Our daily-used earphones are mainly divided into four basic structure sound units: moving coil, moving iron, tablet, and static electricity. At present, the moving coil of earphones on the market is the most used and most widely used sound unit. The working principle of the moving coil is related to Similar to the loudspeaker, a coil is attached to the diaphragm of the moving coil unit, and the changing current passes through the coil to generate a magnetic field, which interacts with the permanent magnet below to vibrate the diaphragm and produce sound. The proud Tesla technology unit increases the magnetic force density of the magnetic gap of the voice coil movement to a level of more than 1T under the limit of a certain volume. It is famous for its powerful high magnetic density unit and true colorless and low distortion sound reproduction. This new unit can convert the extra magnetic energy into acoustic energy, giving more energy to the sound. The material and diameter of the coil and diaphragm of the moving coil are also relatively large uncontrollable factors for the sound, so there will be some differences in units of different diameters and materials.
Moving iron unit is a sound unit with a very simple structure, which is another innovative evolution product of moving coil unit. According to the encyclopedia, its coil is wound on the balance armature located in the center of the permanent magnetic field. The changing current magnetizes the armature, and the magnetic field generated by the permanent magnet acts on the magnetically changed armature, thereby generating vibration. The vibrating armature transmits the vibration to the center point of the MSI diaphragm through the connecting rod, and drives the diaphragm to vibrate to produce sound. The advantages of the moving iron unit are very obvious, and it can achieve a small volume. At the beginning, it was used as the main sounding unit of hearing aids. Since it goes deep into the ear canal, it can avoid the interference of external sounds to the greatest extent. With the development of earplugs and the use of multiple frequency band moving iron units, multiple moving iron units can be integrated in the earplug cavity. The moving iron unit is easier to drive than the moving coil unit, and better resolution and instantaneousness can be obtained. State response, but also due to the volume and diaphragm problems, the low-frequency problem of moving iron units always has this "iron smell", which is not as natural as moving coil units.
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The principle of the tablet unit earphone is simply to embed the coil in the thin diaphragm, and the permanent magnets are concentrated on one or both sides of the diaphragm. The changing current in the coil in the diaphragm generates a magnetic field, which is affected by the magnetic field generated by the permanent magnet. The force is applied, thereby vibrating and making a sound. In fact, the structure of the flat panel unit is quite similar to that of the electrostatic unit. Therefore, some people say that the flat panel earphone is actually a technical application that combines the excellent high frequency of electrostatic earphones with the low frequency of the transient and natural atmosphere of moving coil earphones. Generally speaking, flat earphones have higher requirements for process accuracy.
The electrostatic unit earphone can be regarded as a major breakthrough in the sound unit. Although its structure is still not separated from the traditional sound principle structure, its unique sound principle can achieve a more realistic sound reproduction. The principle is to amplify the audio model and connect it to a fixed pole plate, and the changing audio signal will change the electric field between the two pole plates. The metal diaphragm of the earphone is located between the two polar plates, and an extremely high voltage is externally connected. In the changing electric field generated by the audio signal, the electric charge on the diaphragm is forced to cause the diaphragm to swing and form sound. The structure seems complicated, but the principle is to use Coulomb's theorem. The driving method of electrostatic earphones relies entirely on the action of electrostatic field and does not rely on magnetic force at all. However, electrostatic earphones need special amplification equipment to drive, and the relative cost is relatively high.
Because moving coil earphones are the most common and common earphones, we will focus on the introduction here to let everyone have a preliminary understanding of its craftsmanship and characteristics. The driving unit of moving coil earphones is basically a small The dynamic speaker is driven by a voice coil in a permanent magnetic field to vibrate the diaphragm connected to it. The coil in the permanent magnetic field is connected to the diaphragm. The coil drives the diaphragm to produce sound under the signal current drive. Moving coil earphones are more efficient, and most of them can be driven by the earphone output on the audio, and they are reliable and durable.
The moving coil unit has the drive modes of isomagnetism, static electricity, stasis, etc. The driver of the isomagnetism earphone is similar to the reduced flat speaker, which embeds the flat voice coil in the thin diaphragm, like a printed circuit board, which can drive The force is evenly distributed. The magnets are concentrated on one or both sides of the diaphragm (push-pull), and the diaphragm vibrates in the magnetic field formed by it. The diaphragm of a magnet earphone is not as light as the diaphragm of an electrostatic earphone, but it has the same large vibration area and similar sound quality. It is not as efficient as a moving coil earphone and is not easy to drive. Electrostatically driven earphones have a light and thin diaphragm, which is polarized by a high DC voltage. The electrical energy required for the polarization is converted by alternating current, and it is also battery-powered. The diaphragm is suspended in the electrostatic field formed by two fixed metal plates (stator). When the audio signal is loaded on the stator, the electrostatic field changes and drives the diaphragm to vibrate. The single stator can also drive the diaphragm, but the push-pull form of the double stator has less distortion. Electrostatic earphones must use special amplifiers to convert audio signals into voltage signals of hundreds of volts. The electrostatic earphones can also be driven by connecting a transformer to the output of the power amplifier. Electrostatic earphones are expensive and difficult to drive, and the sound pressure level that can be reached is not as large as that of moving coil earphones, but it has a fast response speed, can reproduce all kinds of tiny details, and has very low distortion.
Electret earphones are also called fixed electrostatic earphones. The diaphragm itself is polarized or the electrostatic field emitted by polarized materials outside the diaphragm is polarized, and no special equipment is required to provide a polarization voltage. Electret earphones have most of the characteristics of electrostatic earphones, but the electret will gradually depolarize and need to be replaced, and its life span is about 5-10 years. Inside the moving iron earplugs, the voice coil is wound on a precision iron piece called "balanced armature" located in the center of the permanent magnetic field. This piece of iron drives the diaphragm to make sound under the action of magnetic force. The moving coil directly drives the diaphragm, while the moving iron is conducted to the center point of a miniature diaphragm through a precisely structured connecting rod, thereby generating vibration and sound. In terms of unit location, the traditional moving coil earplugs cannot put the entire sound unit in the ear, while the moving iron type can be easily put into the ear canal because the unit is much smaller. This approach effectively reduces the area of the ear part and can be inserted into the deeper part of the ear canal. Since the geometric structure of the ear canal is much simpler than that of the auricle, it is a round shape, so a soft silicone sleeve has a good sound insulation and anti-leakage effect compared to traditional earplugs.
Most of the earphones can be removed by simple disassembly. Of course, if it is a violent disassembly, the process is even simpler. Usually, the outside of the dynamic earphone unit is a plastic frame, and the unit frame serves as a fixed part. At the same time, it also protects some internal components. If the unit continues to be disassembled in depth, it is easy to cause irreversible consequences. The most important diaphragm of the earphone is generally fixed on the unit frame around it, and the metal coil adhered under the diaphragm is the voice coil of the earphone, and the bottom is the permanent magnet. These four parts constitute the whole of the moving coil unit. When we use headphones, the voice coil obtains current to form a magnetic field. The permanent magnet floating below will change according to different audio signal currents, thus moving forward and backward, driving The diaphragm, the diaphragm pushes the air in front, and finally generates sound waves.
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