We know that in the loudspeaker, when the voice coil is connected to the audio signal, it will produce strong vibration in the magnetic field. The voice coil is fixed on the loudspeaker cone. The vibration of the voice coil will drive the vibration of the speaker cone at the same time. The vibration of the speaker cone forces the air to vibrate, so as to produce sound. Therefore, the speaker cone is an important part of the speaker, and the sound quality is different with different speaker cone materials.
Classification and characteristics of loudspeaker cone
At present, the speaker cone on the market can be roughly divided into the following categories:
1. Paper cone: the paper cone is easy to integrate with other materials, so there are several kinds of paper cones, such as coated paper cone and tight pressed paper cone. Although the cost of paper cone is low, its timbre performance is good and its sensitivity is high. So the paper cone is the most widely used.
2. PP cone: PP cone has low distortion, is good at performing all kinds of music, and has high cost.
3. Wool cone: using wool as loudspeaker cone, with good flexibility, good at performance of light music.
4. Bulletproof cloth cone: the speaker of bulletproof cloth cone has a wide range of frequency response, which is suitable for music lovers who like strong bass. But its cost is high and it is difficult to make.
5. Ceramic cone: good at performance of voice, classical music, fine timbre, good dynamic performance.
Metal cone: add aluminum, magnesium and other metal elements, strong rigidity. The loudspeaker has strong instant explosive power and is suitable for dynamic and powerful music.
Material analysis of speaker cone
1. Paper materials
Paper material is the traditional material for making speaker cone, which is often mistaken as outdated technology and is not suitable for the use of high-performance speakers. The paper speaker cone is easy to be processed into various shapes without complicated and expensive molds, and its mechanical properties can be adjusted in a wide effective range. However, untreated paper cones are very sensitive to the environment, especially humidity. When the environmental humidity changes, the paper moisture will change, resulting in the changes of carcass quality and Young's modulus and other parameters.
In addition, although it is possible to process a loudspeaker cone with enough rigidity to obtain an extended frequency response range, the internal loss of the paper itself is not enough to obtain a smooth roll off. In addition, the deviation of paper production is large, which is not conducive to the consistency of batch products. The application of various surface treatment methods can overcome the above two shortcomings, such as latex or PVA based coating, impregnation. These coatings help to isolate the speaker cone from the surrounding environment and increase the transmission loss, so they can smooth the high frequency response.
2. Polypropylene materials (also known as PP, CD, etc.)
The BBC developed the material in 1976. Because of its strong internal damping, it can obtain a flat response and high efficiency in the working area without any equilibrium. Polypropylene is probably the most common material for loudspeaker cone application. Many speaker cones, which are claimed to be made of polypropylene, are actually doped with organic compounds and other fillers (such as carbon fiber and Kevlar). Fillers can control costs and change the mechanical properties of materials. Polypropylene speaker cone has good inherent damping, so as long as the frequency band requirement is not very wide, it is no problem to achieve smooth response. In addition, it is not sensitive to environmental humidity. It is easy to achieve strict tolerance control of the material itself and its processing technology. In fact, because of its stable and reliable properties, polypropylene materials are the first choice for many researchers to carry out FEA analysis of loudspeakers. Polypropylene materials are not easy to bond, so they should not be approved in the early days. Modern advanced adhesion technology (early 1980s) has completely solved this problem.
3. High strength woven fiber with resin
Most carbon fiber, glass fiber and Kevlar basins belong to this class. The speaker cone is made of fiber woven cloth and epoxy or similar resin. The fiber itself has a very high tensile strength, and the hardness of the material will be considerable if a proper amount of resin is implanted. There is no doubt that the frequency band of the braided basin has expanded. However, the smoothness of the frequency response will be affected because of the low internal loss. It is believed that the irregular orientation of the fiber is beneficial to the suppression of the standing wave in the basin and the smooth frequency response. According to experience, this method has little effect on the high frequency response, and the high frequency response of the test speaker is not smooth. Even the best Kevlar and carbon fiber have a high Q peak at least in the upper part of the working area, generally at the most sensitive 3-5KHZ of human ear. The same is true for other rigid elements such as metal basins, which will lead to fatigue of listening for a long time and compression (concealment effect) of sound field perspective.
4. Metal materials
Metal material is a new kind of cone material. Among the materials discussed so far, the damping of metal is the smallest, so the peak value of high frequency area is very large. It is common for 6.5-inch loudspeaker to reach 12dB peak value at 5KHz. However, under the first segmented vibration, the performance of metal voice basin is very good, which is the main point of its popularity. The most common metal voice coils are aluminum (and its alloys) and magnesium. If it is possible to use a variety of forming and surface treatment technologies to process metal materials, the emergence of high-performance metal speaker is not unimaginable. However, even if the best divider design is adopted, the current high frequency band of metal voice basin is not ideal, so it is not suitable for full band system application.
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