The difference between active and passive car audio is simply to distinguish between frequency division processing before and after power amplification. The frequency division is called active before the power amplification, and the frequency division processing at the output of the power amplifier is called passive frequency division. . Both active and passive have their own advantages. Voices also have their own advantages and disadvantages. They need to make choices according to their own needs, rather than taking the initiative to play when others are willing to take the initiative. Here are the advantages and disadvantages of these two types of frequency division.
This paper first introduces the classification of frequency dividers and the working principle of electronic frequency dividers. Secondly, the advantages and disadvantages of active frequency dividers are introduced. Finally, the advantages and disadvantages of passive frequency dividers are introduced.
There are two types of frequency dividers: PassiVe Crossover (also known as power divider) and Active Crossover (also known as electronic crossover).
How active divider works (electronic crossover)The electronic frequency divider uses various types of active filters (high-pass, low-pass, and bandpass) 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 follower component consists of an attenuation characteristic that increases with the increase of the RC order (by increasing the first order, the attenuation slope increases by -6db/out).
The electronic frequency division method has only a power transmission line between the power amplifier and the speaker. There is no other link that affects the sound quality, which reduces distortion and improves the damping factor of the power amplifier to the speaker. Because the load of the electronic divider is the input of the power amplifier, the impedance is high and stable, so the crossover point can be easily adjusted. And controlling the frequency division accuracy, and because the bandwidth of each frequency band of the electronic frequency divider is narrow, the higher harmonic waves caused by nonlinear distortion are suppressed, and the total harmonic distortion and the intermodulation distortion are reduced, and the electronic frequency divider overcomes There are disadvantages in the power divider, but it increases the cost and the difficulty of system debugging, so it is mostly used in professional situations.
1ã€Schematic diagram of two-way frequency divider
Figure 7-32 shows a block diagram of a divide-by-two electronic 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 of the corresponding frequency band, and then invert this signal. The full-screen input signal is summed to obtain another frequency band signal.
2. The working principle of the three-way frequency divider
The divide-by-three circuit uses a filter operation synthesis method. On the basis of the divide-by-two circuit, as long as the signals output by the high-pass and low-pass filters are all inverted and added to the full-band signals, an 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-range signals into high-pass, band-pass, and low-pass filters, respectively, to obtain corresponding high, medium, and low-frequency signals.
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 characteristic is that 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, high pitch signals are sent to their respective power amplifiers, and then output by the power amplifier to the bass, treble or bass, midrange, tweeter, this method is called active frequency division, because the work In the case of weak signals, it is possible to use a low-power electronic active filter to achieve frequency division.
Each speaker unit of the passive crossover speaker is equipped with its own power signal interface. Some high- and bass-resolved speakers can have both active and passive crossover connections. Active rearranging is provided behind the speakers. (Active) and passive (Passive) switch, some switches on the speaker switch is also equipped with a locking mechanism to prevent accidental toggle situation. When adopting the active frequency division method, be sure to switch the crossover mode switch to the “Active†side and connect the high-range amplifier to the Hi2h input and the bass amplifier to the Low input.
1, the advantages of active frequency division
The first is the use of weak signal electronic circuit signal for frequency processing, so the sound signal loss is small, distortion is small, reproduction sound quality is good; Second, the frequency attenuation rate can be higher than the passive frequency, to 24dB / octave very It is easy to divide the crossover area to be much smaller than the passive crossover, and the interference between the high and bass unit sounds in the crossover area is basically overcome. Third, the adjustability is good and the electroacoustic index is high.
2, the disadvantage of active frequency division
No one is related to sound quality. Its main problems are: First, high costs and large investments. Because the active frequency division method is high and each bass uses an independent power amplifier, each uses more power amplifiers. For example, one to two distribution loudspeakers need to be driven by two power amplifiers; the second is to add an electronic frequency divider, which makes Connections and adjustments increase the difficulty of use.
Passive frequency divider is a built-in frequency divider of the speaker, which is composed of capacitance and inductance filter network. Its characteristic is that the frequency division network is set between the power amplifier and the speaker. This divider 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 signal to the speakers of each frequency band in different frequency bands. In the full-range high, bass or high, medium and low frequency active frequency division loudspeakers, the frequency dividing task is completed by the passive frequency dividing circuit.
1, the advantages of passive frequency division
First of all, the structure is simple, the cost is low, and it is installed together with the sound, it needs to be adjusted, and it is convenient to use. Secondly, it is relatively easy to connect the system. As long as the power amplifier inputs the full-range signal, the amplifier and the speaker can be connected together to achieve full frequency. Third, less power amplifiers are needed. Generally, one amplifier can have two full-frequency passive crossover speakers, so the system cost is lower.
2, the disadvantages of passive frequency division
First of all, the crossover network has to bear a large amount of power and current applied to the speaker, so a larger volume of the inductor is used, and because the parameters of the inductor are directly related to the speaker impedance, the impedance of the speaker is a function of the frequency. The deviation of the nominal value is large, 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 will inevitably be distorted due to the non-linearity of the capacitance and inductance, and the sound distortion will be unavoidable. Thirdly, the audio power signal output from the power amplifier will pass through each time. Capacitance and inductance devices will cause the loss of power signal, so the power loss of passive frequency division is large;
Finally, the frequency division attenuation rate cannot be made too high. Generally, the maximum frequency is 12dB/octave. The interference in the frequency division crossover area is too large. This is because the passive frequency 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 that the signal distortion and power loss are increased, and the result of increasing the frequency division attenuation rate brings about other problems.
As the name suggests, passive frequency division is a kind of "frustration" of the frequency division, power amplifier output full-range power signal must be divided, undivided frequency will lead to a series of problems, it can only be forced to divide the power signal processing. In order to reduce system costs, civilian speakers all use passive frequency division. Professional speakers are different from the civilian speakers in terms of requirements, listening to the main body and the use of personnel, so in addition to passive crossover mode speakers, there are active crossover mode speakers.
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