We know that in the speaker, the voice coil will generate strong vibration in the magnetic field after the audio signal is turned on. The voice coil is fixed on the cone. The vibration of the voice coil also drives the vibration of the cone. The cone vibration forces the air to vibrate. , thus making a sound. Therefore, the cone is an important part of the speaker, the sound basin is different in material, and the sound quality is also different.
Sound basin classification and characteristics
At present, the horn cones on the market can be roughly divided into the following categories:
1. Paper cone: The paper cone is easy to be integrated with other materials, so there are several kinds of plastic paper cones and compact paper cones. Although the paper cone has a low cost, its tone performance is good and its sensitivity is high. Therefore, the paper cone is the most widely used.
2, PP basin: Polypropylene basin with low distortion, good at showing a variety of music, high cost.
3, wool basin: the use of wool as a sound basin, with good flexibility, good at performance of light music.
4. Bulletproof cloth basin: The bulletproof cloth basin has a wide range of speaker frequency, suitable for music lovers who like strong bass. However, its cost is high and it is difficult to make.
5, ceramic basin: good at expressing vocals, classical music, fine sound, good dynamic performance.
6, metal basin: adding aluminum, magnesium and other metal elements, strong rigidity. The horn has a strong explosive power and is suitable for dynamic music.
Sound basin material analysis
Paper material
Paper materials are traditionally made of sound cones and are often mistaken for outdated technology and are not suitable for high performance speakers. Paper cones are easy to machine into a variety of shapes without the need for complex and expensive molds, and their mechanical properties are adjustable over a wide range of effective ranges. However, untreated paper cones are very sensitive to the environment (especially humidity). When the ambient humidity changes, the moisture in the paper will change, resulting in changes in parameters such as carcass mass and Young's modulus.
In addition, although it is possible to process a cone of sufficient rigidity to obtain an extended frequency response range, the internal loss of the paper itself is insufficient to obtain a smooth roll-off. Also, the deviation in paper production is large, which is not conducive to the consistency of batch products. A variety of surface treatment methods can be used to overcome the above two deficiencies, such as latex or PVA polyvinyl alcohol-based coating, impregnation. These coatings help isolate the cone from the surrounding environment while increasing transmission losses and, therefore, smoothing high frequency response.
Adding other fibers such as carbon fiber to the pulp to improve the characteristics of the cone (Note: The main purpose of the coating treatment of some paper cones is aesthetics, and some of the used materials may not affect the sound performance of the speaker). Inconsistent paper production will improve through strict process control and material selection. The same pulp, the internal structure is completely different due to the papermaking method, dehydration, drying method, etc., and the physical constant changes accordingly. The natural drop type and the forced absorption type of the papermaking method have different thicknesses and densities even if the mass of the carcass is the same, the thickness of the front method is large and the density is small, the Young's modulus is small, and the internal loss is increased; the latter tends to be opposite. The reason why pulp cones have been used for more than half a century is the rich variety of fibers and the freely controllable internal structure. Other plastic skins or foils have no freedom and only change shape. Although the surface of the paper material appears to be a low-tech material, the properly processed paper cone can achieve good bandwidth and smooth response at the same time, which is comparable to high-tech materials. Experts are constantly researching the formulation, processing and surface treatment methods of new paper cones. Don't be surprised, based on cheap, old-fashioned paper materials, the basin technology will have the latest breakthroughs and rejuvenation.
2. Polypropylene materials (also called PP, CD, etc.)
The material was developed by the BBC in 1976. Because of its strong internal damping, the properly designed polypropylene unit does not require any equalization to achieve a flat response in the work area with high efficiency. Polypropylene materials are probably the most common material for cone applications. Many of the cones claimed to be made of polypropylene are actually doped with organics and other fillers (eg carbon fiber and Kevlar). Fillers control costs and also change the mechanical properties of the material. The polypropylene cone is inherently well damped, so as long as the band requirements are not very wide, smooth response is no problem. 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 material of choice for many researchers to perform speaker FEA analysis. Polypropylene materials are not easy to bond, so they were not recognized at an early stage. Modern advanced adhesive technology (early 80s) has completely solved this problem.
Now, from the cheap stereo to the first-class aristocratic audio ProAC Response 3 and the Hales System 2 signature version of the various speakers use polypropylene units, the final quality of such units mainly depends on the shape of the cone and the polypropylene formula Add material. Advantages: If the design is correct, a flat response, low acoustic staining, and good impulse response can be obtained. The crossover can be simple, efficient, and the splitting vibration is slow. Quality products can achieve the same level of transparency as the best paper cones. Disadvantages: It is not that there will be no other problems with polypropylene materials. Although there are not a large number of papers published (at least I don't know), some people think that polypropylene units exhibit visibly viscous or viscous behavior (viscosity is a nonlinear phenomenon, which is a constant system parameter. It will be affected by the recent history of the system.) It is generally believed that hysteresis is caused by the viscoelastic creep of plastic materials. (Viscoelastic creep means that the plastic material will expand slowly under pressure. The process may be linear or possible. It is non-linear and depends on the loss in the material). One of my respected colleagues believes that hysteresis is caused by the entrance between the voice coil skeleton and the cone. He believes that the voice coil generates heat, which spreads through the voice coil bobbin and softens the plastic cone or the adhesive at the next. The degree of softening depends on the heat dissipated by the voice coil. Therefore, the resolution of the bass in many polypropylenes does not match well with the popular metal dome treble. Despite the actual or imaginary problems, polypropylene materials are popular in high performance speaker system applications due to their good high frequency response and consistent performance.
3. High strength woven fiber containing resin
Most carbon fiber, fiberglass and Kevlar cones are of this type. This type of cone is made of fiber woven fabric bonded to epoxy or similar resin. The fiber itself has a very high tensile strength, and the proper amount of resin is implanted, and the material hardness is quite large. Undoubtedly, the braided cone band has expanded. However, the smoothness of the frequency response is affected because the internal loss is very low. It has been suggested that the random orientation of the fibers facilitates suppression of the standing waves of the cone, thereby smoothing the frequency response. Based on experience, this method has little effect on high-frequency response. The speaker tested and the high-frequency response are not smooth. Even the best KEVLAR, carbon fiber has a high Q peak at least in the upper part of the work area, generally the most sensitive 3-5KHZ in the human ear. The same is true for other rigid units such as metal cones, which will result in fatigue for long periods of listening and compression of the sound field perspective (hidden effect).
Many speaker manufacturers have been trying to improve the basic structure of a simple woven fiber cone. A manufacturer uses a composite of two layers of Kevlar fiber sheets bonded to a resin sheet and small silicon spheres. Woven fiber cones are less likely to be sticky (folding and elastic waves, and even magnetic circuit systems may still be there, but this is another problem.) For broadband applications, woven fibers may not be the preferred material, but inherent The hard and non-hysteresis characteristics make it suitable for low frequency applications. In addition, woven fibers are not sensitive to the environment, have good thermal stability, and are less affected by direct light/heat (such as the sun). Therefore, it is especially suitable for car audio and outdoor audio applications.
4. Metal materials
Metallic materials are a recently emerging cone material. Among the materials discussed so far, the metal has the least damping, so the peak in the high frequency region is extremely large, and it is common for the 6.5-inch speaker to reach 12 dB at a peak of 5 kHz. However, the metal cone is very good under the first split vibration, which is the main point of its popularity. The most common metal voice coils are aluminum (and its alloys) and magnesium. The appearance of high-performance metal cone speakers is not unimaginable if it is possible to apply a variety of forming and surface treatment techniques to metal materials. However, even with the best crossover design, the current high frequency band of metal cones is not ideal and therefore not suitable for full-band system applications.
5. Other materials
Many speaker manufacturers are constantly experimenting with basic material and structural changes to find a better cone material solution for a given application (or just for a market with a promising product). Various layered structures, Kevlar and paper composites, Kevlar and plastic composites are recently made of such materials.
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