A frequency divider is an acoustic device that divides a sound signal into frequency bands. We know that the frequency range of the sound is between 20Hz and 20kHz. It is hoped that using only one speaker will ensure that a wide frequency sound such as 20Hz-20kHz is difficult to achieve, because this will be technically different. A variety of problems and difficulties. Therefore, under normal circumstances, in order to ensure the frequency response and the frequency bandwidth of the reproduced sound, in the professional range, the high-bass split speaker is mostly used for sound reproduction, and when the high-bass split type speaker is used for sound transmission, It is necessary to use a frequency divider.
Reasons for using a crossover for high and low sound split speakers
The so-called high-bass split speaker refers to the speaker that plays the high-frequency part of the sound by a tweeter, and the low-frequency part is played by a subwoofer, instead of the task of playing the entire audio band by one speaker. In professional speakers, the tweeter is generally a horn speaker, and the woofer is available in direct and airflow. Regardless of whether it is internal or external, the high and low sound split speakers must adopt a crossover and playback solution. The main reasons are as follows.
1. Make all kinds of speakers work in the most suitable audio segment
Speakers with different diaphragm sizes and materials have different operating bands. The louder the speaker, 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, the lighter the quality, and the better the high frequency characteristics of the sound reproduction. Many tweeters use titanium film or indium film as the diaphragm material to improve their high-frequency characteristics. The diaphragm of the woofer generally uses materials such as paper, carbon fiber, bulletproof cloth and rubber (edge) to facilitate bass reproduction.
The frequency divider can be used to send high-frequency signals to the tweeters, and the low-frequency signals are sent to the woofer. The high- and low-frequency signals are used in different ways, and the operating band advantages of the respective speakers are utilized as much as possible to ensure the speakers in different working frequency bands. Give full play to make the playback characteristics of each frequency more balanced.
2. Overcoming the cutting distortion caused by the vibration amplitude of the diaphragm of different frequency sound speakers
When the speaker is pronounced, its vibrating bass vibration amplitude is large and the high-pitched vibration amplitude is small. Theoretically speaking, the vibration amplitude of the speaker cone is inversely proportional to the square of the reproduction sound frequency, that is, the same speaker diaphragm, the lower the frequency, the larger the amplitude under the action of the signal voltage of the same amplitude, that is, if the frequency is increased 10 times, the amplitude will be reduced by a factor of 10, or 100 times.
If we use a single speaker to produce a wide range of frequencies, it is very difficult to have a very wide amplitude of vibration due to the mechanical properties of the diaphragm. This will inevitably cause distortion of the sound and make the sound quality reproducible. Affected.
The study found that the cutting distortion has the greatest influence on the bass. When the woofer delivers the bass, as long as there is a high-pitched component, it will inevitably lead to cutting distortion, causing the bass to tremble and tremble. Of course, the distortion of the tweeter will also make the treble hoarse, but it will not affect the bass.
3. Reduce sound interference between different speakers in the same speaker
For tweeters and subwoofers in high and low-range split speakers, although they work in different frequency bands, if the full-range signal is sent to the tweeter and woofer without dividing the frequency, high and low speakers will definitely appear. 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.
Anyone with a little common sense of acoustics knows that in the event of sound interference, there will be a series of problems such as comb filtering and standing waves, which will affect the sound reproduction to varying degrees.
After setting the frequency dividing circuit, the treble and woofer respectively obtain their own best working frequency sound signals, and the frequency range of sounds between them is hardly covered, except for a small amount of interference in the speaker crossover point and the crossover cross area. The interference of frequency sounds no longer exists.
The reason why the frequency interference phenomenon exists in the crossover point and the crossover crossover area is very simple, because the frequency division attenuation rate of the frequency divider cannot be made infinite, in the crossover intersection area, especially at the crossover point, the tweeter and the bass. The speaker will have the sound of the other band at the same time, and the phenomenon of sound interference is inevitable. Therefore, the higher the frequency division attenuation rate of the frequency divider, the smaller the frequency division intersection area, and the smaller the sound interference of the speaker.
Classification of frequency divider
There are two main types of frequency dividers: 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
The passive crossover is a built-in frequency divider for the speaker. It consists of a capacitor and an inductive filtering network. It is characterized by a crossover network placed between the power amplifier and the speaker. This crossover divides the full-range audio power signal directly from the power amplifier into bass and treble or bass, midrange and treble, and distributes the divided signals to the speakers of each band in different frequency bands. In the full-frequency high, low or high, medium and low-frequency active crossover speakers, the frequency division task is completed by the passive frequency dividing circuit.
The advantages of passive crossover are: firstly, the structure is simple, the cost is low, and it is installed with the sound, it needs to be adjusted and is easy to use. Secondly, it is easier to connect the system. Just input the full-frequency signal to the power amplifier and connect the amplifier to the speaker. Together, full-range playback can be achieved. Third, there is less power amplifier required. Generally, one power amplifier can carry two full-frequency passive crossover speakers, so the system cost is low.
The disadvantage of passive crossover is: First, the crossover network has to bear a lot of power and current applied to the speaker, so a larger volume of inductance is used, and since the inductance parameter has a direct relationship with the speaker impedance, 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 the inductive filter, it is bound to be nonlinear due to capacitance and inductance. Cause distortion, sound distortion is inevitable; Third, the audio power signal output from the power amplifier, each pass through a capacitor and inductor device will cause loss of power signal, so the passive frequency divider power signal loss is greater; Finally, the frequency divider attenuation The rate cannot be made too high, generally up to 12dB/octave, and the interference in the crossover crossover area is too large. This is because the way to improve the frequency division attenuation rate of the passive frequency divider is to increase the capacitor or inductor, that is, the filtering order. However, increasing the number of capacitors or inductors means increasing signal distortion and power loss, and increasing the frequency division attenuation rate. The result is a lot more problems.
As the name implies, passive frequency division is a kind of “frustrationâ€: the frequency division method, the full-frequency power signal output by the power amplifier has to be divided, and the frequency division will lead to a series of problems, so it can only be forced to divide the power signal. . In order to reduce system cost, civil speakers all adopt passive frequency division. Professional speakers are very different from those of civilian speakers in terms of requirements, listening subjects and users. In addition to passive crossover speakers, there are also active crossover speakers.
2. Active frequency divider
The active frequency divider is a device that divides the full-frequency audio weak signal, and is generally composed of an active electronic circuit frequency division system. The frequency division system is located in front of the power amplifier, and the full-frequency audio is weakly divided. The bass, treble or bass, midrange, and treble signals are sent to their respective power amplifiers, and then output by the power amplifier to the bass, treble or bass, midrange, and tweeters. This method is called active crossover. In the case of weak signals, the frequency division can be achieved with a low-power electronic active filter.
Each speaker unit of the passive crossover speaker has its own power signal interface. Some high- and low-bass discrete speakers can have active crossover and passive crossover. These speakers are equipped with active crossover. (Active) and passive crossover (Passive) switch, the switch on some speakers is also equipped with a locking mechanism to avoid false triggering. When adopting the active crossover mode, be sure to turn the crossover mode switch to the "Active" side, and connect the high-pitched power amplifier to the high-pitched (Hi2h) input and the bass power amplifier to the low-speed input.
The advantages of active frequency division are many. First, due to the use of weak signal electronic line 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 made higher than the passive frequency division. It is easy to reach 24dB/octave, the crossover crossover area is much smaller than the passive crossover, and the interference between the high and low volume sounds in the crossover crossover area is basically overcome; the third is good adjustability, electricity The sound index is high.
None of the shortcomings of active crossover is related to sound quality. The main problems are: First, high cost and large investment. Since the active crossover mode is high and the bass is used separately with separate power amplifiers, there are many power amplifiers, such as one-to-two distributed speakers to be driven by two amplifiers; the second is to add an electronic crossover, which makes Connection and adjustment aspects increase the difficulty of use.
As mentioned above, the frequency divider has two types: active frequency division and passive frequency division. The passive crossover is fixed inside the speaker and does not need to be adjusted by the sound engineer. The active crossover method has many problems such as the correct use of the electronic crossover, reasonable connection and adjustment, so this article only Several major issues that should be noted in the use of active crossovers are discussed.
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