Horn Speaker unit and crossover technology introduction
Although different speakers may differ in the design of internal sound absorbing cotton, inverted tube, reinforcing disk/reinforced partition, etc., from the perspective of basic components, at least the following three parts must be present in any speaker. : Speaker unit (or speaker unit), cabinet and frequency divider.
The speaker unit of the speaker converts the electrical signal from the amplifier into a sound output, which plays the most important role in the electro-acoustic conversion of the speaker. The performance and sound quality of the speaker horn depend greatly on the performance of the speaker unit. Therefore, the prerequisite for manufacturing the speaker is to select the speaker unit with excellent performance.
The performance requirements of the speaker unit are summarized as follows: the bearing power is large, the distortion is low, the frequency response is wide, the transient response is good, and the sensitivity is high. However, it is necessary to take into account the distortion in the wide frequency range of 20Hz-20KHZ. The performance of transients, power, etc. is very difficult. Although the so-called all-rounders can get a certain balance on the whole, they are often mediocre in separate details. Therefore, the simplest idea in the speaker design is to make the speaker units Perform his duties and use sub-band playback.
For this reason, the PA Loudspeaker manufacturers produce different types of units, some are only responsible for playing the bass, called the woofer, the midrange unit for playing the midrange, and the tweeter is only responsible for playing the treble, so that the specific design can be adopted for each case. The performance of the unit is better.
Therefore, although it is theoretically possible to design a speaker using a full-band speaker, for the above considerations, the design of covering the entire audio band with a combination of multiple units accounts for the vast majority. The specific use of several units depends on the frequency division of the audio range. If it is simple to split the treble and the bass (or medium and low) two speakers is enough; if it is divided into three, three, three, three, three Speakers, then at least three units have to be used. Now the design of two low-frequency units working in parallel is also very popular, so the total number of units can reach four; some large speakers have a more detailed frequency band, if the unit is used again The design of the parallel operation will result in more total speaker units. In the speaker's data or manual, there is usually a "X-channel X unit" scheme, which is a specific description of the number of channels and the total number of units used, such as "three-way four-unit", indicating that this is a three-way design. The speakers used a total of four speaker units, and so on.
Dividers and Speaker Units Since most of today's speakers use a multi-cell sub-band playback design, there must be a device that can divide the full-band music signal from the amplifier into high-pitched, low-pitched or high-pitched sounds as needed. The midrange and bass output can be connected to the corresponding speaker unit. The crossover is such a device. If the full-band signal is directly sent to the high, medium, and low-range units without distribution, the portion of the "excess signal" outside the range of the unit's frequency response will adversely affect the signal reduction in the normal frequency band, and may even make The treble and midrange units are damaged.
From the circuit structure point of view, the frequency divider is essentially an LC filter network composed of a capacitor and an inductor coil. The treble channel is a high-pass filter, which only passes the high-frequency signal to block the low-frequency signal; the bass channel just wants to reverse it. Only the bass is passed to block the high-frequency signal; the mid-range channel is a band-pass filter, except that the frequency between the two low-high and high-frequency points can pass, and the high-frequency component and the low-frequency component will be blocked. In the actual crossover, sometimes in order to balance the sensitivity difference between the high and low woofer units, attenuating resistors are added; in addition, some frequency dividers also include an impedance compensation network composed of resistors and capacitors. Make the impedance curve of the speaker more flat to facilitate the amplifier drive. For a more detailed discussion of the speaker crossover method, refer to the article on the electronic crossover technology of PC multimedia speakers.
Types of Speaker Units There are many types of speaker units, and the classification methods are also different. If it is divided according to the principle of electro-acoustic conversion, there are types such as cone unit, flat unit, dome unit, belt unit, etc. Among them, the cone unit and the flat unit are more suitable for high pitch, and some middle units are dome type. Design; from the perspective of the covered frequency band, some midrange units also adopt a dome-type design; from the perspective of the covered frequency band, the speaker unit can be further divided into a woofer unit, a midrange unit, a tweeter unit and a full-band unit.
At present, the most common woofer and midrange units are electrically-type loudspeakers in principle. They use cone-shaped diaphragms because of the mature design and good performance of the diaphragm. There are many kinds of diaphragm materials, such as traditional paper diaphragms, diaphragms made of polymer synthetic materials (such as polyene), and diaphragms made of metal materials such as aluminum and magnesium. The requirements for the diaphragm are good rigidity (not easy to generate split vibration), light weight (good transient response), and proper internal damping characteristics (suppression of resonance), but these requirements are not easy to satisfy at the same time, but the rigidity is not strong enough; The rigidity of the diaphragm is very good, but the damping is not good. The polyene film has better performance in all aspects and has gained more applications in recent years. In addition, some manufacturers use a very complicated process to manufacture the diaphragm. The “sandwich” composite structure is one of them. The upper layer between the upper and lower surfaces sandwiches the middle layer of the honeycomb structure, and the whole has high rigidity, and at the same time It has the characteristics of light weight and good damping, and it has a promising future.
The most commonly used tweeter is the dome-type treble, which is also an electric unit from the working principle. The dome treble diaphragm can be made of metal material (such as aluminum, titanium, tantalum, etc.), called hard dome, or soft fabric (such as silk, chemical fiber), called soft dome, usually, hard sphere The top's high frequency response is better, while the soft dome's sound is softer. In recent years, belt treble and electrostatic treble have also been applied. Their common advantage is that the diaphragm is particularly light, so the high frequency response is excellent, the sound is slender and transparent, but the production of these two treble is as easy as the dome treble. Applications are less popular. There is also a horn treble, which is composed of a dome-shaped driving part and a horn-like horn. It is characterized by strong sound directivity and high efficiency, and is therefore widely used in professional loudspeakers. There is also a coaxial unit, which is actually a combination of bass and tweeter. For details, please refer to the relevant question and answer.
Installation requirements for the woofer and tweeter Generally speaking, the woofer must be boxed, and the treble can be loaded or not. There are two reasons why the woofer must be housed in a box: one to eliminate the "sound short circuit" phenomenon; the other is to suppress the low frequency resonance peak of the horn unit.
When the diaphragm of the woofer moves back and forth, in addition to the sound waves radiating forward, the phase of the sound radiation in both directions is exactly opposite, that is, 180 degrees out of phase. Since the wavelength of the low-frequency sound wave is very long, its diffraction ability is very strong, that is, the directivity of the low-frequency sound wave is very weak. If the speaker unit is not boxed, the sound wave of the backward radiation will wrap around to the front and the front. Radiation out of phase cancellation, the overall forward sound wave radiation energy is greatly weakened, this phenomenon is called "sound short circuit". The "sound short circuit" phenomenon must be managed to eliminate, otherwise the low frequency cannot be effectively radiated. If the speaker unit is placed in a box, the radiation behind the diaphragm is blocked by the box, and no "sound short circuit" is formed.
Each electric low-frequency unit has a low-frequency resonance point, and the output at this resonance point reaches a peak, but the distortion is also high, and the transient response is very poor. If this resonance peak is not suppressed, it will be seriously affected. The sound quality of the playback. If the unit is boxed, the stiffness of the air inside the box will inhibit the movement of the diaphragm, thus achieving the purpose of lowering the resonance peak and improving performance. In addition, by selecting the structure and parameters of the box, the purpose of widening the low frequency response can be achieved, and a well-designed inverter box, passive radiator speaker, and transmission line speaker can all achieve such an effect.
For the tweeter, the situation is completely different, because the high-pitched wave has a short wavelength, the diffraction ability is weak, there is no "sound short circuit" phenomenon, and it is not necessary to suppress the low-frequency resonance peak like the woofer. Therefore, for the tweeter, the speaker The role is just a support.
