When dismantling a speaker, apart from the tuning materials used by manufacturers, one will also find a circuit board sandwiched between the output terminal and the sound-producing unit. This circuit board is known as the crossover, which functions as the "brain" of the speaker. It divides analog signals into different parts such as high, mid, and low frequencies, sending them to their corresponding sound-producing units to achieve better playback quality.

The crossover is commonly used in speakers with high and low-frequency units, or those equipped with mid-frequency units. Without the crossover, such multi-unit speakers would be unable to replay sounds across different frequency ranges. Moreover, the type and quality of the crossover significantly impact the speaker's ability to produce superior sound quality.

Why is the crossover essential? Both high and low-frequency speakers have uneven frequency response curves, with attenuation at both ends. Sometimes, the attenuation of the upper limit of the low-frequency response may overlap or intersect with the attenuation of the lower limit of the high-frequency response, resulting in frequency band overlap and an inability to form a flat curve. This would undoubtedly lead to substandard sound quality.

Simply connecting the speakers together does not ensure their harmonious operation. The crossover plays a crucial role in orchestrating the frequency response of various speakers to achieve better results. It processes the music signals output by the power amplifier through filtering components, allowing specific frequency signals to pass through each unit. In essence, the crossover splits the original signal into several frequency bands, selects the most suitable band for each corresponding unit, and distributes it accordingly, enabling multiple speakers to work together synergistically.

The need for a crossover is determined by the design of the speaker itself. A two-way crossover divides the signal into two segments, while a three-way crossover divides it into three. These are commonly referred to as "two-channel" and "three-channel" configurations. Depending on its working principle, the crossover can be categorized into different types of designs. However, the two most commonly encountered types are the power crossover and the electronic crossover.

The power crossover, centered on electronic components, is designed to operate after the power amplifier. Primarily composed of capacitors and inductors, it is also known as an inductive-capacitive crossover. The filtering effects of inductors and capacitors enable low-pass and high-pass filtering, ultimately achieving frequency division. This type of crossover is installed inside the speaker and uses an LC filter network to divide the audio signal output by the power amplifier into high, mid, and low frequencies, which are then sent to each sound-producing unit.

The simplest form of power crossover is capacitive crossover, which involves connecting a capacitor in series with the high-frequency unit to achieve frequency division. More complex designs may employ capacitors and inductors in each channel to achieve more precise frequency division. Regardless, the installation of a power crossover is relatively straightforward, compatible with both active and passive speakers. However, it exhibits attenuation in the frequency bands after division, with the slope of the attenuation curve typically related to the order of filtering.

Despite its usefulness, the power crossover has some notable drawbacks. It consumes power, which can lead to audio valleys and cross-distortion. Furthermore, the parameters of the power crossover are closely related to the impedance of the speaker unit, which can vary significantly from its nominal value due to being a function of frequency. This introduces significant errors, making tuning challenging and often requiring extensive experience and expertise to achieve optimal results.

On the other hand, the electronic crossover operates before the power amplifier. It divides the weak audio signal into different frequencies, which are then amplified by independent amplifiers and sent to the speaker units for playback. For example, in a two-way speaker using an electronic crossover, a two-channel signal would be split into four, necessitating a four-channel power amplifier for complete output.

The electronic crossover offers several technical advantages. Unlike the power crossover, it does not consume significant power. With a smaller current, it can be implemented using a low-power electronic active filter, making its power loss negligible. Additionally, the interference between speaker units is reduced, resulting in less signal loss and slightly improved sound quality. Moreover, tuning is more intuitive and convenient with an electronic crossover.

However, the electronic crossover also has its limitations. Due to its operating principle, each channel requires a separate power amplifier, increasing costs and complexity in circuit design. Nevertheless, compared to the higher cost of materials like brass in power crossovers, the electronic crossover may still offer cost advantages. Additionally, since the electronic crossover is typically integrated with the power amplifier system, it may not offer the same level of customization and tinkering opportunities for DIY speaker enthusiasts.