Speaker classification Daquan Introduction to the working principle of six kinds of speakers
I. Magnetic speakers (reed speakers)
Magnetic speakers are also called “reed speakers”. In the magnetic speaker structure, there is an electromagnet with a movable iron core between the two poles of the permanent magnet. When there is no current in the coil of the electromagnet, the movable iron core is attracted by the phase-level attraction of the two magnetic poles of the permanent magnet and remains stationary in the center; When current flows through the coil, the movable iron core is magnetized and becomes a bar magnet. With the change of the current direction, the polarity of the bar magnet also changes accordingly, so that the movable iron core rotates around the fulcrum, and the vibration of the movable iron core is transmitted from the cantilever to the diaphragm (paper cone) to promote the thermal vibration of the air.
Second, ion speakers
Under normal conditions, the molecular weight of air is neutral and not charged. But after high voltage discharge, it becomes charged particles, which is called dissociation. The ionized air is vibrated by the audio voltage to generate sound waves, which is the principle of the ion speaker.
In order to ionize, a high frequency voltage of 20MHz is applied, and the audio signal piezoelectric is superimposed on it. The ion loudspeaker 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 8mm is opened in the center to form a quartz tube, one electrode is inserted into it, and the other electrode is cylindrically sleeved outside the quartz tube. Due to the silent discharge form, only the center needle electrode has wear and tear, the center electrode can be replaced periodically. The difference between the ion speaker and other speakers is that there is no diaphragm, so the transient characteristics and high frequency characteristics are good, but the structure is complicated.
III. Ultrasonic speaker
The so-called ultrasonic speaker refers to the ultrasonic sound reproduction technology that has just been successfully developed a few years ago and is entering the stage of practical use. The principle of this ultrasonic sound reproduction technology: it does not use any traditional form of speaker unit, but uses an ultrasonic generator to generate two specially treated ultrasonic beams. When these two beams act on the eardrum of the human ear at the same time, the Hearing can be produced by interaction.
We know that no sound can be heard when only one beam hits the eardrum. Due to the strong and controllable directivity of the ultrasonic velocity, the intersection of the two beams can form a sound-reproducing area with a small range. When the human ear is in this area, the sound can be heard. You can’t hear it outside the area. Taking advantage of this feature, some top luxury cars are now equipped with multiple sets of this ultrasonic sound reproduction system, forming a listening area on each seat, so that each passenger can choose the content they like to enjoy without mutual understanding No interruptions are created, and the conversation between passengers is not disturbed at the same time.
Four. Electrostatic speaker (condenser speaker)
An electrostatic speaker is a speaker that uses the electrostatic force applied to the capacitor plate. Look, because the positive and negative electrodes are opposite to each other and form a capacitor shape, it is also called a condenser speaker. The electrostatic speaker has two thick and hard materials as fixed plates, one of which can transmit sound, and the middle plate is made of thin and light material as the diaphragm (such as aluminum film). Fix and tighten around the diaphragm and keep a considerable distance from the fixed pole. Even on a large diaphragm, it will not collide with the fixed pole.
There is a direct current voltage (called the bias voltage) between the two electrodes of the electrostatic speaker. If the audio voltage output by the amplifier is applied 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 of the attractive force of the gap between the two poles, and the diaphragm vibrates and makes a sound.
The advantage of the electrostatic speaker is that the entire diaphragm vibrates in the same phase, the diaphragm is light, the distortion is small, and it can reproduce extremely crisp sound, with good resolution, clear details, and realistic sound. Its disadvantage is that it has low efficiency, requires high-voltage DC power supply, is easy to vacuum, and increases the distortion of the diaphragm. It is not suitable for listening to rock and heavy metal music, and the price is relatively expensive.
V. Air-modulated speakers (air-flow speakers)
Air-modulated speakers are speakers that use compressed air as an energy source and use audio current to modulate airflow to produce sound. It consists of air chamber, modulation valve, horn and magnetic circuit. The compressed air flow passes through the valve from the air chamber, 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, it is mainly used as a sound source for high-intensity noise environment test or long-distance broadcasting.
Six, Piezoelectric Speakers
A speaker that uses the inverse piezoelectric effect of piezoelectric materials is called a piezoelectric speaker. Dielectrics (such as quartz, potassium sodium tartrate and other crystals) are polarized under the action of pressure, resulting in a potential difference between the surfaces at both ends, which we call the “piezoelectric effect”. Its inverse effect, that is, the elastic deformation of the dielectric placed in the electric field, is called the “inverse piezoelectric effect” or “electrostriction”. Compared with electrodynamic speakers, piezoelectric speakers do not need a magnetic circuit, and compared with electrostatic speakers, they do not need a bias voltage. They have a simple structure and are cheap. The disadvantage is that the distortion is large and the operation is unstable.
