The tweeters used in commercially available loudspeakers are still dominated by the hemispherical design because the technology is mature and provides a good bandwidth, while the hemispherical tweeters include materials; silk film, aluminum metal, and even Expensive beryllium and so on. In addition to the mainstream hemispherical tweeters, there are actually many tweeters of different design types, and two of them have also begun to be adopted by manufacturers, namely aluminum band treble and pneumatic tweeter. The two are very similar in appearance, as well as a rectangular design and a protective cover. What is the difference between these two units?
The development of the aluminum tweeter was developed from an aluminum ribbon microphone in the early years. It has a square shape, but the aluminum tape treble uses a metal film as the diaphragm. The film is placed in a magnetic field, and when there is current, it will Generate vibration. Since the metal diaphragm made of aluminum is very light, the high-frequency response is excellent, and the highest frequency output can exceed the super high-pitched sound of 20 kHz or more, but the defect is easily damaged, so the aluminum belt unit must be protected.
The aluminum ribbon design provides higher frequency output performance, but under the same technology, the magnetic field strength generated between the aluminum strips is weaker than that of the general tweeter, resulting in lower output energy. However, in recent years, many tweeters have used neodymium magnet as permanent magnet, which increases the magnetic field strength and enhances the high-frequency output sound pressure. At the same time, it can further reduce the unit volume, reduce the production cost, and enable the general speaker to use aluminum. Belt tweeters, plus many manufacturers are also actively introducing aluminum belt tweeters, further pushing down the price of aluminum belt treble.
In order to improve the high-frequency performance of the aluminum tweeter, in addition to using the magnetic field strength, the weight of the diaphragm can be reduced, so that some of the aluminum belt treble is made of a lighter film such as Kapton, plus an aluminum conductive film. Therefore, the high-altitude aluminum ribbon on the market is not necessarily an all-aluminum belt, but is made of synthetic material plus metal coating. The English name is Ribbon Tweeter, or it is more appropriate to use the "aluminum belt tweeter".
The other, called Air Motion Transformer or AMT, was developed by Dr. Oskar Heil in the 1960s. The principle of sounding is completely different from that of a general moving coil unit or an electrostatic unit. The pneumatic unit transmits a piece of folded film and adds conductive metal to the bottom of the film. Under the strong magnetic field, the sound signal causes the broken diaphragm to vibrate back and forth to force the air to generate sound waves. Since the film is folded like a folding fan, the effective area of ​​the 1 Width AMT is equal to the vibration surface of an 8 å‹ unit, and the film needs only a little movement to output sufficient sound pressure. Although the pneumatic treble is similar to the aluminum treble, the vibration direction of the aluminum belt is the same as the sound direction, but the vibration direction and the sound direction of the pneumatic treble are 90 degrees.
The history of pneumatic tweeters is about 40 years old. In the 1970s, AMT's technology was officially applied to speakers, and ESS introduced the AMT-1 tweeter. Later, many companies began to make pneumatic units, among which the more famous ones include ELAC JET unit, Adam X-ART unit, ETON ER4 and so on. Thanks to the powerful neodymium magnet, the highest frequency response of the pneumatic unit is increased to 50 kHz.
Since the woofer usually requires a large air flow, the pneumatic tweeter requires a closed box, and the pneumatic tweeter is not designed to be a woofer. On the other hand, the production of pneumatic tweeters is also quite a test, including the folding of the film, resulting in the unit can not be produced in large quantities at low cost, so the speakers with pneumatic units on the market are mainly used in medium and high-end products.
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