The speaker is also known as the speaker system. It assembles high, medium and woofer speakers in a specially designed cabinet, and sends the high, medium and low frequency signals to the corresponding speakers through a crossover network for playback. After the loudspeaker is installed in the loudspeaker, the propagation characteristics of the sound inside the loudspeaker can be used to expand the low-frequency reproduction range of the loudspeaker, so that the reproduced sound can produce a larger sound field.
Speakers are classified according to the frequency division method: single speaker speakers; two-way speakers; three-way speakers; four-way speakers; multi-frequency speakers; subwoofer speakers (subwoofers). According to the classification of use, there are mainly: floor-standing speakers; bookshelf speakers; active speakers; surround speakers; monitor speakers; speakers for theaters and theaters; speakers for stage and so on. Speakers are classified according to their internal structure: closed, inverted, labyrinth, front horn, empty paper cone, symmetrical drive, Kelton, dumbbell, etc. The following mainly introduces closed speakers and inverted speakers.
1. Airtight speaker
There are many types of enclosed speakers in the market. For example, the AR series speakers in the United States are the most representative one. The enclosed speakers with a very low speaker unit fo are often called "air-cushioned" speakers in foreign countries. Small enclosed speakers The main adaption conditions of the horn are: should choose the horn monomer with small diaphragm diameter, low resonant frequency and great compliance.
Closed speakers are one of the most used speakers at present. The so-called closed sound box is to install the speaker in a completely enclosed box. It uses the box to separate the sound radiation from the front and back of the speaker to prevent acoustic short circuit. The air in a closed speaker is like a spring to the speaker, which improves the low-frequency response of the speaker.
The replay characteristics of the enclosed speakers are deep bass and better bass resolution. However, because the air in the closed box also has a certain damping effect on the motion of the speaker, it has a certain impact on the resonance frequency f 0 of the speaker and the quality factor Qt. If the box is larger, this effect is still small, but in In actual use, the main focus is on selecting the f0 and Qt of the speaker. In addition, since the enclosed speaker only uses the sound radiation from one side of the speaker, the efficiency is low, generally 3~5dB lower than other types of speakers.
In order to maximize the effect of air-cushioning of small airtight speakers, the thickness of the speaker diaphragm is often increased a lot. Under this condition, the efficiency of the speaker will be relatively lower, and the output will also be reduced, so it is compared with most inverted-type speakers. The speakers are more difficult to push, this is where the closed speakers are insufficient. But the advantage of closed speakers is that they are simple to produce, which is convenient for mass production and amateur production by enthusiasts. From the perspective of high fidelity, compared with other types of speakers, closed speakers have the lowest distortion, fast speed, accurate and deep bass, good control, and the phase characteristics are unmatched by other types of speakers. To describe it in feverish language: the low frequency reproduced by a closed speaker is a true bass effect, while a reflective speaker needs to use a suitable inverted phase on the cabinet because of the use of the body sound behind the speaker unit. In this way, the sound radiation wave has to undergo a 180-degree phase inversion in the speaker, and then radiate from the phase inversion hole to increase the radiation energy of the sound. On the surface, the efficiency is improved, but due to the need for sound waves After a period of time in the box, it can be released from the inverted hole and added to the front sound wave. There is a time delay problem. Strictly speaking, the reflected sound wave is compared with the front sound wave in time. There is a difference. Of course, the sequence of reaching the ears is also different, and the phase is also different, so it is a kind of false bass reproduction. However, because the human ear’s low frequency response is far less sensitive than the mid-to-high frequency, the phase-inverted speaker These gaps will not have much impact on the sense of hearing and the mind. Because of the high efficiency of reflection, they are still loved by people and occupy a huge proportion in the market.
2. Inverted speaker
Inverted speakers, also known as low-frequency reflective speakers, are currently widely used speakers. The theory of inverted speakers was proposed by ALThuras as early as 1932. In 1952, BNLocanthi proposed the calculation method of the interaction between the diaphragm and the gas of the inverted hole, which promoted the development of inverted speakers. In 1961, ANTniele used Novak to determine the simplified model that gave the inverted speaker a mature and practical design. It published many practical design methods in detail, and later RHSmall also designed the full method of inverted speakers. Publish more practical and meaningful articles. In the course of decades of development, phase-inverted speakers have gradually matured.
The difference between it and a closed speaker is that an inverter tube is installed on the panel of the speaker. When the speaker is working, the sound waves radiated from the back pass through the inverter tube and radiate to the front, superimposed with the sound wave in front of the speaker, and then work together. Radiate forward to enhance the low-frequency effect.
The characteristic of the inverted speaker is that it can use the resonance of the cabinet and the inverter to expand the low frequency when the sound pressure of the speaker remains unchanged, and its low frequency can be expanded to 0.7 times the resonance frequency of the speaker. Compared with a closed speaker that reproduces the same frequency, an inverted speaker is 70% smaller in volume than a closed speaker, so the output power requirement of the power amplifier is lower than that of a closed speaker. The inverter tube can reduce the amplitude distortion of the speaker near the lower limit frequency of the low frequency, but the transient characteristics of the inverter speaker are worse than the closed speaker. )
A well-designed inverted speaker can further expand the lower limit frequency of low-frequency balanced playback without reducing the sound volume. We know that the speaker unit has a basic resonance point frequency. At this frequency, the output sound will be the largest, and the distortion will also be the largest. If it is not controlled, it will inevitably cause the unevenness of the low frequency band of the sound box to increase. , The balance deteriorates and the distortion increases sharply. A reasonably made inverted speaker should be able to lower the basic resonance peak of the speaker, making it into two small peaks separated from the left and right, and the two small peaks are equal in size, so that the small peak that extends to the low end will also make the speaker The frequency response is further extended to low. Obviously, after the basic vibration peak pressure is lowered, the distortion is also significantly reduced. This is because the horn's vibration at this point is in a [sensitive term] state of fine vibration, and near this frequency, the amplitude of the vibration becomes smaller.
In order to take advantage of these advantages of the phase-inverted speaker, the designer must clearly understand the meticulous design chosen to get the ideal replay effect. It is not just a chance to open a phase-inverted hole to succeed. Inverted speakers also have strict requirements on the Qo of the unit. Without a specific Qo value, the advantages of inverted speakers cannot be fully utilized, and the adjustment procedures are also more complicated.
Although the inverted speaker has the advantages of high efficiency, good low frequency characteristics and small size, it also has disadvantages. The main reason is that it is difficult to design and make adjustments. For example, the inverter hole cannot be opened too large just for efficiency, otherwise it will form a peak. At the same time, the length of the inverter hole will have a greater impact on the low frequency, and poor design will easily produce bass. Problems that are too heavy or slow, and there may also be problems such as too loud airflow. Compared with closed speakers, the transient characteristics of the inverted speakers in the low frequency range are poor, and the sound performance is a bit muddy. Because the inverted speakers use the sound waves on the back of the speakers to be reflected in the cabinet for a period of time, so the phase It is not very accurate. At the same time, the reflected sound wave must be a step slower than the direct sound from the front of the speaker. Therefore, the inverter box emits a kind of "false" low frequency, which is not as accurate as a closed speaker.
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