Loudspeaker membrane and method for manufacturing such a membrane

Abstract

The invention relates to a loudspeaker membrane having a sandwich structure, having a central web separating two layers of material based on high-rigidity threads impregnated with a polymer resin, characterized in that the central web is formed from a layer of material based on oriented natural fibers that are impregnated with a polymer resin.

Claims

1. Loudspeaker membrane with a sandwich structure, which comprises a central core separating two layers of materials made of high-rigidity yarn, impregnated with a polymerised resin, wherein the central core is formed of a material made of oriented natural fibres that are nearly parallel to each other and are impregnated with a polymer resin wherein the natural fibers are in the form of a unidirectional textile structure.

2. Membrane according to claim 1, wherein the outer layers comprise a textile made of high-rigidity yarn.

3. Membrane according to claim 1, wherein the high-rigidity yarn of the outer layers are made of a material selected from the group comprising glass, carbon and aramid, taken individually or in combination with each other.

4. Membrane according to claim 1, wherein the natural fibres are chosen from the group comprising flax, silk, hemp, ramie, coir, sisal, jute, bamboo and cotton, taken either individually or in combination with each other.

5. Membrane according to claim 1, wherein the resin impregnating the outer layers is of the thermosetting type.

6. Membrane according to claim 1, wherein the central core has a thickness that ranges from 0.3 to 3 millimeters.

7. Membrane according to claim 1, wherein the natural fibres are made of flax and wherein the outer layers are woven structures made of glass yarn.

8. A loudspeaker membrane sandwich structure comprising: two high-rigidity yarn layers of a loudspeaker membrane sandwich structure, both of said two high-rigidity yarn layers impregnated with a polymerised resin; a loudspeaker membrane sandwich structure central core of a substantially unidirectional oriented layer of natural fibres impregnated with a polymer resin, said central core disposed between and separating said two layers of materials made of high-rigidity yarn; and wherein a surface of at least one of said two high-rigidity yarn layers defines an outer surface of said loudspeaker membrane sandwich structure which directly contacts and moves a mass of air.

Description

A BRIEF DESCRIPTION OF THE FIGURES

(1) The manner in which the invention is implemented, as well as the resulting advantages, is made known in the description of the method of implementation given below, in support of the appended figures, in which:

(2) FIG. 1 is a schematic perspective view of a stack of different layers, shown partially cutaway, which help in creating the membrane that is compliant with the invention;

(3) FIG. 2 is a cross-sectional view of a stack of FIG. 1 after it has been shaped and before it is cut as per the contours of the future membrane.

METHODS OF EXECUTING THE INVENTION

(4) As previously explained, the membrane pursuant to the invention comprises a stack of several layers.

(5) As illustrated in FIG. 1, this stack (1) comprises a first layer (2) that is made up of a fabric, typically made of glass yarn, and therefore comprising a crosswise grain (3) and a lengthwise grain (4) that cross each other perpendicularly.

(6) For example, layer (2) of the glass yarn can have a mass of approximately 50 g/m.sup.2, and be formed of yarn with a density of approximately 11 tex.

(7) Of course, other materials such as carbon yarn or aramid yarn can be used, possibly even in combination with each other.

(8) This stack (1) also comprises a layer (6) that is made of natural fibres in the form of a unidirectional structure. In this case, the different yarns (7) are positioned parallel to each other. They can be kept in place next to each other by different methods, especially via a very fine crosswise grain (8) that has a negligible influence on the properties of the layer forming the core. The influence of the crosswise grain (8) is low, but it is still preferable that it be positioned at 90 with respect to the high count yarn (7) in order to obtain a more homogeneous deformation.

(9) For example, the yarn (7) of the core layer can be made of flax, in the form of braids or ribbons with a width of approximately one millimeter, forming a unidirectional layer with a mass of 150 to 400 g/m.sup.2. This kind of layer has a thickness of approximately 0.2 to 3 mm. Preferably, the ribbons are obtained using flax fibre, which, after being gathered in strands, is carded and combed in order to orient the fibres in the preferred direction. It has been observed that these operations help in obtaining a relatively homogeneous orientation of the fibres while still maintaining the relatively greater thickness of the ribbon, and in obtaining a greater resistance to stretching in the direction of the ribbon. As compared to the traditional processes of treating flax fibres, this method avoids, as far as possible, the drawing operations that have a tendency to break the basic fibres. Similarly, and contrary to the classic method of packaging the flax strands, this method avoids operations of twisting, which, while increasing the ribbon's resistance to stretching, also have the tendency to reduce the thickness of the ribbon.

(10) In the illustrated form, the yarn (7) of natural fibres is placed parallel to the yarn of the skins (2) that are made of glass yarn. In this configuration, a certain reduction has been observed in the coupling phenomena in the normal mode; this can be attributed to the relative irregularity of the geometry of the natural fibres as compared to the irregularity of the glass yarn forming the skin (2).

(11) However, in other configurations, it is possible to give the natural fibres a position that is staggered with respect to that of the yarn of the skins.

(12) This stack is completed by a second skin (10), which is similar (or even identical) to skin (2) and is located on the other side of the core layer (6).

(13) In practice, when manufacturing a membrane, it is possible to first create the stack of the different layers and then cut the zones to dimensions that are slightly larger than those of the developed area of a membrane. Each of the subunits thus created is then coated in a resin that impregnates the skins (2, 10) as well as the core layer (6). The entire unit is then shaped under a hot press that ensures the cross-linking of the resin (in the case of a thermosetting resin).

(14) After it is shaped, and as illustrated in FIG. 2, the stack takes the desired form, which is typically that of a truncated cone, as shown in the illustration. Typically, the thickness (t) of the membrane, mainly influenced by the core layer (6), ranges from a few tenths of a millimeter to a few millimeters. The unit is then cut to the contour (22) of the membrane, typically at the junction between the truncated cone-shaped portion (20) and the peripheral flat portions (21) that are to be removed.

(15) As already mentioned, it is also possible to manufacture the membrane pursuant to the invention by using pre-impregnated reinforcements. In this case, the excess resin present in the skins (2, 10) seeps into the core (6) during the pressurising stage.

(16) It follows from the above that the membrane according to the invention has multiple advantages, a few of which are: high rigidity due to a sandwich structure distancing the two outer skins; satisfactory damping due to the use of oriented natural fibres; a simple manufacturing process which allows the different layers to be assembled and shaped in one stage only; the use of natural materials.