Tweeter technology
Most current speakers are electric speakers, and the upper limit frequency is difficult to reach 20KHZ. Let's take a look at the force of the electric speaker. The force of the voice coil to push the paper tray is F. F can be decomposed into longitudinal force Fe and lateral force Ft. Because of the presence of Ft, the cone surface of the paper tray alternately bends, which causes the tray to vibrate laterally to form a standing wave. The standing wave causes the frequency characteristics of the speaker to fluctuate at high frequencies, and the characteristic curve is not uniform enough. To overcome this shortcoming, it is to try to reduce the weight of the paper tray (reduce inertia, thereby weakening the lateral vibration) and increase the rigidity of the paper tray (reduce the bending caused by Ft on the paper tray). For this reason, people have made many improvements to the paper tray of the high-frequency speaker, such as the use of metal cymbals to make the paper tray, this paper tray is not only hard and light. In addition, the hardness and elasticity of boron are very high. It is a good material for making paper trays. First, titanium is used to make a 10-20 microns thick paper tray substrate, then the substrate is placed in a vacuum at a high temperature of 2500 degrees C , Boron is bombarded with a strong electron beam, which is evaporated and deposited on the surface of the titanium substrate. The upper frequency of the speaker produced in this way can reach 36KHZ.
To further increase the upper limit frequency of the loudspeaker, it is necessary to restructure it. There is a kind of loudspeaker with an upper limit frequency of 50KHZ adopting a band structure, as shown in Figure 2. Six permanent magnets are divided into two groups to form a magnetic circuit system. The diaphragm is made of 7-8 microns thick polymer film, which is light and soft. A 10 micron thick aluminum ribbon voice coil is attached to the diaphragm. When current flows through the voice coil, the sound membrane will generate F + and F- forces according to the direction of the current, and there is no problem of lateral force at all. Because the mass of the diaphragm is very light and the motion of the diaphragm has almost no inertia, the frequency response of the speaker is particularly good.
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