A frequency divider is an audio device that can divide a sound signal into several frequency bands. We know that the frequency range of the sound is between 20Hz and 20kHz, and it is difficult to use a single speaker to guarantee the sound of a wide frequency such as 20Hz and 20kHz, because it will be technically different. All kinds of problems and difficulties. Therefore, under normal circumstances, in order to ensure the frequency response and frequency bandwidth of the reproduced sound, in the professional category, high-bass separate speakers are used for playback, and when high-bass separate speakers are used for sound, It is necessary to use the frequency divider.
Reasons for using crossovers for high and low sound speakers
The so-called high-bass separate speaker means that the high-frequency part of the sound is played by a tweeter, and the low-frequency part is played by a bass speaker, rather than a single speaker to complete the entire audio frequency band. In professional speakers, the tweeter is generally a horn type speaker, and the woofer has various forms such as direct and airflow. Regardless of whether it is internal frequency division or external frequency division, the high-bass separate speakers must adopt the frequency division sound reproduction scheme. The main reasons are the following three aspects.
1. Make all kinds of speakers work in the most suitable audio segment
Speakers with different diaphragm sizes and materials have different optimal operating frequency bands. The louder the loudspeaker, the better the low frequency characteristics. Therefore, under the same conditions, the 18-inch bass effect is definitely better than the 15-inch bass effect.
The better the rigidity and brittleness of the diaphragm material and the lighter the quality, the better the high-frequency characteristics of the playback. Many tweeters use titanium film or indium film as the diaphragm material, just to improve their high-frequency characteristics; and the diaphragm of the woofer generally uses paper, carbon fiber, bulletproof cloth, and rubber (edge) materials to facilitate bass reproduction.
The frequency divider can be used to send high-frequency signals to the tweeter, and low-frequency signals to the woofer. The high-frequency and low-frequency signals go their own way, taking advantage of the working frequency band of their speakers as much as possible to ensure speakers of different working frequency bands Give full play to make the playback characteristics of each frequency more balanced and consistent.
2. Overcome the cutting distortion caused by the vibration amplitude of the speaker diaphragm with different frequencies
When the speaker sounds, the vibration amplitude of the bass sound is large and the vibration amplitude of the high sound is small. In theory, the vibration amplitude of the speaker cone is inversely proportional to the square of the frequency of the reproduced sound, that is, the same speaker diaphragm, under the action of the signal voltage of the same amplitude, the lower the frequency, the greater the amplitude, that is, if the frequency increases 10 times, the amplitude will be reduced by 10 times the square, that is 100 times.
If we use a loudspeaker to produce sound in a wide frequency range, due to the limitations of the mechanical properties of the diaphragm, it is very difficult to have a vibration with a very wide amplitude at the same time, which will inevitably cause the phenomenon of sound cutting distortion, so that the reproduced sound quality Subject to certain influences.
The study found that cutting distortion has the greatest impact on bass. When the bass speaker is delivering bass, as long as there are high-frequency components, it will inevitably lead to cutting distortion, causing the bass to tremble and tremble. Of course, the cutting distortion of the tweeter will also make the treble sound hoarse, but it will not affect the bass.
3. Reduce the phenomenon of sound interference between different speakers in the same speaker
For tweeters and woofers in separate high and low speakers, although their operating frequency bands are different, if the full-frequency signal is sent to the tweeters and woofers without frequency division, there will definitely be tweeters and woofers When the same sound is emitted at the same time, when the same sounds of different speakers meet, it is likely that sound waves interfere with each other.
People with a little common sense of acoustics know that once the phenomenon of sound interference occurs, there will be a series of problems such as comb filter effect and standing wave. These problems will affect the good reproduction of sound to varying degrees.
After setting the crossover circuit, the tweeter and woofer respectively obtain their own best working frequency band sound signal, and the frequency range of sound between them is almost not covered. Except for a small amount of interference in the crossover point and crossover area of ​​the speaker, the rest The interference phenomenon of frequency sound no longer exists.
There is a simple reason for the phenomenon of sound interference in the crossover point and crossover area. Since the crossover attenuation rate of the crossover cannot be infinite, in the crossover area, especially at the crossover point, the tweeter and bass The speaker will have the sound of the other party's frequency band at the same time, and the phenomenon of sound interference is inevitable. Therefore, the higher the crossover attenuation rate of the crossover, the smaller the crossover crossover area, and the smaller the sound interference from the speaker.
Divider classification
There are two major types of crossovers: one is the passive crossover (PassiVe Crossover), also known as the power divider; the other is the active crossover (AcTIve Crossover), also known as the electronic crossover.
1. Passive crossover
Passive frequency divider is a built-in frequency divider of the speaker, which is composed of capacitor and inductance filter network. Its characteristic is that the frequency divider network is set between the power amplifier and the speaker. This frequency divider divides the full frequency audio power signal directly from the power amplifier into bass and treble or bass, midrange and treble, and distributes the frequency-divided signal to the speakers of each frequency band according to different frequency bands. In the full-frequency high-frequency, low-frequency or high-frequency, middle-frequency and low-frequency active frequency division speakers, the passive frequency division circuit completes the frequency division task.
The advantages of passive frequency division are: first, the structure is simple, the cost is low, and the sound is installed together, no adjustment is required, and it is convenient to use; second, the system connection is easier, as long as the amplifier is input with a full-frequency signal, the amplifier and the speaker are connected Together, you can achieve full-frequency playback; third, fewer power amplifiers are required. Generally, one power amplifier can bring two full-frequency passive crossover speakers, so the system cost is lower.
The disadvantage of passive frequency division is: first, the frequency division network must bear a large amount of power and current added to the speaker, so a larger volume of inductance is used, and because the parameter of the inductance is directly related to the impedance of the speaker, the impedance of the speaker It is also a function of frequency, which deviates greatly from the nominal value, so the error is large and the calculation is difficult; secondly, after the power audio signal output by the power amplifier passes through the capacitor and inductor filter, it will inevitably be due to the nonlinearity of the capacitor and inductor Distortion, sound distortion is inevitable; third, the audio power signal output from the power amplifier will cause a loss of power signal every time through a capacitor and inductance device, so the passive crossover power signal loss is greater; Finally, the frequency division attenuation The rate cannot be made too high, generally up to 12dB / octave, and the interference in the crossover region is too large. This is because the passive divider increases the frequency division attenuation rate by adding capacitors or inductors, that is, the filter order , But increasing the number of capacitors or inductors means increasing signal distortion and power loss, and increasing the crossover attenuation rate The result is more problems.
As the name implies, passive frequency division is a kind of "helpless": the frequency division method, the full-frequency power signal output by the power amplifier has to be divided, and without division will cause a series of problems, so it can only be forced to divide the power signal. . In order to reduce the system cost, civilian speakers all adopt passive frequency division. Professional speakers are very different from civilian speakers in terms of requirements, listening subjects, and users. Therefore, in addition to passive crossover speakers, there are also active crossover speakers.
2. Active crossover
Active frequency divider is a device that divides the full frequency audio weak signal. It is generally composed of an active electronic circuit frequency division system. Its characteristic is that the frequency division system is located in front of the power amplifier and weakly divides the full frequency audio. Send the bass, treble or bass, midrange and treble signals to their respective power amplifiers, and then output them to the bass, treble or bass, midrange and tweeters respectively by the power amplifier. This method is called active frequency division because it works at In the case of weak signals, low-power electronic active filters can be used to achieve frequency division.
Each speaker unit of a passive frequency-divided speaker has its own power signal interface. Some high and low-separated speakers can have both active frequency division and passive frequency division. There are active frequency divisions behind these speakers (AcTIve) and passive crossover (Passive) transfer switches, some of these speakers are also equipped with a locking mechanism to avoid accidental dialing. When using the active crossover method, be sure to set the crossover mode switch to the "AcTIve" side, and connect the treble amplifier to the high (Hi2h) input and the bass amplifier to the low (Low) input.
There are many advantages of active frequency division. First, due to the use of weak signal electronic circuit signals for frequency division processing, the sound signal loss is small, the distortion is small, and the reproduction sound quality is good; second, the frequency division attenuation rate can be higher than that of passive frequency division. It is easy to reach 24dB / octave. The crossover crossover area is much smaller than the passive crossover. The interference between the high and low sounds in the crossover crossover area is basically overcome. The third is good adjustability. The acoustic index is high.
None of the shortcomings of active frequency division is related to sound quality. The main problems are: First, high cost and large investment. Because the active crossover method has high and low frequencies, separate power amplifiers are used for each channel, so many power amplifiers are used. For example, one-to-two distribution speakers need to be driven by two power amplifiers; the second is to add an electronic crossover, which makes the Increase the difficulty of use in connection and adjustment.
Use of frequency divider
As mentioned above, there are two types of crossovers: active crossover and passive crossover. The passive crossover is fixedly installed inside the speaker, and does not require the sound engineer to adjust it. The active crossover method has many problems such as the correct use of the electronic crossover, reasonable connection, and adjustment. Therefore, this article only focuses on Several main issues that should be noted in the use of the active crossover are discussed.
[page_break]
1. Panel and function keys
The front panel of the electronic crossover is shown in Figure 1. The functions of each function key, button and interface are introduced below.
(1) INPUTGAIN．
Enter the gain. Input signal level adjustment is generally placed at the rib B position.
(2) LF DELAY
Bass delay. Delay O-2ms (maximum 60cm) for bass.
(3) LF / HF GAIN
Low frequency / high frequency gain. Adjust the level of low frequency band and high frequency band.
(4) MUTE
Mute. Block signals in a certain frequency band.
(5) x-0VER PREQ
Crossover frequency (crossover point). When dividing by two, there is only one dividing point; when dividing by three, there are two dividing points.
(6) RANGE
Frequency range-o frequency range is selected between 90-900Hz or 900Hz-9kHz.
(7) MODE
Frequency division method. Choice of two-channel two-way crossover or mono three-way crossover.
(8) MONO BASS
Mono bass. In the two-channel stereo mode, you can select mono bass output.
(9) CD EQ
Constant pointing horn equalization. In the case of using a constant pointing horn (patent of the American EV company), the high-band characteristics can be made better.
(10) LIMITER
Limit button. The output signal gain limit adjustment is used to limit the excessive signal and protect the power amplifier speaker.
(11) THRESHOLD
Threshold selection key. Choose the limit threshold range, there are two choices of -6dB and + 18dBu.
The back panel of the electronic crossover is generally dominated by various interfaces, as shown in Figure 2, the role of each interface and function keys is introduced below.
(12) FUSE
Insurance and power outlets.
(13) SERIAL NUMBER
Product series number.
(14) HIGH / MID / LOW OUTPUT
High frequency / intermediate frequency / low frequency output interface. When the two-channel two-way frequency output, the high frequency and low frequency are output according to the frequency band above the interface: when the single-channel three-way frequency, the high frequency, middle frequency and low frequency are output according to the frequency band below the interface.
(15) POLARITY
Polarity (phase) key. Use this key to perform reverse phase adjustment.
(16) INPUT
Signal input interface. Input a full-frequency signal from this interface, and input the signal from the left channel in mono-way three-way frequency mode.
2. Several typical connection methods of frequency division
For the sound reinforcement system with different requirements, the connection method of the electronic crossover is also different. In actual application, which connection method to choose depends on different situations.
(1) High / low frequency divider
The connection method of the high and low frequency division is shown in Figure 3. Separate high-bass active crossover speakers are generally used in large and medium-sized playback places. The power ratio of the treble amplifier and the bass amplifier is between 3: 7 or 4: 6.
(2) High / medium / low three-way type
The connection mode of high, middle and low three-way frequency is shown in Figure 4. High-mid-bass split-type active crossover speakers are generally used in large-scale playback venues. The power ratio of treble amplifier, mid-range amplifier and bass amplifier is roughly 2: 3: 5.
(3) Full frequency / ultra-low type
The connection of full-frequency / ultra-low mode is much simpler than that of other crossover methods. The connection of its full-frequency channel is exactly the same as that of the non-active crossover method. The left and right channels (main output) of the mixer output signals to the sound reinforcement. The main channel of the system, the connection sequence and method of the peripheral equipment of the main channel are the same as the connection method and sequence of the main channel of the general sound reinforcement system, just send a signal from the group output of the mixer to the crossover (full frequency / super Low processor), the ultra-low signal is sent to the ultra-low power amplifier and speaker from the low-frequency (ultra-low) output interface of the frequency divider (full frequency / ultra-low processor), and the frequency division point of the frequency divider is generally set below 100Hz , As shown in Figure 5.
In addition to the above connection methods, there is also a method of directly connecting a full-frequency / ultra-low processor to form a full-frequency ultra-low system, as shown in FIG. 6.
According to the author. The first connection method is better than the second connection method. Let's analyze the unique advantages of the full-frequency / ultra-low connection scheme. From the analysis, we can know which of the two connection methods is better.
The full-frequency / ultra-low system is a widely used system at present, which solves the problems often encountered in sound reinforcement systems from several aspects.
First, it solves the problem of compatible playback of vocals and music. As you know, the lower limit of the fundamental frequency of vocals is about 130Hz. If there are too many bass components in the vocals, it will result in turbid sounds, which directly affects the clarity and intelligibility of the language. Bass components, to ensure that the listener can clearly understand the language and singing content; and the lower frequency of the bass of the music can reach 20Hz, if the bass component in the music is insufficient, it will cause insufficient bass fullness. When a system wants to broadcast human voice and music, there will be a contradiction in the bass, and the full-range ultra-low solution can solve this contradiction. When playing vocals, you can use the mixer to pull down the group output fader, and the ultra-low frequency is gone; when playing music, push the group fader together, the ultra-low frequency and full frequency exist at the same time, adjust the full frequency and ultra The ratio between low frequencies, you can get a satisfactory music effect. From this point of view, the connection scheme shown in Figure 5 does have advantages in terms of regulation.
Secondly, to a certain extent, the problem of low efficiency of passive frequency division is solved. The ultra-low part of the full-frequency ultra-low system adopts the active frequency division method. Since the ultra-low frequency accounts for more than half of the entire sound energy, sometimes it can even reach more than 70%. The ultra-low frequency part of the full-frequency sound is actively divided. This means that more than half of the sound energy is improved, and even if the treble part will be lost after using passive frequency division, it will not matter the overall situation.
Some people replace the frequency divider with an equalizer, connect the equalizer to the ultra-low channel, and the equalizer is attenuated above 100Hz. It is believed that this can completely replace the frequency divider. In fact, the bass effect of this connection is definitely not good, because even if the equalizer is used to attenuate the treble part to the bottom, it only attenuates the treble part by 12dB. There are still some high-frequency components sent to the power amplifier through the equalizer. The frequency converter is a low-pass filter, and the high-frequency part of the sound cannot pass through at all. The treble component leaked from the equalizer is amplified by the power amplifier and then sent to the woofer. As mentioned above, once the treble component is present in the woofer, it will inevitably cause cutting distortion, resulting in bass tremor and poor performance.
Thirdly, the active crossover mode has good subwoofer effect and strong adjustability. The ultra-low system adopts the active crossover method to not only improve the transmission efficiency of the bass, but also minimize the distortion of the bass, making the bass more rich and deep. Since the ratio of ultra-low to full-frequency can be adjusted arbitrarily according to actual needs, the connection between the bass and full-range parts can also be controlled by the sound engineer, the room for the bass effect is very large, and the adjustability of the sound is further improved.
3. Precautions for adjustment and use of electronic crossover
The front panel and function keys of the electronic crossover have been introduced earlier, but it is not always possible to adjust the crossover if you only know the function keys. The main problems encountered during the adjustment of the crossover are discussed below.
(1) Determination of crossover point
The crossover point is the dividing point between the high-pass, band-pass, and low-pass filters of the frequency divider. It is often expressed in terms of frequency, in Hz. The crossover frequency should be specifically determined according to the frequency characteristics and power distribution of the speaker unit or speaker in each frequency band. When the speaker is shipped from the factory, the manufacturer will calibrate the working frequency band and frequency division reference frequency of each speaker unit. Generally speaking, it should be determined according to the manufacturer's requirements Crossover point.
However, sound engineers often encounter such problems in use. Because of the loss of the manual, it is impossible to know the crossover point parameters of a certain speaker. This requires adjusting the crossover point according to the evaluation results of human ear listening. When adjusting the crossover point, you should carefully listen to the connection of the sound of each speaker unit, and adjust to the state where the crossover frequency band is not blank.
The crossover point of the full-range ultra-low subwoofer is generally adjusted to 100Hz. If the crossover point is too high, the sound will be distorted. Everyone may wish to do an experiment, mention the crossover point to 500Hz, the bass sound will definitely have a sense of jitter, this is the cutting distortion.
(2) Sub-band gain
Due to the sensitivity of the speakers and the power ratio of the power amplifier, the sound of each frequency band will definitely be strong and the sound of a certain frequency band will be weak. In this case, the sub-band gain of the frequency divider needs to be adjusted.
In most cases, the sound of too strong frequency band should be attenuated to avoid burning the power amplifier or speaker unit of this frequency band due to the excessive signal after boosting. You will find that many manufacturers design the cross-band gain of the crossover to only attenuate and not improve (such as the DOD crossover), that is, when the maximum position is mentioned, it is 0dB (no increase or attenuation), and the attenuation is minimal The position is negative infinity, which is to avoid equipment damage due to signal boost.
(3) Other adjustments
There are many other function keys on the crossover. The function of these function keys is often not valued by people. In fact, adjusting them to the correct state will definitely further improve the sound effect.
(a) LF DELAY (bass delay)
Separate high and low speakers are shown in Figure 7. In the high-bass separate speakers, because the high-bass speaker units are installed on the front plane of the speaker. The treble is generally a horn, and the pronunciation point is rear; the bass is a cone-shaped cone speaker, the pronunciation point is front, and when the speaker sends out the sound, the situation that the bass first reaches the listener and the treble first reaches the listener. If the bass comes first, because of the predominant effect of human ear listening, people will feel the problem of bass advance, dullness or insufficient sound clarity; if the bass is properly delayed, this problem can be solved.
(b) MOno BASS (Mono Bass)
Is it better to choose the mono mode or the stereo mode for the bass? According to the author, under the premise of the conditions, the bass should be made into the stereo effect as much as possible, for three reasons:
One is that the music bass is not mono but stereo, so in order to reproduce a true stereo bass, the stereo bass system should be used to play;
The second is the past view that the bass has no directivity, but modern speakers can already have a certain directivity, so of course the difference in their spatial location will be noticed by people;
Thirdly, according to the theory of physiological acoustics, people have a sense of localization of bass. Bass positioning mainly depends on the phase difference (time difference) of the left and right ears, so stereo bass and mono bass must be different for listeners.
(c) POLARITY (polarity or phase) key
Almost all crossovers have this type of button, but the letters are marked with Inv, out Phase and so on. This button is used to adjust the phase of the output signal. When the speaker has reversed phase, you should press this key. If you want to understand the effect of the reverse phase of the sound system on the reproduced sound and the method of judging the reverse phase.
Reference link: http: //
Parabolic Reflex Reflector,Parabolic Grow Reflector,Aluminum Lamp Reflector,Safety Lighting Covers
Yangzhou Huadong Can Illuminations Mould Manufactory Co., Ltd. , https://www.light-reflectors.com