Speaker Construction and Unit Types

Ⅰ. What does a speaker consist of?

Speakers are generally composed of three parts: magnetic circuit system (T yoke, field plate, magnet and back cover), vibration system (voice coil, paper cone, elastic wave and dust cap) and support system (terminal and basin frame).

1. Magnetic circuit system

(1) T yoke

It plays a role in magnetic conduction in the magnetic circuit. The iron core should actually be called Yoke. According to its shape, we can divide it into U-shape and T-shape.

(2) Field Plate

The field plate is also called the washer or the upper plate. In the magnetic circuit, both the iron sheet and the iron core play the role of magnetic conduction. They can concentrate the N pole and S pole of the magnet to the gap through the loop, so that the gap generates a stronger magnetic field.

(3) Magnet

It is the main component of the magnetic circuit and provides the magnetic field for the speaker system. Permanent magnets are broadly classified into three types: alnico-based permanent magnets, ferrite-based permanent magnets, and rare-earth permanent magnets.

(4) Back cover

Its main function is to prevent the magnet from radiating magnetic fields. It can feed back the S pole magnetic field line of the rear magnet to the iron sheet through its own magnetic conduction, which can enhance the magnetic force of the iron sheet magnetic pole. This shows that the back shell can not only absorb magnetism, but also effectively utilize the absorbed magnetism. Just like the requirements for the thickness of the iron core and iron sheet, we also have certain requirements for the material and thickness of the back shell. Typically, the thickness of the back shell material is 0.8 to 2.0. Under the same material, when it becomes thicker, it will have better magnetic absorption effect. Because of its high cost, we should take both into consideration and choose the best state when designing.

2. Vibration system

(1) Voice Coil

The voice coil is the most critical component of the speaker. After the voice coil conducts electricity, within the magnetic field, Fleming's left-hand rule produces movement, which drives the vibration plate.

(2) Paper Cone

The paper cone is also called sound film, drum paper, and vibration plate. It is one of the main parts of the speaker. It has a decisive influence on the performance and sound quality of the SPK. Generally speaking, a good speaker cannot be made without good drum paper. The material of the sound film can be roughly divided into three types: paper (pulp, fiber), resin (polyester-based, phenolic resin-based), and metal plate. At present, most of the vibration plates for speakers are made of paper, but for corner speakers, metal plates or resin-based products are mostly used as vibration plates.

(3) Elastic Wave 

The elastic wave is also a damper, which has a braking effect and a center holding effect. The outer edge of the spring is glued to the bracket. The neck of the sprung is glued to the bobbin of the voice coil and the neck of the drum paper. The performance of the elastic wave is similar to that of the flange of the drum paper, which affects the bass resonance FO, has a moderate elastic assisting effect on the connection of the diaphragm, and can control the operation of the mode direction of the diaphragm.

(4) Dust Cap

The dust cap is mainly to prevent dust and other sundries from entering the magnetic gap from the front of the vibrating plate to cause abnormal sound, and at the same time, it has the function of reinforcing the treble. Most of its materials are paper, cloth, non-woven fabric, Mylar, PEI and metal film. However, since paper, Mylar, PEI and metal films all reinforce the vibration plate, and there is also sound radiation from the dust cover, its size and shape have an impact on the cycle wave number characteristics. There are also various colors of the dust cover. When designing, we need to choose according to the customer's requirements or appearance. The plastic film or metal film dust cover has a certain degree of elasticity due to the material itself, and its thickness will affect the sound. Generally, for speakers with high power and strong vibration, the thickness of the dust cover should be correspondingly thicker to prevent resonance.

3. Support system

(1) Terminal 

The function of the terminal is to transmit the external signal to the wire, and then enter the voice coil, so that the coil obtains current. At the same time, the PIN of the terminal fittings has its standard specifications, which is beneficial to the direct insertion of external plugs.

(2) Basin Frame

It is the mother body for installing vibration parts, magnetic circuits and other parts. The brackets of small SPK are all steel plates, made of SPCC. The steel plate is stamped and formed with a thickness of 0.5~1.2MM. The surface is usually treated with colorful electroplating, baking black, electric black, and rust prevention. Large-diameter magnetic circuits are particularly strong and bulky, and the steel plate material will be 1.0MM or even thicker. But the advanced HI-FI SPK also has a cast aluminum bracket. In addition, there are many brackets made of plastic, among which waterproof speakers and headsets are the most commonly used. The material of the plastic frame is mostly ABS or ABS fiber-added to increase resistance and strength.

Ⅱ. Parameter description of speakers

1. Re: It refers to the DC resistance of the voice coil.

2. VAS: It refers to the volume of air with equivalent flexibility of the monomer. This value determines the size of the speakers to be used.

3. MMD: It refers to the equivalent quality of a single vibration system.

4. SD: It refers to the effective vibration area of the single diaphragm.

5. VAS: It refers to the volume of air equivalent to the flexibility of the monomer, in liters (L).

6. CMS: It refers to the compliance of the supporting components of the vibration system. The larger its value, the softer the entire vibration system of the speaker.

7. MMS: It refers to the total mass of drum paper, elastic wave, voice coil, dust cap and air during vibration. This value is related to FO and sound pressure.

8. QMS: It reflects the amount of mechanical damping state of the suspension system of the speaker FO. Actual tests show that it also affects the mid- and high-frequency performance of the speaker.

9. QES: The electrical Q value of the monomer. This value can confirm the matching of speaker parts, such as the voice coil design value and position setting, and the magnetic circuit. It is jointly determined by the MMS, CMS and BL of the vibration system.

10. QTS: It reflects the damping state of the vibration system near the speaker FO and is an important parameter that determines the low-frequency characteristics of the speaker. The smaller the QTS value, it shows that the suspension system and electrical damping can better control the performance of the unit and produce a smaller amplitude at the resonance point of the system.

11. SPLO: It refers to the sound pressure level, the unit is decibel (db).

12. FO: It refers to the resonant frequency of the monomer in free atmosphere, the unit is Hertz (HZ). It is related to the performance of the speaker at low frequencies. Components that affect this value include drum paper, elastic waves, voice coils, etc. If FO is too low, distortion will increase.

13. ZMAX: It refers to the impedance value corresponding to the peak point of the monomer impedance curve, and the unit is ohm (0hm/Q).

14. ACR: It refers to the AC impedance, which is the impedance corresponding to the lowest point after the peak value of the speaker impedance curve. The unit is ohms.

15. BL: It refers to the power of the monomer. It is related to the magnetic circuit of the speaker. It is equal to the length of the voice coil wire in the magnetic field multiplied by the magnetic flux density.

Ⅲ. Types of speaker units

1. Ribbon speaker unit

The principle of the ribbon speaker unit is to apply an audio current to a conductive film placed in a uniform magnetic field. The magnetic field generated by the current and the uniform magnetic field repel and attract each other, causing the film to vibrate and produce sound. The diaphragm of the ribbon speaker unit is mainly made of aluminum alloy or polyimide film, and the most common ones are aluminum alloy.

Its structure is composed of strip magnets forming a magnetic gap for N and S bipolar sounds, and an ultra-thin aluminum strip serves as both a diaphragm and a voice coil (the aluminum strip is both a conductor and a vibrator) placed in the magnetic gap. When the audio current is sent to both ends of the aluminum strip, under the action of the magnetic field lines, the aluminum strip vibrates with the change of the audio current, thus completing the process of converting the audio signal into sound.

Ribbon speaker units mainly reproduce medium and high frequencies. Because the aluminum strip is very light and thin, the number of vibrations per second will be very high and it can reproduce very high frequency sounds (up to 40 kilohertz). Therefore, it has fast response speed, small distortion, and flat and uniform frequency response. Diffusion and layering are good. It has excellent high-frequency characteristics, pure tone, and can produce high-pitched sounds with extremely high clarity, extremely fast transient response, and very small phase distortion. However, the manufacturing process of ribbon speaker units is complicated, production is difficult, and adjustment is difficult.

2. Cone speaker unit

It has simple structure and high energy conversion efficiency. Cone speaker units are mainly divided into four types: treble, midrange, bass and full-band. The basic structure of each type is the same, but the caliber and diaphragm material are different. However, the cone tweeter unit has been basically replaced by dome and horn tweeter units due to its small radiation surface and low accuracy.

Many of the diaphragm materials of cone speaker units are mainly pulp materials, which is what we usually call "paper cone". The pulp will also be mixed with materials such as wool, silk, and carbon fiber to increase its rigidity, internal damping, and waterproof properties. The sound of the paper cone is smooth and natural, and it has good performance in terms of instantaneous response and hearing details, but its moisture resistance is poor, so other materials are added to improve its performance. However, many high-end speakers still very much favor paper cones.

In addition to the paper cone, the cone cone speaker unit will also use composite materials such as polypropylene, ceramics, mica carbonized polypropylene, carbon fiber textile, bulletproof cloth, hard aluminum foil, CD corrugation, glass fiber, etc. to further improve its performance. For example, ceramic pots have very detailed representations of human voices and classical music. In terms of mid-bass, it has good transients and dynamics, excellent bass and accurate positioning.

3. Horn speaker unit

It works on the same principle as a cone, it just radiates sound differently. The cone speaker unit radiates sound directly from the diaphragm, while the horn speaker unit vibrates the diaphragm and then diffuses the sound through the horn, which is an indirect radiation type.

4. Haier speaker unit

In 1973, Oscar Heil of the United States invented a special speaker sound wave radiation method, namely AMT (Air Motion Transformer). Its working principle is that there is a special insulating film between the two magnetic poles. The surface of the film is covered with a layer of metal coils arranged in a certain direction, and the diaphragm assembly is folded like an accordion. Each adjacent surface of the folded diaphragm makes relative motion in the magnetic field, squeezes or sucks air from the folds, and radiates sound waves in the form of jets.

Its production process is complex, its price is high, and its penetration rate is not very high. It can only be seen in high-end products of a few famous brands, such as ELAC, ADAM and Burmester from Germany, GRYPHONG from Denmark, Mark Daniel from the United States, and Shenghui from China. .

However, compared to other types of speaker units, the advantages of Haier speaker units are very obvious. Firstly, its diaphragm area is large, with a 1-inch dome tweeter having a diaphragm area of approximately 506 square millimeters. However, the diaphragm area of the Haier tweeter unit after unfolding is approximately 4500-6900 square millimeters, which is 8-13 times that of the dome tweeter unit. Naturally, the amount of driving air is more than that of the dome tweeter unit. Therefore, its sound coverage is greater. Secondly, due to the relative motion of each adjacent surface of Haier's high pitched folded diaphragm. When driving the same volume of air, the diaphragm requires much smaller amplitude and faster speed. Therefore, high-frequency extension is better, and the transient reaction speed is also faster. Thirdly, the impedance curve of Haier's speaker unit is flat, easy to drive, and has lower distortion.

5. Flat speaker unit

The core of a flat speaker unit is a flat diaphragm. It is made of a light and rigid honeycomb flat plate or foam resin filled in a rigid metal cone diaphragm. At present, the application of flat-panel speaker units has been very extensive. We can see it in home theater systems, KTV high-power flat-panel audio, background music public broadcasting systems, multimedia computer audio, charging Bluetooth wireless flat-panel audio, and charging card radio flat-panel audio systems.

Flat panel speakers have many advantages over traditional speakers. First of all, its sound distortion is very low, the sound quality is more transparent and pure, the treble is clear and delicate, and the sound attenuation is small. Secondly, the sound directivity of the flat-panel speaker unit is very good. Since the sound is evenly emitted from the entire plane, rather than the point sound source of the traditional speaker, the diffusion of the sound wave is diffuse, so the sound field is wide. At the same time, there is no "sweet spot" for flat panel speakers. We hear the same sound no matter where we are in the room. Even if two flat-panel speakers are placed together, the sound quality will not be greatly affected, so it does not have strict placement restrictions. In addition, the flat-panel speaker eliminates the box and baffle of traditional speakers, so the phenomenon of "sound coloration" is completely eliminated, so the sound performance is more accurate, smooth and natural. Coupled with the ultra-thin special construction, it takes up almost no space, making it very easy to place.

6. Dome speaker unit

The working principle of dome speaker units is similar to that of cone speaker units. However, its diaphragm is an approximately hemispherical spherical surface, and its diaphragm size is small. It is mostly a treble or mid-treble unit, so it is used in conjunction with a cone woofer unit. The basic structure of the dome tweeter and the dome midrange unit is the same, but the latter has a larger rear cavity and is usually filled with some sound-absorbing material, which prevents the diaphragm from being depressed, dampens low-frequency split vibrations, and prevents in-cavity Standing waves appear.

(1) Hard dome and reverse dome aluminum film speaker units

The dome tweeter is currently the most commonly used tweeter in home and small monitor speakers. From the perspective of dome structure, it can be divided into positive dome unit and reverse dome unit. According to the dome material, it is divided into two categories: hard dome and soft dome. When the positive ball unit plays music, its horizontal diffusion angle is larger; when the reverse ball tweeter plays music, the horizontal radiation angle is smaller, but the tone is purer and the power it withstands is larger.

The diaphragm materials of hard dome tweeters include aluminum alloy, titanium alloy, beryllium alloy, magnesium alloy, glass membrane, diamond membrane, etc. Its tone is bright and metallic. It is suitable for playing pop music, movie music and effect music. Made of excellent aluminum alloy and titanium alloy composite membrane dome tweeters, it can also better express classical music and vocals.

(2) Soft dome and full dome silk speaker units

The diaphragm materials of soft dome tweeters include silk membrane, silkworm thread membrane, rubber membrane and bulletproof cloth membrane. The soft dome tweeter reproduces music with relaxed highs and good natural expression. It is particularly suitable for expressing classical music, vocals, etc. that have standard listening concepts.

Ⅳ. Precautions for using speakers

1. Install the speaker correctly, making sure it is placed stably to avoid vibration and friction.

2. When adjusting the speaker volume, increase or decrease it gradually to avoid sudden volume changes.

3. Do not place the speaker in a humid or high temperature environment to avoid affecting the sound quality.

4. Do not place the speaker in a dusty environment and clean the dust cover regularly.

5. When using the speaker, we avoid pulling the wire hard to avoid damage.

6. Do not place corrosive or flammable objects close to the speaker to avoid affecting its service life.

7. We should regularly check whether the speaker's power cord and plug are intact, and replace them in time if they are damaged.

8. Please prevent iron filings and other metal debris from being adsorbed on the speaker to avoid abnormal working sound.

9. Do not use thinner or other chemical cleaners to clean dirt on the product (use an air gun to blow dust).

10. Please ensure that the speaker is used under the conditions specified in the product specification.

In order to ensure that the speaker can perform its function normally, maintain good sound quality, and prolong its service life, users must pay close attention to the above problems. Failure to comply with the above regulations may result in damage to the speaker. Therefore, we strongly recommend that users strictly abide by these regulations to ensure that the speakers can continue to provide excellent sound quality and use experience.