Acoustics – Diaphragm – Critically defined material or coating
Reexamination Certificate
1999-10-29
2002-05-21
Nappi, Robert E. (Department: 2837)
Acoustics
Diaphragm
Critically defined material or coating
C181S167000, C181S166000
Reexamination Certificate
active
06390232
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to speaker cones and cone assemblies, and more particularly to a speaker cone comprising a composite material and to a cone assembly comprising the cone bonded to a surround, and to methods of making the same.
BACKGROUND OF THE INVENTION
Loudspeaker diaphragms are used to convert electric vibrations into mechanical vibration; the most common type is a cone assembly which generates acoustic sound by mechanical vibration of the cone. A cone assembly generally comprises a cone and a suspension member. The cone is a sound radiating cone which generally has a frustoconical configuration with a concave curvilinear profile. A cone is generally circular in shape, with a circular outer peripheral edge and a circular annular neck which may extend in the axial direction of the cone. This neck is at the center of the cone, and is referred to as a “voice coil inside diameter,” or VCID; it is open, and may be attached to a voice coil or the like in a conventional manner. The cone is adapted to be supported on a support frame through an annular suspension member or rim, which is secured to the outer marginal edge of the cone and which has predetermined elastic or flexibility properties. Such a suspension member may also be referred to as a roll edge or as a surround. The surround may be formed as an integral generally radially directed extension of the outer marginal edge of the cone, or it may be formed as a separate annular supporting flange or rim which is then affixed to the outer marginal edge of the cone.
Various materials have been used in the construction of loudspeaker cones, including metal, woven fabric, films of plastic, and pulp comprised of natural fibers or synthetic fibers, such as carbon fibers, glass fibers, and kevlar or acrylic. Two commonly used materials are paper pulp and plastic. Paper cones are generally prepared by forming cellulose fibers of paper to a certain configuration using a mold. Such cones are also referred to as fibrous or felted paper-type cones. Plastic cones are generally prepared by one of two ways; one way is shaping pellets of plastic resin into a film, and then vacuum molding the film to form a cone, and the other way is by directly injection molding the resin form into a cone shape.
Many properties of a speaker cone depend upon the material from which the cone is constructed. Such properties include the acoustic properties, the durability of the cone, the change in the acoustic properties of the cone over time, and the ability of the cone to withstand environmental conditions such as high and low temperature, moisture and ultra violet light. The cost of manufacturing speaker cones also depends upon the cone material.
Paper cones offer several advantages over plastic cones. Typically a paper cone has a wider acoustic range, as it has more varied capabilities and greater flexibility during its manufacture in terms of controlling its stiffness. Thus, a paper cone may be made harder or softer, such as by pressing or by chemical treatments; this flexibility of manufacture does not exist with plastic, as the same treatments have no effect on plastic cones. The performance of a paper cone is also superior to that of a plastic cone, where performance is defined as how much sound level is obtained per watt of power driving the speaker; this is because paper cones are generally stiffer at lighter weights than plastic ones, and the lighter the speaker, the less power it takes to drive it. In addition, the frequency range of a paper cone is much greater for a single paper cone than for a plastic polymer cone of similar dimensions. Thus, in instances where a single paper cone in a speaker assembly might suffice, it would take two or more plastic cones to match the sound range of the single paper cone.
The advantages of plastic cones include increased versatility in appearance; such versatility exists in the greater differences in color, surface sheen, and shapes which can be obtained with plastic cones. Furthermore, the sound quality of plastic cones tends to be more uniform in different environments and over time, as the cellulose material of a paper cone is strongly influenced by humidity. However, the performance of plastic cones is typically more influenced by temperature than is the performance of paper cones.
The material of a speaker cone also influences the type of surround which can be used with it. The relatively high amplitude vibrations in the axial direction of the speaker cone, to which dynamic or moving coil-type loudspeaker cones used for mid low frequency ranges are subjected, dictates that the surround be both flexible and durable. In the past, surrounds were made from rubber; however, rubber surrounds are generally expensive. Less expensive surrounds have been made from cloth, from a thermoplastic elastomer or from polyurethane foam material. These surrounds have been pre-fabricated and then attached to the outer marginal edge of a cone with adhesives. However, such surrounds have several drawbacks. One is that the selection of starting materials is limited. Another is that fabrication of such surrounds generally involves stamping or cutting out the surround form from sheets of material, resulting in considerable waste of starting material. Yet another is that such surrounds must be attached to speaker cones, usually by means of an adhesive; however, the choice of effective adhesives is limited, and even with the better adhesives, the resulting bonds between the surrounds and the cone are often less than optimal. Furthermore, the glue adds weight to the cone. Additionally, there may be considerable variation in the alignment between the surround and the cone, which may affect acoustic properties of the cone. Finally, fabrication and attachment of such surrounds require skilled hand assembly, and thus additional time and expense of manufacture.
Alternatively, polymer based surrounds have been molded onto speaker cones. By over molding it is meant that the surround is formed and attached to a cone in a single molding process, in which the outer peripheral edge of the cone is exposed to the polymeric surround material during the molding procedure. Different types of surrounds have been used in different molding procedures with different types of cones.
In one type of molded surrounds, foam surrounds have been fabricated and attached to a felted paper-type cone by molding the surround to the cone, as disclosed in U.S. Pat. No. 5,319,718. Such surrounds are prepared by a low pressure casting process, where a liquid polyurethane foam is placed in an open mold in contact with the outer marginal edge of the cone; the mold is then closed, and the foam is expanded and cured. The result is a cone assembly with a foam surround which is molded onto the outer marginal edge of the cone, where the surround forms a mechanical bond with the cone as a result of impregnation of the surround material into the fibrous material of the cone.
In yet another type of molded surrounds, an elastomeric surround can be injection-molded onto an injection molded cone, as is disclosed in EPO 552040 B1. In this case, the surround is formed by injecting an elastomeric material into a closed mold which also contains the cone; the outer peripheral edge of the cone comes into contact with the elastomeric material. The result is a cone assembly with an elastomeric surround molded onto the outer marginal edge of the cone. As disclosed by EPO 552040 B1, the cone is also formed by injection molding, and preferably the material of the cone and of the sourround are selected such that when the surround is injection molded onto the cone, the cone and the surround are chemically bonded to each other. By chemically bonded it is meant that the two become attached at a molecular level, due to cross-linking of the respective materials.
Attempts have been made to assemble paper cones with molded polymeric surrounds. However, several problems were encountered. One problem is poor attachment of an elastomeric surround with a paper c
Communications Products Corporation
Lockett Kim
Nappi Robert E.
LandOfFree
Speaker cone assembly does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Speaker cone assembly, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Speaker cone assembly will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2834889