Speaker unit and crossover technology introduction
Although different speakers may be different in the design of internal sound-absorbing cotton, inverted tubes, reinforced discs / reinforced partitions, etc., from the perspective of basic components, at least the following three parts are required in any speaker : Speaker unit (or speaker unit), cabinet and crossover.
Speaker unit of the speaker The speaker unit converts the electrical signal sent by the power amplifier into sound output, which plays the most critical role in the speaker-to-sound conversion. The performance index and sound quality performance of the speaker greatly depend on the performance of the speaker unit. Therefore, the prerequisite for manufacturing a good speaker is to select a speaker unit with excellent performance.
The performance requirements of the speaker unit are summarized in terms of high load power, low distortion, wide frequency response, good transient response, and high sensitivity, but it must also take into account the distortion in the full frequency range as wide as 20Hz-20KHZ , Transient, power and other performances are very difficult. Although the so-called all-around players can get a certain balance on the whole, they are often mediocre in individual details. Therefore, the simplest idea in the speaker design is to let the speaker unit each Do its duty and use sub-band replay.
To this end, speaker manufacturers produce different types of units, some of which are only responsible for playing bass, called the bass unit, the midrange unit is called the midrange unit, and the tweeter unit is only responsible for playing the treble. The performance of the unit is relatively good.
Therefore, although it is theoretically possible to design a speaker with a full-band speaker, for the above considerations, the design method of covering the entire audio frequency band with a combination of multiple units still accounts for the vast majority. The number of units used depends on the frequency division method of the audio range. If it is simply to divide the high-frequency and low-frequency (or low-mid) two speakers, it is enough; if it is a three-way frequency divided into high, medium and low three sections For speakers, you must use at least three units. Now the design method of two low frequency units working in parallel is also very popular, so that the total number of units may reach four; some large speakers are more finely divided. If you use units The design of working in parallel, the total number of speaker units will be more. In the speaker information or manual, there is usually a "X channel X unit" program, which is a specific description of the number of frequency division channels of the speaker and the total number of units used, such as "three channel four units", indicating that this is a three-way design The speakers used a total of four speaker units, and so on.
Frequency divider and speaker unit Since most current speakers adopt the design method of multi-unit sub-band playback, there must be a device that can divide the full-band music signal sent by the power amplifier into treble, bass output or treble, as needed. The midrange and bass output can only be connected to the corresponding speaker unit. The crossover is such a device. If the full-band signal is directly sent to the high, middle and bass units without distribution, the part of the "excess signal" outside the frequency response range of the unit will adversely affect the signal restoration in the normal frequency band, and may even cause The treble and midrange units are damaged.
From the circuit structure point of view, the crossover is essentially an LC filter network composed of capacitors and inductors. The treble channel is a high-pass filter, which only passes high-frequency signals and blocks this low-frequency signal; the bass channel just wants to reverse it. Only the bass passes to block this high-frequency signal; the midrange channel is a band-pass filter, except for the frequency between the two crossover points of one low and one high, both high-frequency components and low-frequency components will be blocked. In the actual frequency divider, in order to balance the sensitivity difference between the high and low units, attenuation resistors are also added; in addition, some frequency dividers also include an impedance compensation network composed of resistors and capacitors, the purpose of which is to Make the impedance curve of the speaker psychologically flat, so that the amplifier can be driven. For a more detailed discussion of speaker crossover methods, please refer to the article on electronic crossover technology for PC multimedia speakers.
Types of speaker units There are many types of speaker units, and the classification methods are also different. If divided according to the principle of electro-acoustic conversion, there are cone unit, flat unit, dome unit, belt unit and other types, of which cone unit and flat unit are more suitable for treble, and some midrange units adopt dome type Design; from the perspective of the covered frequency band, some midrange units also adopt dome-style design; from the perspective of the covered frequency band, the speaker unit can be divided into a bass unit, a midrange unit, a tweeter unit and a full-band unit.
At present, the most common bass unit and midrange unit belong to electric speakers from the principle of conversion. They mostly use cone-shaped diaphragms, because the shape of the diaphragm design is mature and the performance is good. There are many kinds of diaphragm materials, including traditional paper diaphragms, diaphragms made of polymer synthetic materials (such as polydiene), and diaphragms made of metal materials such as aluminum and magnesium. The requirements for the diaphragm are good rigidity (not easy to produce split vibration), light weight (good transient response), and appropriate internal damping characteristics (resonance suppression), but these requirements are not easy to meet at the same time, but the rigidity is not strong enough; metal The rigidity of the diaphragm is very good, but the damping is not good; the polydiene diaphragm takes good care of 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 middle layer of the honeycomb structure is sandwiched between its upper and lower surfaces, which has a high rigidity as a whole. It has the characteristics of light weight and good damping, which is very promising.
The tweeter is the most commonly used dome tweeter, which also belongs to the electric unit in terms of working principle. The dome tweeter's diaphragm can be made of metal materials (such as aluminum, titanium, beryllium, etc.), called hard dome, or can be made of soft fabric (such as silk, chemical fiber), called soft dome, usually hard ball The high frequency response of the dome is better, while the soft dome sound is softer. In recent years, band tweeters and electrostatic tweeters have also been used to some extent. Their common advantage is that the diaphragm is particularly light, so the high frequency response is excellent, and the sound is delicate and transparent. However, the production of these two tweeters is as easy as dome tweeters. The application is not very popular. There is also a horn treble, which is composed of a dome-shaped driving part plus a trumpet-shaped horn. It is characterized by strong sound directivity and high efficiency, so it is widely used in speakers in the field of professional sound reinforcement. There is also a coaxial unit, which is actually a combination of bass and treble units. For specific characteristics, please refer to the relevant question and answer.
Installation requirements of woofer and tweeter Generally speaking, the woofer must be boxed, but the treble can be installed or not. There are two reasons why the bass unit must be packed in a box: one is to eliminate the "acoustic short circuit" phenomenon; the other is to suppress the low-frequency resonance peak of the speaker unit.
When the diaphragm of the woofer moves back and forth, in addition to the sound waves radiating forward, the phases of the sound radiation in the two directions are exactly opposite, that is, they are 180 degrees apart. Because the wavelength of low-frequency sound waves is very long, its diffraction ability is very strong, that is to say, the directionality of low-frequency sound waves is very weak. If the speaker unit is not boxed, the backward radiated sound waves will go to the front and the front The radiation cancels out of phase, and the overall forward sonic radiation energy is greatly weakened. This phenomenon is called "acoustic short circuit". The "acoustic short circuit" phenomenon must be eliminated, otherwise low frequencies cannot be radiated effectively. If the speaker unit is installed in the box, the radiation behind the diaphragm is blocked by the box, so there will be no "acoustic short circuit".
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 very high, and the transient response is very poor. If this resonance peak is not suppressed, it will inevitably be seriously affected The sound quality of the playback. If the unit is boxed, the stiffness of the air in the box will inhibit the movement of the diaphragm, thus achieving the purpose of suppressing the resonance peak and improving performance. In addition, by rationally selecting the structure and parameters of the cabinet, the purpose of broadening the low-frequency response can be achieved. A well-designed inverter box, passive radiator speaker, and transmission line speaker can achieve this effect.
For the tweeter, the situation is completely different, because the tweeter has a short wavelength and weak diffraction ability, there is no "acoustic short circuit" phenomenon, nor does it need to suppress low-frequency resonance peaks like the woofer, The effect is just a support.
- 5 Way Power Strip with overload protection can protects your electrical devices from over current damage. Energy Saving Power Board can be combined with USB Port, Surge Protector, Overload Protector, Double Break Switch or Individual Switches and so on.
- 5-Outlet Electric Socket Extension can be hang on the wall or mounted on desk or so.
- PC+ABS flame retardant, phosphor bronze+pure copper. Compliance with international standards.
5 Way Power Strip
5 Way Power Strip, Energy Saving Power Board, Power Strip Individual ON OFF Switches, 5-Outlet Electric Socket Extension, Electrical Outlet USB
ZhongShan JITONGLONG Plastic Hardware Co. Ltd. , https://www.toukoo-electronics.com