What Is a Super Tweeter?

The belt speaker uses a layer of aluminum metal film on the magnet, and generates high-frequency signals after being energized. Band tweeters are not as durable as dome tweeters. However, the lower limit of the frequency of the band treble can be very low, and it can match the mid and low frequencies well.

A ribbon tweeter (band tweeter) uses a layer of aluminum metal film to place on the magnet and generates high-frequency signals after being energized. Band tweeters are not as durable as dome tweeters. However, the lower limit of the band treble frequency can be very low, which can be well matched with the mid and low frequencies; the advantages of the band treble: the high frequency upper limit can reach 40KHZ, easy to express more musical details, the principle is to place in a uniform magnetic field The conductive film applies audio current, and the magnetic field generated by the current and the uniform magnetic field repel and attract each other, so that the film is forced to vibrate and sound.

This process is reversible, and it is used in reverse, that is, "ribbon microphone". The conductive film is usually made of aluminum foil. Therefore, the band speaker is also called "ribbon speaker".

In fact, the band speaker and microphone were invented by the same group of scientists. The famous semiconductor scientist Walter Schottky (Walter Schottky) and his friend Siemens Halske (Siemens Halcos) obtained the relevant patent in 1923 Due to structural defects, strong magnets could not be found at the time, and the resistance and power withstanding of the film were very small, resulting in low efficiency, so it was not widely used.

In recent years, due to the widespread use of ferromagnetic materials such as neodymium magnets, the diaphragm material has also been improved from aluminum to composite materials (mostly using Kapton substrates and printed pure aluminum conductors), which has greatly improved the performance of band speakers, and the internal resistance has increased to 4- 8 ohms. It is not necessary to use a transformer to convert impedance. The power can be more than 10W, and the efficiency can be improved to more than 90 decibels. It can work well with commonly used woofers.

In traditional cone speakers, flat speakers, dome speakers, and horn speakers, although they have different structures, they all have separate voice coils and diaphragms, that is, the vertical vibration of the voice coil in the magnetic air gap passes through different forms of The diaphragm is transformed into the dense and dense change of air, forming various sounds we hear.

However, the above conventional speakers have the following drawbacks: When the voice coil receives a certain moment of electrical signal and causes the cone or diaphragm to respond, because the area of the cone or diaphragm of these speakers is large, the voice coil is only a cone. The small part of the central part of the basin or diaphragm is connected. The driving force generated by the voice coil is first transmitted to the center of the cone or diaphragm, and then gradually transmitted to other parts of the entire cone. This kind of force transmission necessarily requires a certain amount of Therefore, the force of the cone or the diaphragm is not uniform at a certain moment, and it is impossible to quickly respond to the driving force of the voice coil at the same moment, which causes the cone or the diaphragm to distort and make the speaker The reproduced sound became muddy. ^[1]

At present, the diaphragm of a band tweeter is generally a very narrow band, and its contact area with air is small, so the sound load is also small, so the electro-acoustic conversion efficiency is very low. To this end, a small horn is often added in front of it to change the acoustic impedance to improve the conversion efficiency. Furthermore, the magnetic working gap is too wide and the magnetic induction intensity is small, which results in low sensitivity.

Band tweeter structure

As shown in Figure 1, the main mountain is composed of a magnetic circuit, a voice coil, a diaphragm, and a casing.

Two strip-shaped diaphragms spread out like two wings of a butterfly. The cross-section looks like an exponential curve. Its surface area is much larger than the diaphragm of a general belt-type tweeter. Because of its large contact area with air, large acoustic load, and electro-acoustic conversion The efficiency is also high, so the sensitivity is high, and the magnetic circuit structure is shown in Figure 2. It is symmetrical left and right, up and down, but the magnetic polarity is opposite; the magnetic gap is about 0.6mm wide, which is the same as the magnetic gap of ordinary electric speakers. Therefore, its magnetic induction strength B is very high, which is beyond the reach of ordinary band tweeters. And the magnetic gap is added with magnetic fluid, which further increases the B value.

Band tweeter assembly

When assembling, the first half of the magnetic circuit is assembled and magnetized; then the half of the magnetic circuit and the other half of the magnetic circuit are connected in a magnetically opposite form. The magnetic polarity of all products should be uniform before and after. There is a magnetic short of about 1.5mm wide at each end of the magnetic gap on both sides, and its actual effect will not hinder the overall situation. The four magnetically permeable plates in the magnetic circuit can be seen to have the same shape and size. The height of the middle recessed from the two ends is exactly one half of the width of the magnetic gap. Therefore, pay attention to this size when cutting online. , Its material is low carbon steel. The magnet is a rectangular parallelepiped, and when viewed from the mountain, it is a ferrite. The voice coil in this product is a double-sided copper-clad printed circuit board with a thickness of about 0.2 mm.

The lines are formed by photolithography, and the direction, line width, and number of turns of the two sides are exactly the same. They are connected to the center of the vibration plate (voice coil), and the two ends of the printed circuit board are connected in series. 3.2. It is worth noting that the lines on the left and right sides of the vibration plate do not cut the magnetic lines of force to perform work during vibration, but instead convert the audio current flowing through it into heat, which makes the vibration plate heat up faster. In the magnetic gap, there is magnetic fluid heat dissipation and air flow during vibration of the diaphragm, which can quickly reach 150 ~ 200 ^. C's thermal equilibrium.

Therefore, we must pay full attention to this when selecting the material of the vibration plate. At the same time, on each side of each diaphragm, a flexible foam with the same curved shape as the diaphragm is used as a support to prevent the diaphragm from sinking. The diaphragm is a very soft black rectangular film with a thickness of about 0.05mm. Some are like rubber or may be a German-made PU film. The feel is smooth and soft. Its shape is as shown in Figure 5. The left side is the same as the diaphragm rubber. Sticking is just sticking two strip-shaped diaphragms on the other side of the vibration plate, and the performance indicators are similar. But the appearance is more attractive, as shown in Figure 7. In actual application, it is installed on the top of the outer side of the speaker and protected by a black barrel-shaped metal mesh cover. Its diaphragm is much longer than the single butterfly type, and it has two more diaphragms than the former, so its sensitivity is higher. There is no soft foam support on both sides of the diaphragm. The crossover circuit box is also roughly the same. It actually sounds more delicate, plump and clear, and it is indeed an advanced band tweeter. end.

The installation method of this product is the same as that of the general dome tweeter, and it is installed on the front of the speaker. The frequency division line of this speaker, its performance index f0 is 37Hz, impedance is 3.2, the effective frequency range is 37Hz ~ 16kHz, and the box volume is about 61L. ^{[1] [2]}