1. Magnetic speaker (reed speaker)
Magnetic speakers are also known as "reed speakers." In the structure of a magnetic speaker, there is an electromagnet with a movable core between the poles of the permanent magnet. When there is no current in the coil of the electromagnet, the movable core is attracted by the phase attraction of the two magnetic poles of the permanent magnet and remains stationary in the center; When current flows through the coil, the movable core is magnetized and becomes a bar magnet.
As the direction of the current changes, the polarity of the bar magnet also changes accordingly, so that the movable core rotates around the fulcrum, and the vibration of the movable core is transmitted from the cantilever to the diaphragm (paper cone) to promote the thermal vibration of the air.
Second, the ion speaker
Under normal conditions, the molecular weight of air is neutral and uncharged. But after high voltage discharge, it becomes charged particles, this phenomenon is called dissociation. The vibration of the ionized air with audio voltage generates sound waves. This is the principle of ion speakers.
In order to ionize, it is necessary to add a high-frequency voltage of 20MHz, and the audio signal piezoelectric is superimposed on it. The ion speaker is composed of a high-frequency oscillation part, an audio signal modulation part, a discharge cavity and a horn. In the discharge chamber, a quartz rod with a diameter of 8 mm is opened in the center to form a quartz tube, and one electrode is inserted into it, and the other electrode is cylindrically sheathed outside the quartz tube. Due to the silent discharge form, only the center needle electrode has Loss, the center electrode can be replaced regularly.
Ionic speakers differ from other speakers in that they do not have a diaphragm, so the transient characteristics and high-frequency characteristics are very good, but the structure is very complicated.
3. Ultrasonic speakers
The so-called ultrasonic speaker refers to the ultrasonic sound return technology that has been successfully developed in the past few years and is entering the practical stage.
The principle of this ultrasonic reverberation technology: it does not use any traditional form of speaker unit, but uses an ultrasonic generator to generate two specially processed ultrasonic beams. When these two beams act on the eardrum of the human ear at the same time, Hearing can occur due to interaction.
We know that when only one beam acts on the eardrum, no sound can be heard. Due to the strong and controllable directivity of the ultrasonic velocity, the intersection of the two beams can form a small range of reverberation area, when the human ear is in this area, you can hear the sound, and once the human ear You can't hear it when you leave the area.
Taking advantage of this feature, some of the top luxury cars are now equipped with multiple sets of this ultrasonic reverberation system, forming a listening area in each seat, so that each passenger can choose to enjoy the content they like without mutual mutual There will be no interference, and it will not affect the conversation between passengers.
Four, electrostatic speakers (capacitive speakers)
The electrostatic speaker is a speaker that works by using the electrostatic force applied to the capacitor plate. As far as its structure is concerned, the positive and negative electrodes form a capacitor, so it is also called a capacitive speaker.
The electrostatic speaker has two thick and hard materials as fixed plates, which can transmit sound, and the middle plate uses a thin and light material as a diaphragm (such as an aluminum film). Fix and tighten the periphery of the diaphragm to maintain a considerable distance from the fixed pole. Even on the large diaphragm, it will not touch the fixed pole.
The original DC voltage (called bias voltage) between the two electrodes of the electrostatic speaker. If the audio voltage output by the amplifier is added between the two electrodes, it overlaps with the original output voltage to form an alternating pulsating voltage. This pulsating voltage is generated by the change in the attractive force of the gap between the two poles, and the diaphragm vibrates and sounds.
The advantage of the electrostatic speaker is that the entire diaphragm vibrates in phase, the diaphragm is light, and the distortion is small. It can reproduce extremely crisp sound, with good resolution, clear details, and realistic sound. Its shortcomings are low efficiency, high-voltage DC power supply is required, easy to vacuum, the increase of the diaphragm distortion will also increase, not suitable for listening to rock, heavy metal music, the price is relatively expensive.
Five, air flow modulation speaker (air flow speaker)
The airflow modulation speaker is a speaker that uses compressed air as an energy source and uses audio current to modulate the sound of the airflow. It consists of air chamber, modulation valve, horn and magnetic circuit. The compressed air flow passes from the air chamber through the valve and is modulated by the external audio signal, so that the fluctuation of the air flow changes according to the external audio signal. At the same time, the modulated air flow is coupled through the horn to improve the efficiency of the system.
Generally used mainly as a sound source for high-intensity noise environmental tests or long-distance broadcasting.
Six, piezoelectric speakers
Loudspeakers that use the inverse piezoelectric effect of piezoelectric materials are called piezoelectric loudspeakers. Dielectrics (such as quartz, potassium sodium tartrate, and other crystals) are polarized under pressure, causing a potential difference between the surfaces of the two ends, which we call the "piezoelectric effect." Its inverse effect, that is, the dielectric placed in the electric field will elastically deform, is called "reverse piezoelectric effect" or "electrostriction".
Compared with electrodynamic speakers, piezoelectric speakers do not require a magnetic circuit, and do not require bias voltage compared with electrostatic speakers. The structure is simple and the price is low. The disadvantage is that the distortion is large and the operation is unstable.
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