Analysis of electronic frequency division technology of multimedia speakers

However, recently many multimedia speakers have emerged on the market that claim to use electronic crossover technology. So, how should we view these "electronic crossover" technologies: are they publicity gimmicks or real technological advancements?

The concept and significance of frequency division
As we all know, the human ear's perception range of sound frequency is approximately between 20Hz and 20KHz, and the frequency span is very large. However, due to the limitations of principles and technology, the current mainstream speakers cannot use one unit to perfectly reproduce all the frequency bands that the human ear can hear. Therefore, tweeters and woofers for different frequencies appear.

The frequency range of the woofer used in current multimedia speakers is approximately 40Hz - 4KHz, and the frequency range of the tweeter is approximately 2KHz - 20KHz. That is, at least two units are required to cover all the frequencies that the human ear can hear. The crossover is the bridge that connects the tweeter and the woofer so that they can work synchronously and harmoniously.

On the other hand, since the tweeter can withstand a small amount of power, if a large power is input or it is allowed to work in a low frequency band, it is very easy to cause the tweeter to be damaged or even burn out. Therefore, a crossover is also needed to divide the frequency so that the tweeter can work within a safe frequency range.

Power frequency division: the frequency division method of traditional PC multimedia speakers
The so-called power frequency division means that the sound signal is first amplified, and then the treble and bass signals are separated through the frequency division circuit composed of high-pass, low-pass, band-pass and other passive filters, and sent to the corresponding treble and bass units respectively. The power frequency divider circuit is simple and can be realized by using a standard LC circuit, namely an inductor (L) and a capacitor (C). As shown below:

The advantages of power dividers are that they are relatively simple in structure, low in cost, and easy to produce and manufacture. For PC multimedia speakers, only one power amplifier is needed for each channel, which can greatly reduce production and manufacturing costs. Therefore, they are widely used. Currently, almost all active speakers use power dividers.

The disadvantage of power dividers is that inductor coils are often large in size and have DC resistance, which results in a large insertion loss and reduces the damping coefficient. - The so-called damping coefficient reflects the control of the power amplifier over the speaker, and its value is speaker impedance/(power amplifier internal resistance + transmission impedance). Generally speaking, the internal resistance of the power amplifier is generally 0.1 ohms, while the internal resistance of most power dividers exceeds the internal resistance of the power amplifier and even reaches more than 0.2 ohms, which means that the power divider reduces the damping coefficient by half or more. - Therefore, the power divider has a great negative impact on the control.

At present, almost all PC multimedia speakers use integrated amplifiers, which have very limited thrust and control. The insertion loss of the power divider and its influence on the damping coefficient further aggravate the defects of the integrated amplifier in thrust and control, making the bass muddy and blurred, and losing the necessary details. For example, we can often clearly feel that the bass of some PC multimedia speakers is slow and the sound is not clear. In fact, this is the insertion loss of the power divider.

Principle of electronic crossover
Electronic crossover is sometimes also called active crossover. The biggest difference between it and power crossover is that electronic crossover is to divide the audio signal through the electronic crossover circuit before it is sent to the power amplifier, and then send the signals of different frequency bands after the division to their respective power amplifiers to drive the speaker units of different frequency bands.

It can be seen that the advantages of electronic crossover are, first of all, because the power amplifier directly drives the speaker, there is no insertion loss caused by the power crossover and the influence on the damping coefficient. Therefore, electronic crossover can significantly improve the control of the power amplifier, increase the analysis power of the whole frequency band, make the speaker flexible, the sound is clear and powerful, and the sense of speed is strong; secondly, the accuracy of electronic crossover is easy to control, and the use of high-quality devices can accurately control the crossover point, so that the high and low frequency units can work in the most appropriate frequency band respectively, so as to give full play to the performance of the speaker, which is difficult to achieve with power crossover.

The main disadvantage of electronic crossover is the high cost, because each channel needs to be equipped with a corresponding power amplifier circuit, which requires the number of amplifiers to be increased exponentially.

Implementation mechanism of electronic frequency division
Let's take a closer look at how electronic frequency division is currently implemented in PC multimedia speakers and how the divided signal is amplified. The following is an electronic frequency division amplifier of a 2.0 speaker. Generally speaking, due to the use of electronic frequency division, the number of amplifiers for 2.0 speakers needs to be doubled, that is, 4-channel amplifiers are required, and the cost is higher than that of ordinary 2.0 speakers.

Due to the different characteristics and requirements of the tweeter and woofer, the speaker uses an 1875+7265 amplifier combination.

The treble channel uses the 1875 amplifier chip. Since multimedia sound sources generally have "digital sounds" and sound rough, the 1875 has a full and mellow tone, soft and delicate high frequencies, and can neutralize the rough digital sounds of multimedia sound sources, so it is very suitable for use in the treble channel.

The bass channel uses the original ST TDA7265 chip. TDA7265 has high power, strong thrust, and good control. When combined with electronic frequency division, it can fully exert its strong control.

From the actual effect, the combination of 1875+7265 is acceptable, which brings out the respective advantages of the two chips, ensuring sufficient sound quality and naturally revealing musicality during playback.

Rationally look at electronic frequency division
From the above introduction, it can be seen that the introduction of electronic frequency division technology in PC multimedia speakers should, in theory, be able to improve the sound quality to a certain extent and give full play to the potential of the speakers.

However, speakers are products that require human ears to feel subjectively. No matter how beautiful its frequency curve is, it is not enough. In many cases, it is not necessarily that good performance can be achieved by adjusting the frequency curve flat and straight. The theoretical advantages of electronic frequency division technology require the design and quality of other components as a guarantee. In many cases, the effect of electronic frequency division depends on whether the frequency division point is set reasonably, and even more on the quality of components. For the components in the above examples, it is difficult to say that the circuit and materials are rigorous. Of course, this is also a helpless choice to ensure that the cost of the speaker is within a certain range. But this also shows that the use of electronic frequency division technology alone does not mean that a certain speaker will necessarily have better sound quality than a speaker using power frequency division.