1. Speaker


There are many types of speakers: according to their energy conversion methods, they can be divided into electric, electromagnetic, piezoelectric, digital, etc .; according to the structure of the diaphragm, they can be divided into single paper cone, composite paper cone, composite horn, and A variety of shafts; according to the beginning of the diaphragm, it can be divided into cone type, dome type, flat plate type, belt type, etc .; according to the playback frequency, it can be divided into high frequency, intermediate frequency, low frequency and full band speakers; according to the magnetic circuit The form can be divided into external magnetic type, internal magnetic type, double magnetic circuit type and shielding type; according to the magnetic circuit nature, it can be divided into ferrite magnet, neodymium boron magnet, aluminum nickel cobalt magnet speaker; Separate paper and non-paper cone speakers.

A. The dynamic speaker is the most widely used. It uses the interaction force between the voice coil and the constant magnetic field to make the diaphragm vibrate and sound. Most of the electric woofers are cone type, the mid-range speakers are mostly cone type or dome type, and the tweeters are usually dome type, belt type and horn type.

B. The cone type speaker has a simple structure and high energy conversion efficiency. The diaphragm material it uses is mainly pulp material, or blended with wool, silk, carbon fiber and other materials to increase its rigidity, internal damping and waterproof performance. The new generation of electric cone speakers use non-paper diaphragm materials, such as polypropylene, mica carbide polypropylene, carbon fiber textile, bulletproof cloth, hard aluminum foil, CD corrugation, glass fiber and other composite materials, performance improvement has improved.

C. The dome speakers are divided into soft domes and hard domes. Vibrating diaphragm silk, silk, cotton cloth impregnated with phenolic resin, chemical fiber and composite materials of soft-ball loudspeakers are characterized by soft and reproducible sound quality. Its characteristic is that the replay sound quality is crisp.

D. The radiating method of the horn type speaker is different from the cone type speaker. This is after the diaphragm vibrates, the sound diffuses out through the horn. It is characterized by high electro-acoustic conversion and radiation efficiency, long distance and low distortion, but the playback frequency band and directivity are narrow.

E. The voice coil of the band speaker is directly made on the whole diaphragm (aluminum alloy polyimide film, etc.), and the voice coil is directly coupled with the diaphragm. The alternating magnetic field produced by the voice coil interacts with the constant magnetic field, causing the belt diaphragm to vibrate to radiate sound waves. It is characterized by fast response speed, low distortion, fine playback sound quality and good sense of layering.

2. Cabinet

The cabinet is used to eliminate the acoustic short circuit of the speaker unit, suppress its acoustic resonance, widen its frequency response range, and reduce distortion. The box structure of the speaker is divided into bookshelf type and floor type, as well as vertical type and horizontal type. The internal structure of the box has closed, inverted, belt type, empty paper cone, labyrinth, symmetrical drive and horn type. The most used are closed type, inverted type and belt type .

Floor-standing speakers are large speakers, the height of the cabinet is above 750MM, the height of the bookshelf speakers is below 750MM, those between 450MM and 750MM are medium-sized bookshelf speakers, and those below 450MM are small bookshelf speakers.

The front main speakers of the home theater system are upright speakers, some of which use bookshelves, and some use floor-standing, which depends on the size of the listening room, the power of the power amplifier, and personal preference. Generally, medium-sized bookshelf speakers should be used for audiovisual rooms below 15 square meters; small bookshelf boxes should be used for those less than 10 square meters; medium-sized bookshelf speakers or floor boxes can be used for rooms larger than 15 square meters. The front main speakers, center speakers and surround speakers are mostly in inverted phase design, followed by closed work and 1/4 wavelength loading type, labyrinth type and so on. Subwoofer speakers are mostly of the band type and double-cavity double-opening type, followed by the inverted type and closed type.

3. Frequency divider

The frequency divider has the power frequency divider and the electronic frequency divider, the main functions are frequency band division, amplitude frequency characteristic and phase frequency characteristic correction, impedance compensation and attenuation.

The power divider, also called passive post-stage divider, divides the frequency after the power amplifier. It mainly consists of passive components such as inductance, resistance and capacitance to form a filter network, and sends the audio signals of each frequency band to the speakers of the corresponding frequency band to replay. Its characteristics are low production cost, simple structure, suitable for amateur production, but large insertion loss, low efficiency, and poor transient characteristics.

Electronic crossover is also called active front-end crossover. It is composed of various resistance-capacitance components and active devices such as transistors or integrated circuits. It is an analog placed in the signal lines of preamplifiers and power amplifiers. The electronic filter can divide the audio signal output by the preamplifier into different frequency bands, and then send it to the power amplifier for amplification processing. Its characteristic is that the frequency spectrum of each frequency band is balanced, the mutual interference is small, the output dynamic range is large, it has a certain amplification capacity, and the insertion loss is small. But the circuit configuration is relatively complicated.

The frequency divider can be divided into two frequency division, three frequency division and four frequency division according to the frequency division frequency band. Two-way frequency is to divide the entire frequency band of the audio signal into two frequency bands of high frequency and low frequency; three-way frequency is to divide the entire frequency band into three frequency bands of high frequency, intermediate frequency and low frequency; Ultra-low frequency band.

The crossover point and crossover slope directly affect the crossover quality (crossover frequency).
Crossover point refers to the intersection of the frequency response curves of two adjacent speakers (such as treble and bass in the second frequency division, treble and midrange in the third frequency division, midrange and bass) at a certain frequency, usually The frequency at the half of the power output of the two speakers (ie -3dB point) should be determined according to the frequency characteristics and distortion of the speaker and each speaker. Usually, the frequency dividing point of the two-way frequency divider is between 1KHZ ~ 3KHZ, and the three-way frequency point is two frequency points of 250HZ ~ 1KHZ and 5KHZ.
The crossover slope (also called the attenuation slope of the filter) is used to reflect the falling slope of the frequency response curve below the crossover point, expressed in decibels / octave (dB / oct). It is divided into first order (6 dB / oct), second order (12 dB / oct), third order (18 dB / oct) and fourth order (24 dB / oct), the higher the order, the frequency after the crossover point The greater the slope of the curve. The more commonly used is the second-order crossover slope. High-order frequency dividers can increase the slope, but the phase shift is large; low-order frequency dividers can produce a gentler slope and a good transient response, but the amplitude-frequency characteristics are poor. Deciding the order of high and low frequency filtering should mainly consider the problem of good connection of the phase of the speaker itself at the crossover point.


Speaker classification

The shape of the speaker is varied, and the common ones are mostly rectangular. The main structure of the box is sealed box, reflective box, transmission line, passive radiator, coupling cavity and horn.

1. The closed enclosure (Closed Enclosure) is the speaker system with the simplest structure. The 1923 was proposed by Frederick and consists of a speaker unit installed in a fully sealed box. It can completely isolate the forward radiated sound wave and the backward radiated sound wave of the speaker, but due to the existence of the enclosed box, the rigidity of the resonance of the moving mass of the speaker is increased, and the minimum resonance frequency of the speaker is increased. The sound quality of the enclosed speakers is a little deep, but the bass analysis is good. When using ordinary hard folding ring speakers, in order to obtain satisfactory bass reproduction, a large-volume cabinet needs to be used. Most of the new enclosed speakers use a high Q value. Compliant speakers. Using the elastic effect of the quality of compressed air enclosed in the box, although the speaker is installed in a smaller box, the air cushion behind the cone will exert a counter-force on the cone, so this small enclosed speaker is also called an air cushion speaker .

2. Bass-Reflex Enclosure, also known as AcousTIcal Phase Inverter, was invented by Thuras in 1930. There is a sound outlet opening in its load on a panel of the cabinet. There are many positions and shapes of the opening, but most of them are also equipped with sound ducts in the hole. The relationship between the internal volume of the cabinet and the sound tube hole, according to the principle of resonance, produces resonance at a specific frequency, called anti-resonance frequency. The backward radiated sound wave of the speaker is reversed through the duct, and then radiated to the front from the sound outlet, which is superposed in phase with the forward radiated sound wave of the speaker. distortion. Ideally, the lower limit of the low-frequency playback frequency can be as much as 20% lower than the speaker resonance frequency. This kind of speaker can reproduce rich bass with a small cabinet, which is the most widely used type at present.

3. Acoustic resistance enclosure (AcousTIc resistance Enclosure) is essentially a deformation of an inverting type speaker. It is filled with sound absorbing material or structure in the sound outlet duct and acts as a semi-closed box to control the inverting function to make it buffer. , To reduce the anti-resonance frequency to broaden the bass playback frequency band.

4. The transmission line speaker (Labyrinth Enclosure) is named after the transmission line of classical electrical theory. There is a sound duct made of sound-absorbing wall plate behind the speaker, the length of which is 1/4 or 1 of the wavelength of the low-frequency sound to be raised. /8. In theory, it attenuates the sound waves coming from behind the cone to prevent it from being reflected to the open end and affect the sound radiation of the woofer, but in fact the transmission line type speaker has a slight damping and tuning effect, increasing the speaker at or near the resonance frequency Acoustic output, and reduce the amount of stroke while enhancing bass output. Usually the sound ducts of such speakers are mostly stacked in a labyrinth, so they are also called labyrinth or labyrinth.

5. Passive radiant speaker (Drone Cone Enclosure) is a branch of bass reflex speaker, also known as empty paper cone speaker. It was published by Olson and Preston in the United States in 1954. The empty paper cone (passive cone) of the magnetic circuit and voice coil is replaced. The radiation generated by the vibration of the passive cone and the forward radiated sound of the speaker are in the same phase working state. The smoothness and the quality of the passive cone form a resonance, enhancing the bass. The main advantage of this kind of speaker is to avoid the unstable sound reflected by the sound hole. Even if the volume is not large, a good sound radiation effect can be obtained, so the sensitivity is high, which can effectively reduce the working amplitude of the speaker and the impact of standing waves Small, clear and transparent sound.

6. The coupled cavity speaker is a box structure between the closed type and the bass reflex type. It was published by Henry Lang of the United States in 1953. Its output is output by the sound hole driven by one side of the cone, and the cone is another. One side is coupled to a closed box. The advantage of this kind of speaker is that the amount of air pushed by the speaker is greatly increased at low frequencies. Because the coupling cavity is a tuned system, when the cone movement is restricted, the output of the sound outlet does not exceed the sound output of the individual cone, which broadens the low frequency. Range, so the distortion is reduced and the withstand power is increased. In 1969, the A.S.W (AcousTIc Super Woofer) speaker released by Koshima Kawashima of Lo-d in Japan is a coupled-cavity speaker suitable for reproducing bass with small-diameter long-stroke speakers without distortion.

7. Horn type enclosure (Horn type Enclosure) For home use, it is mostly in the form of a folded horn (Folded Horn). Its horn mouth is coupled with a large air load at the mouth, and the diameter of the driving end is very small. The back of the box is fully sealed, and the pressure in the chamber is mostly on the back of the speaker cone. In order to maintain the balance of the front and rear pressure of the cone, the inverted horn is installed in front of the speaker. The folding horn speaker is a derivative of the inverted speaker, and its sound effect is better than the general bass reflex speaker of the enclosed speaker.


Types of speakers

1. Low-frequency loudspeaker-For various speakers, the quality factor of low-frequency loudspeaker-Q0 value requirements are different. For closed and inverted boxes, the Q0 value is generally between 0.3 and 0.6. In general, the larger the caliber of the low-frequency speaker, the diameter of the magnet and the voice coil, the better the low-frequency playback performance and transient characteristics, and the higher the sensitivity.
The structure of the woofer is mostly cone type, and a small amount is flat type. There are many types of woofer diaphragms, such as aluminum alloy diaphragm, aluminum magnesium alloy diaphragm, ceramic diaphragm, carbon fiber diaphragm, bulletproof cloth diaphragm, glass fiber diaphragm, acrylic diaphragm, paper diaphragm, etc. Bass units that use aluminum alloy diaphragms and glass fiber diaphragms are generally smaller in caliber and bear more power, while bass units that use reinforced paper cones and glass fiber diaphragms have a more accurate sound when replaying music and have a good overall balance.

2. Intermediate frequency speaker-Generally speaking, as long as the frequency response curve of the intermediate frequency speaker is flat, the effective frequency response range is larger than the width of the sound emission band it bears in the system, and the impedance is consistent with the sensitivity and the low frequency unit. Sometimes the power capacity of midrange is not enough, you can also choose a higher sensitivity, and the impedance is higher than the midrange of the bass unit, thereby reducing the actual input power of the midrange unit.
The midrange unit generally has two types: cone and dome. It's just that its size and power are larger than the tweeter and it is suitable for playing mid-range audio. The diaphragm of the midrange unit is mainly made of soft materials such as paper cones and silk membranes, and occasionally there are a small amount of alloy dome diaphragms.

3. High-frequency speaker-the tweeter is, as the name suggests, a speaker unit for playing back high-frequency sounds. Its structure is mainly divided into several types such as number solution type, cone type, dome type and aluminum belt type.

A. Due to the strong directivity of the horn-type tweeter, powerful commercial sounds can be heard on the front of the horn. They are mostly used for high-power sound reinforcement, conference speakers and a small number of monitor speakers.

B. The cone-type tweeter is too large and heavy, and the high-frequency characteristics are not as good as other types of tweeters. Therefore, it is more common in old-style speakers and has been gradually eliminated in recent years.

C. The dome tweeter is currently the most commonly used tweeter in home speakers and small monitor speakers. The dome tweeter is divided into the dome structure and can be divided into a positive dome unit and an anti dome unit; from the dome material, it is divided into two categories: hard dome and soft dome.

D. The diaphragm materials of hard dome tweeters include aluminum alloy, titanium alloy, magnesium alloy, titanium alloy composite membrane, glass membrane, diamond membrane and so on. The treble played by the hard dome tweeter has a bright tone and a metallic feel. Suitable for playing popular music, movie music and effect music. The production of excellent aluminum alloy and titanium alloy composite membrane dome tweeters can also better express classical music and vocals.

E. The diaphragm material of soft dome tweeter includes silk membrane, silkworm membrane, rubber membrane and bulletproof cloth membrane. The treble of the soft dome tweeter when replaying music is smart and relaxed, and has a very good natural expression. It is especially handy when expressing classical music, vocals and other music with standard listening concepts. Especially in recent years, the treble of silk film and silk film ball, the upper limit of playback frequency has reached 40KHZ. In theory, the upper limit frequency of the tweeter should reach at least 20KHZ, the higher the better. But the unit with excellent high-frequency upper limit is more expensive.

F. When the positive ball unit plays music, the horizontal diffusion angle is larger; when the anti-ball unit tweeter plays music, the horizontal radiation angle is smaller, but the tone is pure and the power is also greater.

If you are a classical music lover and have strict requirements for color contrast during playback, you may wish to choose a soft-ball tweeter such as silk film. If your speakers also need to take care of karaoke and play movies, it is better to choose a hard dome unit. Of course, this is not absolute, because the playback sound of the speaker is related to the design of the crossover, the manufacture of the cabinet, and many other factors in addition to the unselected unit.

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