EP0082086A1 - Loudspeaker diaphragm and method for its manufacture - Google Patents

Abstract

The membrane can for example consist of an assembly of panels (1, 5) of continuous resistant fibres, for example carbon, impregnated with a polymerisable synthetic resin, the membrane consisting of two layers (2, 6) of panels extending in a radial or virtually radial direction of the membrane and the resistant fibres of the other layer of panels being directed in a direction perpendicular or approximately perpendicular to the generatrices of the membrane. The method consists essentially in cutting out from a sheet of unidirectional fibres, and in the desired orientation, panels (1, 5), and in arranging them on the core of a heating mould in order to ensure the polymerisation of the resin. <IMAGE>

Description

The present invention relates first of all to a loudspeaker membrane of the composite type, comprising a divided reinforcement material impregnated with a homogeneous material ensuring the continuity of the structure of the membrane.

In certain membranes of this type, said material is paper and is therefore only relatively homogeneous, and the divided reinforcement material consists of carbon rods; these are cut fibers at most 10 mm and which are scattered and glued into the dough, often without precise orientation. Carbon is thus very badly used, and the increase in weight and above all in cost price that its use entails is not optimally compensated for by an increase in the mechanical and acoustic qualities of the membrane, the homogeneity of which leaves elsewhere to be desired.

In other membranes, said material is polypropylene in which, to improve the rigidity, necessary especially at low frequencies, a powder has been incorporated, for example talc. We also know membranes made from the same kind of polymers, and including graphite in powder form, to densify the synthetic material and try to make it more rigid.

However, here again, the reinforcing material is very badly used and only allows very imperfectly to obtain the desired qualities for the membranes. In particular, such a powder material, as well as a rod material, practically does not make it possible to obtain a significant increase in the modulus of elasticity of the membrane.

The object of the present invention is to remedy these drawbacks of the prior art, with regard to said composite membranes.

For this purpose, a loudspeaker membrane of the general type specified at the start is, in accordance with the invention, characterized in that said material consists of a polymerized synthetic resin, and in that said reinforcing material consists of fibers resis continuous aunts.

The determining advantage of this basic arrangement lies in the fact that it will thus be possible to conveniently orient said continuous fibers in the direction or directions of the dominant stresses, and thus to avoid as much as possible the deformations of the membrane. We can therefore significantly increase the stiffness of the membrane in the directions in which the modulus of elasticity must be very high.

Thus, in particular, provision may be made for at least part of said continuous resistant fibers to be directed essentially in a radial or approximately radial direction of the membrane, which will make it possible to obtain a high elastic modulus in this radial direction, or else that at least part of said continuous resistant fibers are directed essentially in a direction perpendicular or approximately perpendicular to the generatrices of the membrane, which will make it possible to obtain a high elastic modulus in the circumferential direction.

Particularly advantageously, provision may be made for continuous resistant fibers directed, one in one of the two directions defined above, and the others in the other direction.

This can be conveniently obtained in a loudspeaker membrane which, according to another aspect of the invention, will be characterized in that it is produced in the form of a laminate, namely that it comprises at least one layer of continuous resistant fibers directed essentially in a radial or practically radial direction of the membrane, and at least one layer of continuous resistant fibers directed essentially in a direction perpendicular or approximately perpendicular to the generatrices of the membrane.

Of course, there may be more than two superimposed layers of one or the other type, and for example alternating, or even one or more layers in which the fibers will be. approximately 45 ° from directions above defined.

Whichever embodiment is envisaged, a fiber having a particularly high modulus of elasticity and, if possible, low density, will advantageously be used to obtain the above results. For this purpose, carbon fibers with a high modulus of elasticity, boron, kevlar, or glass (R or E) may be used for this purpose.

Carbon will be particularly advantageous, having a low density and a particularly high modulus of elasticity. These two properties are particularly valuable for the constitution of a loudspeaker membrane, because they will make it possible to obtain a sparse and extremely rigid membrane, implying a very high internal damping and an excellent yield. These qualities are particularly important for the passage of low frequencies.

In terms of practical implementation, a membrane according to the present invention may also be characterized in that it is produced from assembled panels, continuous resistant fibers pre-impregnated with a polymerizable synthetic resin.

This constitution in panels will allow easily to obtain, by juxtaposition, exactly the desired conformation of membrane, in the form of a truncated cone, portion of hyperboloide, ellipsoid, dome, or other more or less complex geometric shapes. , the number and shape of said panels being determined according to the different curvatures to be obtained and the desired direction for the fibers in each section.

In the most conventional case of a loudspeaker membrane in the shape of a truncated cone, the membrane may therefore be characterized in that said panels have the overall shape of truncated cone sectors.

The different panels can be juxtaposed exactly, without extra thickness, but it may be advantageous, on the contrary, to ensure that the radial edges of the panels of resistant fibers overlap one another to form narrow ribs, which preferably extend from one end to the other of the membrane.

A certain number of regularly stiffened radial ribs will thus be obtained. These ribs may have a width of 2 to 3 mm. This arrangement will further increase the elastic modulus of the membrane in exactly radial direction, and this with a negligible weight increase.

Similarly, provision may be made for the lower and upper edges of at least some of the resistant fiber panels to overlap one another to form one or more ribs or corrugations parallel to the periphery of the membrane.

This will give rise to the creation of ribs or corrugations similar to those encountered on conventional membranes, allowing additional stiffening in the direction perpendicular to the generatrices, as well as a reduction in the speed of propagation of sound in the material, between the point of attack and the peripheral attachment point.

In the case of a laminate membrane, provision may also be made for a honeycomb structure between two layers of continuous resistant fibers. This structure, which will be of the order of a few millimeters thick, may for example be made of aluminum or alternatively of cardboard impregnated with a phenolic compound, and will also make it possible to stiffen the membrane.

The impregnated cardboard can very easily be stuck on the layers of resistant prepreg fibers.

A membrane according to the present invention may also internally include a bonded veil and having a non-united surface, for example of non-woven material (glass or polyester fibers) fixed on a light support (40 g / m2).

This arrangement will attenuate the overvoltage of the resonances.

A decorative element, for example polyester, white or colored, could also be incorporated into a such a membrane and could serve as a shock absorber of resonances.

The invention further relates to a method of manufacturing a membrane including one or more of the arrangements which have just been listed.

When the membrane will be made up of panels, a process for manufacturing a membrane in accordance with the present invention may in particular be characterized in that said panels are cut from sheets of resistant unidirectional fibers, prepreg of a polymerizable synthetic resin.

Of course, the orientation of the cutouts in the sheet will be chosen according to their shape and the orientation that is desired for the continuous fibers of the membrane (radial or approximately radial, perpendicular or approximately perpendicular to the generatrices).

Preferably, the panel cuts are produced in sheets in which the synthetic resin represents at most 30 to 40% of the total volume of the resin and of the fibers, this in order to obtain the optimum tensile strength, said fibers preferably being in carbon. The prepreg is therefore relatively wrung out, but it still retains a relative tack, which will facilitate the positioning of the panels in the mold.

It is preferable to use plies of fibers having a thickness of the order of 125 u, which, with two layers of panels, will make it possible to obtain a membrane 1/4 mm thick, and a weight of the order 10 g for a diameter of 20 cm.

Thanks to this process, a very great homogeneity of the membrane will also be obtained, which will avoid distortions of sound, especially at high frequencies, when the loudspeaker operates mainly in radiation.

It has also been noted that a membrane according to the invention has a very low natural resonance.

A particularly advantageous mode of molding, for the implementation of a process in accordance with the present invention, may consist essentially in that the synthetic resin is polymerized in a heating mold comprising a male part or core of a shape complementary to the shape of the concave face of the membrane, said panels being placed on this core in the desired orientation and optionally in several layers, then from which one folds, on a base of said core, a crown capable of pressing between it and said base the edge of a waterproof sheet covering. said core coated with panels, a vacuum outlet provided on said base communicating with the space provided under said sheet.

We can thus save the female part of the mold, while obtaining sufficient pressure on the membrane during polymerization. In addition, the implementation of such a mold is very fast.

• - la figure 1 montre en perspective et schématiquement le positionnement d'une couche de panneaux en fibres résistantes continues préimprégnées par une matière synthétique polymérisable, par exemple une résine époxy, pour la constitution de tout ou partie d'une membrane de haut-parleur conforme à la présente invention ;
• - la figure la est une vue en plan d'une nappe de fibres unidirectionnelles préimprégnées, montrant les emplacements correspondants des découpes des panneaux ;
• - la figure 2 montre en perspective et schématiquement le positionnement d'une autre couche de panneaux en fibres résistantes continues préimprégnées par une matière synthétique polymérisable, par exemple une résine époxy, pour la constitution de tout ou partie d'une membrane de haut-parleur conforme à la présente invention ;
• - la figure 2a est une vue en plan d'une nappe de fibres unidirectionnelles préimprégnées, montrant les emplacements correspondants des découpes des panneaux ;
• - la figure 3 montre en perspective et schématiquement la superposition des couches des figures 1 et 2 pour la constitution d'une membrane de haut-parleur conforme à la présente invention, avec arrachement partiel ;
• - la figure 4 est une vue schématique de la membrane, vue en bout, et montrant une autre caractéristique de l'invention ; et
• -les figures 5 et 6 sont des vues schématiques, respectivement en perspective et en coupe axiale, d'un moule utilisable pour la mise en oeuvre d'un procédé conforme à un autre aspect de l'invention.

An embodiment of the invention will now be described by way of nonlimiting example, with reference to the figures of the appended drawing in which:

• - Figure 1 shows in perspective and schematically the positioning of a layer of continuous resistant fiber panels prepreg with a polymerizable synthetic material, for example an epoxy resin, for the constitution of all or part of a conforming loudspeaker membrane to the present invention;
• - Figure la is a plan view of a sheet of prepreg unidirectional fibers, showing the corresponding locations of the cutouts of the panels;
• - Figure 2 shows in perspective and schematically the positioning of another layer of panels made of continuous resistant fibers pre-impregnated with a polymerizable synthetic material, for example an epoxy resin, for the constitution of all or part of a loudspeaker membrane according to the present invention;
• - Figure 2a is a plan view of a sheet of prepreg unidirectional fibers, showing the corresponding locations of the cutouts of the panels;
• - Figure 3 shows in perspective and schematically the superposition of the layers of Figures 1 and 2 for the constitution of a loudspeaker membrane in accordance with the present invention, with partial cutaway;
• - Figure 4 is a schematic view of the membrane, seen at the end, and showing another characteristic of the invention; and
• FIGS. 5 and 6 are schematic views, respectively in perspective and in axial section, of a mold which can be used for implementing a method according to another aspect of the invention.

In Figure 1, there are referenced in 1 the panels, eight in number in this example, for the constitution of a membrane 2 according to the invention.

As can be seen, these are panels whose fibers extend from one end to the other of the membrane, namely radially or approximately radially. Continuous fibers, carbon for example, being originally all parallel since the panels are cut from a sheet 3 of unidirectional fibers (FIG. 1a), it goes without saying that only the central fibers of each panel are strictly radial.

As can also be seen in FIG. 1, two neighboring panels overlap slightly by their radial edges, so that there are obtained on the membrane eight radial stiffeners 4 with equal angular spacing (45 °), in the case where the panels 1 cut from the sheet of fibers 3 (or from several stacked sheets) all have the same dimensions.

FIG. 2 represents a membrane 6 (or a portion of membrane) formed with eight panels 5 of fibers cut from the ply (s) 3 (FIG. 2a), but being oriented at 90 ° relative to their orientation according to FIG. A membrane 6 is then obtained in which the resistant fibers extend in a direction perpendicular, or approximately perpendicular, to the radial directions. Again, it is possible to provide overlaps between the edges of the panels, in order to obtain radial stiffeners 7.

In the embodiment of FIG. 3, we have constituted a laminate membrane 2-6, by superimposing a membrane of the type of that of FIG. 1 with a membrane of the type of that of FIG. 2. By angularly positioning, in a suitable manner, the membrane 6 with respect to the membrane 2 , it is possible to ensure that the stiffeners 7 are regularly interposed between the stiffeners 4, the laminated membrane then having sixteen ribs or stiffeners with angular spacings of. 22.5 °.

It goes without saying that the membrane could consist of more than two superposed layers; as specified above, moreover, a honeycomb structure or the like could be interposed between two layers of panels. (We have not shown in the drawing all the additional provisions which have been mentioned in the foregoing in a sufficiently explicit manner).

One could also provide fiber panels oriented at ⁺ 45 ° or about relative to the previous ones. The panels would then be cut as shown in Figure 1a.

In FIG. 4, another way has been shown of slightly superimposing the lower edge of certain panels and the upper edge of the panels situated immediately below, this in order to obtain ribs or corrugations 8 parallel to the peripheral edge 9 of a membrane 10.

Such corrugations may be provided over the entire radial extent of the membrane, or only near its outer edge.

Of course, in this case, at least a portion of the panels will have a height significantly less than the radius of the membrane 10.

In Figures 5 and 6, there is shown schematically a molding process, according to the invention, for the preparation of membranes also according to the invention.

Plated on a conical core 11 provided with a base 12 different panels of resistant fiber impregnated genes 13 (in one or more layers). These panels are then capped by an optionally grooved counter-form 14, which may be made of sheet metal or of a slightly porous material, but which perfectly matches the external shape of all the panels 13 placed on the core. Next, a waterproof sheet 15 can be extended over the assembly, which can be flexible, or semi-rigid and preformed like the counterform 14, a sheet which is silicone-coated and which is reusable.

Finally, we close and lock on the base 12 a crown 16 connected to the base by a hinge, which allows to press in a sealed manner the edge of the sheet 15 on an O-ring 17 surrounding the core 11 and housed in a circular groove in the base 12. It then suffices to create a vacuum under the sheet 15, by a vacuum outlet 18 passing through the base, in communication with another peripheral groove 19, so that the counter-form 14 presses them panels 13 on the core 11 throughout the duration of the polymerization.

When the polymerization is complete, there is obtained, after cooling, an immediate release from the mold by simply opening the crown 16 and removing the sheet 15 and the counterform 14.

As goes without saying, and as it already follows from the above, the invention is in no way limited to those of its modes of application and embodiments which have been more particularly envisaged; on the contrary, it embraces all its variants.

In particular, and although, in the examples described above, consideration has been given above all to the production of membranes in the form of a truncated cone, the invention could be applied to the manufacture of membranes having many other forms, and for example a flared shape, the generatrices of the membrane no longer being straight lines, including in the case of a truncated cone, but curves.

One could also consider manufacturing, always on the basis of the same principles, faceted type membranes, that is to say whose intersection with a plane perpendicular to the axis would no longer have the shape of a circle, as in the case of a conical membrane, but the shape of a polygon.

In general, it is quite clear from the above that the invention will make it possible to produce all the forms of membrane currently known.

Claims (16)

1. Loudspeaker membrane of the composite type, comprising a divided reinforcement material impregnated with a homogeneous material ensuring the continuity of the structure of the membrane, characterized in that said material consists of a polymerized synthetic resin, and in that said reinforcing material consists of continuous resistant fibers. 2. Membrane according to claim 1, characterized in that at least part of said continuous resistant fibers are directed essentially in a radial or approximately radial direction of the membrane. 3. Membrane according to claim 1, characterized in that at least part of said continuous resistant fibers are directed essentially in a direction perpendicular or approximately perpendicular to the generatrices of the membrane. 4. Membrane according to any one of the preceding claims, characterized in that it is produced in the form of a laminate, namely that it comprises at least one layer (2) of continuous resistant fibers directed essentially in one direction radial or practically radial of the membrane, and at least one layer (6) of continuous resistant fibers directed essentially in a direction perpendicular or approximately perpendicular to the generatrices of the membrane. 5. Membrane according to any one of the preceding claims, characterized in that it comprises one or more layers of continuous resistant fibers extending under approximately - 45 ° relative to the radial directions of the membrane. 6. Membrane according to any one of the preceding claims, characterized in that said continuous resistant fibers constituting said reinforcing material are carbon fibers with high modulus of elasticity, boron, kevlar, or even glass (WHEEL) . 7. Membrane according to any one of the claims tions above, characterized in that it is produced from assembled panels (1,5), of continuous resistant fibers pre-impregnated with a polymerizable synthetic resin. 8. Membrane according to claim 7, generally in the form of a truncated cone, characterized in that said panels (1.5) have the overall shape of truncated cone sectors or the shape of trapezoids, planes or curves. 9. Membrane according to claim 7 or 8, characterized in that the radial edges of the resistant fiber panels overlap each other to form narrow ribs (4,7), which preferably extend from d from one end to the other of the membrane. 10. Membrane according to any one of claims 7 to 9, characterized in that the lower and upper edges of at least some of the resistant fiber panels overlap each other to constitute one or more ribs or corrugations ( 8) parallel to the periphery (9) of the membrane (10). 11. Membrane according to any one of claims 4 to 10, namely of the laminated type, characterized in that between two layers of continuous resistant fibers is interposed a honeycomb structure. 12. Membrane according to any one of the preceding claims, characterized in that it internally has a bonded veil and having a non-united surface. 13. A method of manufacturing a membrane according to any one of claims 7 to 12, characterized in that said panels (1,5,1 ') are cut from plies (3) of unidirectional resistant fibers, pre-impregnated with '' a polymerizable synthetic resin. 14. Method according to claim 13, characterized in that the panel cuts are produced in sheets (3) in which the synthetic resin represents at most 30 to 40% of the total volume of the resin and the fibers. 15. The method of claim 13 or 14, characterized in that one develops the panel cuts in sheets (3) of fibers, in particular carbon or materials with similar mechanical characteristics having a thickness of about 125 microns . 16. Method according to any one of claims 13 to 15, characterized in that one proceeds to the polymerization of the synthetic resin in a heating mold- comprising a male part or core (11) of shape complementary to the shape of the concave face of the membrane, said panels (13) being placed on this core in the desired orientation and possibly in several layers, after which it is folded, on a base (12) of said core, a crown (16) able to press between it and said base the edge of a waterproof sheet (15) covering said core (11) coated with panels (13), a vacuum outlet (18) provided on said base communicating with the space provided under said leaf.

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