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How to choose active or passive speakers

2021-08-19 415
1. Active VS Passive-Current Status
In any HIFI system, the speaker is a very critical component. It is not that other components are not important, but there is no doubt that the speaker can influence the sound quality of a HIFI system without considering the listening environment and sound source. The core of music playback.

In the history of loudspeaker development, from the "excitation type" and "constant magnetization type" in the 1930s to the "active" and "passive" today, there are great differences in the overall structure and frequency divider circuit. It can be said that it directly determines the tone of the speaker.

Active or passive, which system is better? Taking into account the factors mentioned before, it can be understood why so many Hifi enthusiasts mention this problem again and again. For decades, whether in magazines, newspapers, or even today's online forums, there have been various disputes to explain one's own views. The debate between active and passive is very controversial, and it is also a very important disagreement in the HIFI field.

But in fact, there may be many music lovers who still have a vague understanding of this controversy, and they cannot understand this issue correctly and clearly. So we also want to introduce you to the basic situation on this topic, such as the advantages and disadvantages of active and passive systems. We believe that both active and passive systems will coexist in the market. I hope to rationally analyze the differences between the two speakers from the fundamental differences in technology.

2. Active and passive-fundamental difference
Generally speaking, the difference between active and passive is determined by their power amplifiers and frequency dividers. The active system (defined strictly literally) is equipped with a built-in power amplifier and electronic crossover, while the passive system is driven by an external power amplifier, and the passive crossover is configured in the box . This means:

Passive speakers are connected to an external power amplifier, while active speakers have built-in power amplifier components.

This difference stems from the design of active speakers and passive speakers. The most influential factor is the connection sequence of the power amplifier and the crossover system. This brings out the second important point:

The design (structure) and components of the frequency division system.

Simply put: Active and passive speakers depend on whether they have built-in power amplifiers and the design of crossover circuits.

Active speakers, in addition to the built-in power amplifier, its frequency divider circuit contains electronic components (operational amplifier).

Passive speakers use an external power amplifier to drive the speakers, and the crossover circuit does not contain any electronic circuits.

3. Passive speaker system
The structure of the passive speaker, taking the three-way speaker as an example, the tweeter, midrange, woofer and three-way crossover are installed in the cabinet. Passive speakers need to use an external power amplifier to drive the speakers. Because passive speakers are power amplifiers that directly connect the signal to the frequency divider circuit for frequency division, and then drive the unit, and the frequency divider circuit does not contain any electronic circuits. Therefore, the power amplifier and the internal frequency divider of the speaker must have a perfect impedance matching before the speaker performance can be exerted. Among them, the "damping factor" of the power amplifier (DampingFactor) is an important indicator.

This coefficient refers to the accuracy with which the power amplifier controls the vibration of the paper tray (that is, the unit). A poor damping coefficient means that the power amplifier cannot control the vibration of the paper tray very well. The impact on the sound is unavoidable. Today, today, high-end power amplifiers can achieve very good damping coefficients. However, since the frequency divider of the passive speaker is located between the power amplifier and the unit, this will inevitably reduce the accuracy of the power amplifier control unit. Of course, the phase shift (PhraseShift) caused by components such as resistors, capacitors, and inductors in the frequency divider circuit also has a certain impact on the tone. Passive speakers must rely on an external power amplifier, and the signal input to the speakers will first pass through the (passive crossover) frequency division to connect the high/bass unit. The frequency divider will lose the input power of the power amplifier. The best (of course also very expensive) crossover system can reduce the loss of this process, but it can never be avoided.

Various coils, capacitors and other components are relatively large and conspicuous. It is obviously different from electronic crossover

4. Active speakers
The structure of active speakers, the power amplifier is installed in the box, and the frequency divider is an active electronic frequency divider circuit. After the signal source is connected to the speaker, it is first divided by the electronic frequency divider circuit, and then transmitted to the built-in power amplifier driving unit. Since it uses an active electronic frequency divider circuit, the parameters of the frequency divider can be processed more accurately. The new generation of active speakers use DSP technology, and the speaker functions can better meet the needs of users, such as adjustable frequency balance, input level, and memorize different settings to meet the needs of the listening environment. The power amplifier is built-in, and the connection line between the power amplifier and the unit is very short, and it can only be calculated with "inch" as the unit. The matching between the power amplifier and the unit has also been accurately calculated by the manufacturer. Users no longer need to worry about matching the speaker and the power amplifier. The term "damping factor" no longer exists. These are the unmatched advantages of passive speakers.

Take a three-way active speaker as an example to illustrate the signal transmission process

The original audio signal "≈" is sent directly (dotted line) to the electronic crossover system ● (thick dot) and separated into high, medium and low areas, respectively through the high pass (High Pass)

How to choose active or passive speakers

, Band Pass

With Low Pass

The filtering to form high, medium and low frequency signals. There is a dedicated power amplifier for each of the high, middle and low levels to amplify the divided signals. Finally, the amplified signals (thick lines) are sent to the respective units.

Click to enter the picture review

Active (electronic) frequency division system

Of course, the structure of the active speaker, the power supply, the power amplifier, and the electronic frequency divider circuit are installed in the box. There are still comments on the market that due to this structure, the active speaker has a poor "signal-to-noise ratio" index, and the active components in the cabinet interfere with each other. There is no denying that active circuits must generate thermal noise. However, electronic components continue to improve, and today thermal noise is negligible.

Other comments pointed out that the "instability" of active speakers is another issue that needs to be taken seriously. In the past, some active systems did have technical problems. Mainly because the design of the power amplifier is flawed, and there is a serious heating problem. Excessive heating is particularly easy to cause various problems, cause damage to the equipment, and reduce the service life.

However, this problem has been solved with the emergence of new power amplifier technology. ADAM's PWM (Pulse Width Modulation, Class D) power amplifiers have a very high working efficiency, up to 90%, which means that they only generate one-fifth of the heat equivalent to Class A/B power amplifiers. Thanks to the continuous development of various components and circuit technology, it is now possible to produce very good power amplifiers, which are veritable "top power amplifiers" in terms of technical parameters and actual sound quality.

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