineers, we must constantly learn and master the latest electro-acoustic technology. It is impossible to stand still!
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