Diaphragm material on the loudspeaker cone

Q: what is the best material for the use of a cone?

Answer: (Jian Duan) no best material.

(in detail) the people who buy the speaker must know that the diaphragm material of the speakers is varied, and the manufacturer claims that it has some advantages, and is better than the other. Although the publicity of the people are trying to make you believe that he used the material is the best, unfortunately, in the application of the speakers, there is no single best film material. Different materials have different mechanical and acoustic properties, which make it suitable for different occasions, performed better or worse. The choice of every kind of material almost always means a certain degree of compromise.

The basic parameters that affect the acoustic performance of the vibrating membrane materials are: density, rigidity and internal loss (internal damping). Not strictly speaking, the harder the material, the lighter, the wider the frequency band, the greater the internal loss, the more smooth the response. However, the above parameters are mutually affected, and it is very difficult to realize the optimization of the three parameters at the same time. Want to know the reason why in, need to know how to produce music when the vibration of the vibration situation.

In the low frequency part, the basic motion of the conical diaphragm is basically done by the piston movement, and only one parameter has a significant influence on the speaker. [as mentioned above, if not to mention other mechanical properties have a subtle influence on low frequency characteristic of cone diaphragm, it is defective. However, for this topic, a lot of views, and further research and exploration of these views is less. If other parameters are same, the higher the quality of the cone is, the lower the resonance frequency of the speakers, the worse the resonance damping (Qe), the lower the sensitivity. Other parameters such as the CIS and mechanical loss of the supporting system also affect the resonance, damping characteristics and sensitivity of the loudspeaker. These factors should be considered in the design and analysis. The mathematical description of the low frequency characteristics of the loudspeaker is not very complicated, so it is quite simple to establish the mathematical and physical model of the low frequency section.

At a higher frequency range (when the acoustic wavelength is close to the radius of the film), the motion of the cone is no longer a single integrated vibration, and the low frequency model is no longer applicable. You'd better imagine the sound of sound waves from the beginning, after the sound coil skeleton, the pyramidal diaphragm (that is, the voice coil skeleton / diaphragm joint) began to spread around the cone film, sound waves reach the conical diaphragm, and then back to the cone diaphragm frame, and then hit the sound circle skeleton, and then back to the sound basin edge, and so repeat. This process is similar to the sound wave propagation in a house, and the wall, reflected back, and so on. In the two case, there are obvious standing waves, such as not to take certain measures, the standing wave will make the sound pressure response to produce a very clear peak valley. For example: a good 6.5 inch speaker, its first standing wave resonance occurs frequently in the middle frequency band, just in its working range, the output of a two-way system is very large.

Fortunately, most of the cone diaphragm material is not perfect sound conductor, there is a certain internal loss. In the process of sound propagation, a part of the energy is converted into heat, and the sound waves gradually decay. In order to reduce the intensity of the standing wave by absorbing the energy of reflected wave, the response tends to be smooth. Diaphragm material is different, there is a great difference in the internal loss, metal materials, plastic material is very large.

Suppression of the standing wave is another way of using the fold ring. A loudspeaker, a folded ring of the vibrating membrane of a loudspeaker, commonly used to have a rubber like elastomer or foam, and sometimes with a fold of cloth or paper. One of the functions of the folding ring is to allow the cone to provide air tightness when the film is relatively free to move in the lower frequency range. In the high frequency band, the folded ring can absorb some of the standing wave energy. The acoustic wave is transmitted through the neck of the diaphragm and the interface between the broken ring and the vibrating membrane. Some of the energy actually has been transmitted to the folded ring material, and the remaining energy is reflected back to the diaphragm. That part of the energy that is transmitted to the fold may be converted into heat (to achieve effective suppression of resonance), or rebound, and then reflect back to the vibrating membrane (resulting in a series of more complex resonance), which depends on the internal loss of the ring material. The inner loss of synthetic rubber is very high, and it does not rule out a small number of low loss. The loss in the ring is generally lower than that of the rubber, but I also believe that some people will design a high loss of foam. Whether it is a rubber or foam fold ring ring (sound basin is also the same), the internal damage may vary with frequency.

The optimum damping degree (amount) of the cone diaphragm and the fold ring is determined according to the requirements of the occasion. Overall, unless all of the standing wave resonance is produced in the effective working band of the speaker, you should ask for the vibration of the film carcass and the folded part of the composite have adequate internal loss, which can produce a smooth, controlled high frequency response. Another scheme that produces a smooth response is that the use of an active or passive equalizer for resonance compensation. But this method is not good, because the actual frequency of specific products will be affected by the production and environmental conditions, the location will be a deviation. One day for a speaker's compensation circuit, the other speaker may not be applicable.

The effective bandwidth of the cone is largely determined by the first standing wave, and the faster the acoustic wave propagation in the conical diaphragm is, the higher the frequency of the segmentation is. The main mechanical properties of the main mechanical properties of the acoustic propagation velocity are the rigidity of the material, the density and the thickness of the material. Hard, light, thick diaphragm, the sound speed of the film, and vice versa, soft, heavy, thin sound speed is slow. However, unfortunately, the general trend is lighter materials, more hard (to produce the frequency band is wide), internal loss usually smaller, also is to inhibit the ability of standing wave more low, frequency response is not smooth. In addition, the difference between the material and the material of the cone is more (the acoustic impedance mismatch), such as: the system of the hard metal sound basin and the soft elastic body, the reflection is large, the energy of the folded loop is smaller, and the effect of restraining the standing wave is worse. These characteristics make the vibration film at the same time to meet the frequency band width and smooth response to the more difficult. It is also more annoying: the greater the loss of the ring material, the greater the linear difference in the large stroke, when the low frequency signal will occur when the large signal will occur (visco elastic body in the hysteresis phenomenon, recovery time). Therefore, in the same time to achieve a smooth broadband, while you have to pursue a good low frequency performance, it will be very difficult for you, but no one will give up the pursuit of both solutions.

The above may have not been left out to describe the characteristics of the speakers of all aspects of the film, but has covered the main aspects of these topics such as further in-depth, it can be a few books.

Q: what are the characteristics of a variety of commonly used cone?

1、Paper material

Paper material is a material which is traditionally made in the film. It is often used as an out of date technology. It is not suitable for high performance speakers. The advantages of paper cone film are easy to be processed into various shapes, and it does not need to be complicated and expensive, and its mechanical properties can be adjusted in a wide range of useful range. Unfortunately, the paper cone diaphragm is very sensitive to the environment (especially humidity). When the humidity changes, the moisture content in the paper will be changed, resulting in the change of the parameters of the carcass quality and Young's modulus. Also although there may produce sufficiently rigid cone diaphragm, obtain a wide frequency response range, but paper itself in the loss is not enough to obtain a smooth rolloff characteristics. Also, the deviation of paper production is relatively large, is not conducive to the consistency of the bulk product.

Application includes a variety of surface treatment methods, such as PVA (polyvinyl alcohol) coating and impregnation, which can greatly alleviate the above two problems, which is conducive to the sound and the surrounding environment, while increasing the transmission loss, so that the frequency response of the smooth element high frequency section. Other fibers, such as carbon fiber, can also improve the acoustic properties of the film. At the same time through the control and selection process strictly, the inconsistency of paper production will improve. Please note, some manufacturers in order to satisfy the aesthetic needs of, in some paper diaphragm surface sprayed some day know the material God-only-knows, but deliberately claims of loudspeaker performance improvement of special effects. Only God knows (God-only-knows, may also damage). Please believe in science, not superstition. As for the improvement of the product's discrete nature, it can control the quality of the production process and the source material.

The same pulp, internal structure is also due to the paper method, dehydration, drying method and so on completely different, the physical constants will change. The natural fall in the form of a copy of the paper is the same as the forced absorption, even though the quality of the carcass is the same, the thickness and the density of the former is small, the young's modulus is small, and the internal loss is increased. Pulp cone is used for more than half a century. The reason is that the fiber type is rich and the internal structure can be freely controlled. Other plastic sheets or metal foils have no freedom, only to change the shape.

Although the surface of the paper material appears to be a low tech material, the paper can be used in a proper processing of paper cone, but it can also get good bandwidth and smooth response, which is comparable with the high-tech materials. Experts in the study of new paper cone membrane of the formulation, processing and surface treatment method. So don't be surprised, cheap, cone diaphragm technology old-fashioned paper materials are based on the latest breakthrough, revitalized.

2、Polypropylene material (commonly known as PP)

1976 BBC developed this material to replace BEXTENE. Because it has a very strong internal damping, the design of appropriate polypropylene unit without any equilibrium can be obtained in the working area of flat response, the efficiency is also higher.

Polypropylene material is probably the most common material used in the application of the loudspeaker cone. Most of the cone membrane, which is claimed to be made of polypropylene material, is in fact a doped mineral or other filler (e.g., carbon fiber and Kevlar). Filling material can control costs, but also change the mechanical properties of the material. The natural damping of the polypropylene film is good, so as long as the band is not very wide, to achieve a smooth response is not a problem. In addition, it is not influenced by environmental humidity, and it is easy to realize the strict control of the material itself and the error of the machining process. In fact, because of its stable and reliable properties, polypropylene is the preferred material for the finite element analysis (FEA) for many researchers.

Since polypropylene material is not easy to glue, so early and can not be recognized. The development of modern adhesive technology (80 s) has been fully resolved.

Now, the Response ProAC 3 and System Hales 2 signature version of the various speakers are using polypropylene unit, the final quality of such units mainly depends on the shape of the cone and the addition of polypropylene.

Advantages: if the design is correct, it can get a flat response, very low sound staining, good pulse response, frequency divider can be very simple, high efficiency, segmentation vibration appear slow. Good quality products can be done with the best paper pot is quite transparent.

But this is not to say that the use of polypropylene material is not a problem. Although the quantitative research papers have not been published (at least I do not know), many people think that the film can be heard from the cell membrane of the unit of viscous or similar viscous performance (Hysteresis, viscous as a nonlinear phenomenon, reflected in the system parameters will be based on the system's recent history and continued to change.) The most common that viscosity is caused by the viscoelastic creep of plastic material (called creep and viscoelastic creep is refers to the plastic material in slow spreading trend under the pressure. The process may be linear or nonlinear, depending on the material loss. Some people think that the viscosity is by voice coil skeleton and the vibration film is followed by an, voice coil heat, by voice coil rack diffusion, softening plastic sound basin or where the binder, softening depends to the voice coil dissipation of heat. As a result, the analytic power of a lot of polypropylene is not a good match with the popular metal ball.

In spite of the fact that there is actually a problem, the high frequency response and consistency of the polypropylene film material is still very popular in the high performance speaker system.

3、Other plastic materials

In addition to polypropylene (PP), in recent years, there have been a lot of plastic and plastic materials, including HD-A, HD-I, TPX (more than by Audax production), Neoflex (Focal production), Bextrene (a kind of wood pulp synthesis of plastics, BBC1967,, as a better consistency and predictability of materials to replace paper, has now been replaced by PP).

The emergence of new materials suggests that experts are working to find the best combination of rigidity, internal damping, density and sound velocity in a specific situation. The advantages of these materials are similar to those of the potential defects of polypropylene.

4、Resin bonded high strength woven fiber

The majority of carbon fiber, glass fiber and fiber (Kevlar?) of the cone film vibration. The type of the conical vibrating membrane is made of a fiber cloth with epoxy or similar resin bonded. Fiber itself has a very high tensile strength, with a suitable resin, the material will be quite rigid. Undoubtedly, the frequency band of the woven basin is extended. However, the price is not too smooth frequency response, because the loss of resin bonded materials is very low. Some people think that the irregular orientation fiber is conducive to the standing wave pattern in which failure cone, smooth frequency response. With experience, this phenomenon has a small effect on the high frequency response of the unit, we have tested the weaving basin speaker unit, high frequency response is not smooth.

Even the best KEVLAR, carbon fiber is at least a high Q peak in the upper section of the working area, the most sensitive 3-5KHZ in the human ear. Other rigid elements such as metal sound basins are also such that this will result in a long time to listen to the fatigue and the sound of the sound field of perspective of the compressive sensing (hidden effect).

Many speaker manufacturers have been trying to improve the basic structure of simple woven fiber cone diaphragm. One manufacturer uses the upper and lower two layers of bulletproof (Kevlar) fiber, the middle is the combination of resin and small silicon ball joint and a composite. The layered structure is said to be very good, and the sandwich material can control the damping capacity. Another speaker unit manufacturers using a similar sandwich, with Nomex honeycomb sandwich. These techniques are very encouraging, however, the cost is very expensive, but the other simple materials and other simple materials, high frequency response is not smooth, but the extent of the difference.

Woven fiber basin is unlikely to have a viscosity (folding ring and the centering support chip and magnetic circuit system may still have, but this is another topic. For broadband applications, it may not be the preferred material, but its inherent rigidity and non - easy to produce the characteristics of hysteresis, it is suitable for low frequency applications. In addition, the woven fiber is not sensitive to the environment, the thermal stability is good, and the direct light / heat (such as the sun) has little influence on the environment. Therefore, it is especially suitable for automobile audio and outdoor applications.

5、Metal materials

Metal material is a kind of new type of cone diaphragm material which is rising in recent years. So far, the damping of the metal is the smallest, and the high frequency region of the peak is great, and the 6.5 inch speaker is also very common in the 5kHz 12dB. However, under the first segmentation vibration, the metal sound basin is very good, and this is the main point of its popularity.

The most common metal cone diaphragm is al (and its alloy) and magnesium. If it is possible to use a variety of forming and surface treatment technology for the processing of metal materials, the emergence of high performance metal cone diaphragm speakers is not difficult to imagine. However, even with the best frequency divider design, the high frequency section of the current metal basin is also very poor, so it is not much to choose the metal basin as a broadband system.

6、Other materials

Many speakers manufacturers are trying to find a better solution for a certain application (or a product that is just for larger market demand) by constantly changing basic materials and structures. All kinds of layered structure, paper composite, Kevlar, and plastic composite materials for the recent production, because it is the use of some new technologies, all of these materials in favor of or against the publicity must be very carefully considered.

Overview of cone material

Hope that this date, we have clearly used for high performance sound of the best cone diaphragm material depends on the actual needs, should be based on the need to compromise. In addition, you have to keep in mind is: the design of speakers, far more than the use of the cone diaphragm material. Diaphragm contour shape, material thickness distribution, folding ring and the centering support chip in different frequency characteristics, a voice coil size and material, the structure of magnetic path, and so on are on the speaker's final performance of the play great role. Dear reader, I mean you must not be able to judge the performance of a speaker by a single film material.