<3> Piezoelectric speakers: Speakers that utilize the inverse piezoelectric effect of piezoelectric materials are called piezoelectric speakers. Dielectrics (such as quartz, potassium sodium tartrate and other crystals) are polarized under pressure, causing a potential difference between the surfaces at both ends, which is called the "piezoelectric effect". Its inverse effect, that is, the elastic deformation of a dielectric placed in an electric field, is called the "inverse piezoelectric effect" or "electrostriction."
Compared with electric speakers, piezoelectric speakers do not require a magnetic circuit, and compared with electrostatic speakers, they do not require bias. They have a simple structure and are cheap. The disadvantages are large distortion and unstable operation.
<4> Ion speakers: Under normal conditions, the molecular weight of air is neutral and uncharged. However, after high-voltage discharge, they become charged particles. This phenomenon is called ionization. Vibrating the ionized air with audio voltage produces sound waves. This is the principle of ion speakers.
In order to ionize, a high-frequency voltage of 20MHz is added, and the audio signal piezoelectric is superimposed on it. It can be seen that the ion speaker is composed of a high-frequency oscillation part, an audio signal modulation part, a discharge cavity and a horn.
The discharge chamber uses a quartz rod with a diameter of 8mm to open a hole in the center and open it into a quartz tube. One electrode is inserted into it, and the other electrode is cylindrically placed outside the quartz tube as shown. Due to the silent discharge form, only the central The needle electrode is subject to wear and tear, and the center electrode can be replaced regularly. The difference between ion speakers and other speakers is that there is no diaphragm, so the transient characteristics and high-frequency characteristics are very good, but the structure is too complex.
<5> Flame speaker: When the flame of air and gas combustion passes through the electrode, the electrode is supplied with DC voltage and high-frequency signal, and the flame is modulated by the audio signal and produces sound. The flame is almost massless and the sound is dynamic. But it has fatal shortcomings: unsafe and inconvenient.
<6> Air flow modulation loudspeaker: also called air flow loudspeaker. It is a speaker that uses compressed air as energy and uses audio current to modulate the airflow to produce sound. It consists of an air chamber, a modulation valve, a horn and a 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. It is mainly used as a sound source for high-intensity noise environment tests or long-distance broadcasting.
<7> Magnetic distortion speakers. This is a special strong magnet that vibrates and produces sound under the influence of a magnetic field.
