Generally, cars are passive crossover systems (a few original cars have active crossovers, and some are semi-active crossovers). Passive crossover systems require frequency dividers, because most trebles cannot withstand excessive power. Burned. Therefore, the original car usually connects a small capacitor in series with the tweeter to perform the most basic frequency division.
The role of car dividerThe car audio kit speaker will be equipped with a frequency divider as standard. The main function is to decompose the output signal of the audio host or power amplifier into high-frequency, intermediate-frequency and low-frequency signals, and then output the sound to the speaker. This will make the speaker emit the frequency range that it allows to work, so that the human ear can hear the clearest and brightest sound.
Different crossovers in car audio
Active frequency division is that the audio signal of the host is divided in the host central processing unit before being amplified by the power amplifier circuit. The principle is that the audio signal is sent to the host central processing unit, and the audio signal in the host central processing unit is divided into low frequency according to the frequency response range Signal and high-frequency signal, and then input the two separated signals into the amplifying circuit, and amplify them separately.
Passive frequency division is that the audio signal is amplified by the power amplifier circuit and then divided by the passive frequency divider, and then input to the corresponding tweeter or woofer. The principle is that the inductance circuit filters out the high-frequency sound, leaving the low-frequency sound, and then The low-frequency sound is input to the low-pitched speaker. The low-frequency sound is filtered out by the electrolytic capacitor and the high-frequency sound is left, and then input to the tweeter.
Active frequency division is performed on the input end of the power amplifier. The load is the input end of the power amplifier. The impedance is high and stable, and it is not easy to cause frequency drift. The signal after the frequency division is amplified by the power amplifier and directly drives the speaker. With less non-linear distortion components, the distortion is reduced, and the intermediate insertion loss is reduced. The power transmission ratio is improved, and the transient state of the speaker without the insertion loss is also improved. The analytical power of the audio system is improved, and the details are more displayed. Clear, and for changes in the car environment, the crossover point can be adjusted according to the position of the horn to make the frequency connection smoother, and the sense of layering will be explained clearly. Each power amplifier working in a different frequency band can reduce intermodulation distortion and distortion. Different speaker signal transmission can use signal cables and speaker cables that are more suitable for a certain frequency band to make the signal transmission efficiency or sound characteristics more stylish.
However, since active frequency division requires the use of multiple power amplifiers, each speaker needs to be driven by an independent channel, which is costly and difficult to debug. Most car audio conversions still use passive frequency division.
Speakers and crossovers of car audio In professional audio, the tweeter unit is generally a horn-type speaker, while the woofer unit has a variety of forms such as direct type and airflow type. The reason for the sound interference phenomenon in the crossover point and crossover area is very simple. Because 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 also have the sound of the other party's frequency band, and sound interference is inevitable at this time. Therefore, the higher the crossover attenuation rate of the crossover is done, the smaller the crossover area of ​​the crossover, and the smaller the sound interference between the speakers.
The so-called high-bass separation speaker refers to a speaker in which the high-frequency part of the sound is played by a tweeter, and the low-frequency part is played by a woofer, rather than a speaker that completes the task of playing the entire audio frequency band. In professional speakers, the tweeter is generally a horn speaker, and the woofer has a variety of forms such as direct and airflow. Regardless of whether it is internal frequency division or external frequency division, high and bass separated speakers must adopt a frequency division sound reproduction scheme.
The principle of car dividerThe frequency division network of the loudspeaker is a circuit composed of L/C filters (inductance and capacitance). The design of the parallel frequency divider mainly adopts three basic filter forms. They are: low-pass filter, which attenuates the high frequency band, usually used in the bass unit; band-pass filter, which attenuates both the high-frequency and low-frequency ends, and is generally applied to the midrange unit; high-pass filter, which attenuates the low frequency range, Most of them are used in the tweeter.
The filter composed of L/C basically just uses the reaction characteristics of capacitance and inductance as a circuit for attenuating frequency. The characteristics of these components can be expressed by the formula of reactance (that is, the impedance of AC):
The above impedance formula illustrates the relationship between capacitance or inductance and frequency: the capacitive reactance of a capacitor is inversely proportional to the increase in frequency. When the frequency of the AC decreases, the capacitive reactance increases accordingly. The inductive reactance of an inductor is just the opposite of that of a capacitor. When the frequency increases, the inductive reactance also increases.
The filter can usually be described by three basic characteristics: the slope of the attenuation, the resonance and the Q value of the filter. The slope is generally in units of attenuation of each octave (octave), such as dB/Octave. When L and C are combined by different circuit forms, the slope of the filter can be opened to the attenuation of 6, 12, 18, 24dB per octave as shown in Figure 2-4-2. Crossover networks with attenuation of more than 24dB are rarely used. These attenuation rates can also be expressed by the order of the slope, the first order is 6dB/Octave, the second order is 12dB/Octave, the third order is 18dB/Octave, and the fourth order is the slope of 24dB/Octave.
When the order of the filter is greater than the first order, the circuit resonance frequency of the filter is when the reactance of the capacitor and the inductance are equal, that is, the frequency of the frequency division point. Therefore, the product of L and C is an important parameter, and different combinations of L and C values ​​can get different responses.
The Q value of the filter has the same relationship with the Q value of the unit, and the Q value after the unit is packed. The Q value is a parameter that describes the curve change at the crossover point. Different filter Q values ​​depict different attenuation response curves, as shown in Figure 6-4-3. Different response curves have different characteristics. They are all named after the engineer who first discovered these response characteristics. For example: Chebychev (Q = 1), Butterworth (Q = 0.707), Bessel (Q = 0.58), Linkwitz-Rily (Q = 0.49).
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