WO2009080055A1

WO2009080055A1 - Asymmetric reinforcement of a membrane

Info

Publication number: WO2009080055A1
Application number: PCT/DK2008/050336
Authority: WO
Inventors: Søren Steen NIELSEN
Original assignee: Scan-Speak A/S
Priority date: 2007-12-20
Filing date: 2008-12-22
Publication date: 2009-07-02

Abstract

The invention provides a membrane for a loudspeaker, transducer or the like wherein the membrane is limited by an outer edge and an inner edge where between said edges the membrane material is present, and where the outer edge of the membrane is a polygon seen in a plane view and the inner edge is circular seen in a plane view and where between the inner edge and the outer edge an asymmetrically arranged reinforcement of the membrane is arranged. The asymmetrically arranged reinforcement strengthens the membrane both in the membrane's own plane and perpendicular to the membrane's plane. The first stiffening capabilities is important in that due to various inaccuracies in the membrane's construction, the membrane material or the manner in which the movement is imparted to the membrane, in certain cases creates a wave motion in the membrane surface not only propagating from the centre towards the edge, but also a sound wave pattern which may travel around the membrane between the inner and outer edge. By providing the reinforcement asymmetrically an effective dampening of this wave pattern is achieved both with respect to the waves that travel from the inner circle towards the outer edge of the membrane and fort he wave patterns which travel in any direction between the inner and outer edges.

Description

Asymmetric reinforcement of a membrane

Field of the Invention

The present invention relates to a membrane for a loudspeaker, transducer or the like. In particular the inventive membrane according to the invention aims at providing a membrane of the cone-shaped type, but where the membrane in itself is stiffer than ordinary membranes without adding substantial weight or otherwise interfere with the good characteristics of cone-shaped membranes.

Background of the Invention In a loudspeaker the mechanical properties of the membrane, also called a diaphragm, is an important factor in determining the sound quality resulting from the loudspeaker construction. In order to design a loudspeaker and in particular looking at the loudspeaker membrane, the material, from which the membrane is made, shall have a low weight, high stiffness and good dampening properties.

The low weight property is important in that the driver, i.e. the magnetic system which translates the electrical input from the sound generating equipment, into movement of the membrane and which driver therefore must be able to move the membrane as quickly as possible in response to the electrical input in the driver in order to reproduce the sound as true to nature as possible. Therefore, the lighter the membrane, the less mass the magnetic system has to accelerate and thereby the better the loudspeaker responds and the better the sound is reproduced. At the same time the low weight material needs to have a high stiffness in order for the influences applied to the membrane by the magnetic system, is not swallowed or absorbed in wavy patterns in the mem- brane material and finally the dampening properties of the material must be such that as the membrane accelerates due to the impact from the magnetic system, the acceleration and thereby the resulting movement of the membrane must be instantaneous so that all other movements in the membrane have been dampened at this time. Object of the Invention

In the art various constructions of the membrane has been suggested in order to provide these properties.

One such example is US2005/281433 wherein a loudspeaker membrane is suggested which is made from hybrid yarns including a matrix component where the matrix may include a number of materials such as e.g. polyamide, polyphenylene sulphide and poly- etheretherketone and where the yarn construction further is reinforced by introducing a second group of materials, e.g. carbon or para-aramid. This rather complicated compo- sition is in response to the requirements of low weight, high stiffness and good dampening, but is a rather complicated and also costly solution.

Usually, however, the membranes are made from cellulose materials and one example of prior art suggesting to reinforce a cellulose based membrane is disclosed in US 5256837, wherein folds are made in the cone surface in order to provide for a stiff cone construction. These folds, however, do not transmit the sound in a natural way and thus distort the membrane sections between the folds so that an unsatisfying sound reproduction pattern is achieved.

A further example of a membrane construction is illustrated in US 2006/0083402 wherein a membrane having a polygonal outer rim and a circular inner rim is disclosed. In order to distribute stresses a deflective line is provided approximately halfway between the inner and outer rims. The purpose of the deflective line is to divide the cones surface into smaller areas. Also it is sought to avoid conspicuous ridged lines, in order to maintain the elasticity of the membrane.

A still further example of a membrane is illustrated in US 5418337. This membrane is attached to a surround. The surround has a traditional bead along an outer periphery, where it will be attached to the chassis. Along the inner rim of the surround, various extensions are provided, which are suitable to be overlaid the membrane material (adhesively bonded to the membrane material). In this manner the surround due to its adhesive connection to the membrane will move and dampen the membrane, and in this manner provided added strength to the membrane. It is therefore an aim of the present invention to alleviate these disadvantages by providing a membrane which is both relatively stiff, light-weight and has wideband frequency response characteristics and at the same time high fiexural wave propagation velocity.

Description of the Invention

The invention consequently provides a membrane for a loudspeaker, transducer or the like wherein the membrane is limited by an outer edge and an inner edge where between said edges the membrane material is present, and where the outer edge of the membrane is a polygon seen in a plane view and the inner edge is circular seen in a plane view and where between the inner edge and the outer edge an asymmetrically arranged reinforcement of the membrane is arranged.

The asymmetrically arranged reinforcement strengthens the membrane both in the membrane's own plane and perpendicular to the membrane's plane. The first stiffening capabilities is important in that due to various inaccuracies in the membrane's construction, the membrane material or the manner in which the movement is imparted to the membrane, in certain cases creates a wave motion in the membrane surface not only propagating from the centre towards the edge, but also a sound wave pattern which may travel around the membrane between the inner and outer edge. By providing the reinforcement asymmetrically an effective dampening of this wave pattern is achieved both with respect to the waves that travel from the inner circle towards the outer edge of the membrane and for the wave patterns which travel in any direction between the inner and outer edges.

Within the context of the present invention the term polygon shall be understood as a closed geometrical shape having many sides, or being bound by connected points, straight lines and/or arcs. This means that circles, ovals, ellipses, arcs, curves, straight lines or other geometrical figures may by used and connected in order to create the polygon.

In a further advantageous embodiment the asymmetrically arranged reinforcement has a clover-like or flower shape, having an uneven number of petals evenly distributed on the membrane, where the number of petals may be chosen as three, five, seven or nine petals.

In this connection and within the scope of the present invention, "clover-like or flower shape" aims a describing the geometrical pattern as depicted in the appended figures.

The shape of the reinforcement is the result of a desire to create an even reinforcing effect radially as well as concentrically.

This particular shape adds a minimum of mass to the membrane and at the same time provides stiffness for the waves which may be generated as explained above. Extensive testing has indicated that by having an uneven number of petals, e.g. three, five, seven or nine, superior dampening characteristics in combination with relative stiffness of the membrane as such are achieved. It is in this context important to realize that the num- ber of petals is chosen according to the size of the membrane so that e.g. where small membranes suitable for sound reproduction in the high frequency interval only three petals are used, whereas for large membranes used in the lower frequency intervals may be used e.g. seven or nine.

In a further advantageous embodiment the reinforcement is integral with the membrane in the shape of a deformation or bead of the membrane material, shaped in the membrane material. During the casting of the membrane or shaping of the membrane in a traditional way it is possible to arrange in the membrane shaping mould a protrusion and corresponding cavity so that the reinforcement in the shape of a bead formed in the membrane material provides the stiffness and thereby the reinforcement.

Alternatively, in a further advantageous embodiment the reinforcement is attached to the membrane's surface and where the reinforcement may be made from any of the following materials: paper, cellulose fibre, cardboard, aluminium, polymers such as PE, PP, PVC.

By having the reinforcement as a separate member pre-shaped in the clover or petal shape as described above, it is possible to combine two materials so that e.g. the mate- rial of the membrane may be one type, and the reinforcement another type whereby the material characteristics may be chosen according to different criteria whereby a combination of advantageous characteristics of two different materials may be combined in order to provide advantages to the membranes such as light weight, improved stiffness and improved dampening capabilities.

In a still further advantageous embodiment of the invention the material thickness of the membrane increases from the inner edge towards the outer edge.

The membrane in a loudspeaker construction is usually fastened to a so-called surround which surround again is fastened to the chassis, i.e. the carrying structure of the entire loudspeaker construction. The surround may have a material thickness which is thicker than the membrane material and is made from a different material as well, and by increasing the material thickness in the membrane it is possible to design the transition from the membrane material to the surround so that detrimental effects relating to the sound generation in the membrane may be minimized due to the transition between the membrane and the surround.

The reinforcement is continuous around the clover-shape in a further advantageous embodiment. It is contemplated that the reinforcement may be discontinued, so that sections of reinforcements may be added but in this further advantageous embodiment the reinforcement is continuous whereby in particular in order to alleviate undesirable waves in the membrane circling the membrane, this has proved to be an effective way to dampen these waves. Furthermore, by having a continuous reinforcement the likeli- hood of generating hotspots, i.e. points on the membrane where particularly high loads are generated due to material characteristics differences, resonance and the like are minimized.

In a further advantageous embodiment the invention the reinforcement, and thereby each petal is defined by a half circle adjacent the outer edge of the membrane, where each end of the half circle connects to the adjacent petal by a curve shape having a curvature opposite the half circle, and where optionally the half circle and the curve shaped sections may be connected by linear sections. In a further embodiment of the invention the reinforcement is discontinuous, such that the reinforcement is a plurality of U-shaped reinforcements, where the opening in the U is either open towards the inner or outer periphery or alternating between inner and outer periphery.

In a still further advantageous embodiment the outer edge of the membrane has a number of sections where each section has alternating linear sub-sections and circular sub- sections, and that there are three to eleven, more preferred four to eight, and even more preferred five to seven sections of even size distributed along the circumference o f the membrane .

The advantages of a membrane having cut or straight edge sections, but without the reinforcement according to the present invention, are already disclosed in the same applicant's prior patent application WO 9510165. By additionally adding the reinforcement according to the present invention a symbiosis between the two inventions provides for a greatly improved membrane construction.

In this embodiment the reinforcement is arranged asymmetrically with respect to the straight section and the circular sections of the outer edge.

Where the membrane in particular is made from a cellulose material, the invention in a further advantageous embodiment relating to the increase in thickness of the membrane from the inner edge towards the outer edge where the thickness increases from 0,3 mm to 2,2 mm, more preferred from 0,35 to 1,5 mm and most preferred from 0,5 mm to 1 mm. For these thin sections the reinforcement is a determining factor in providing the stiffness so that an overall improved, stiff and very light weight membrane is provided.

Also the reinforcement has a varying thickness, such that for example sections of the reinforcement being closer to the inner edge is thinner (and thereby also lighter) whereas sections further away from the inner edge may be thicker and thereby also stronger. Description of the Drawing

The invention will now be explained with reference to the accompanying drawing, wherein

Fig. 1 illustrates a plane view of a membrane according to the invention

Fig. 2 illustrates a cross section through a membrane as illustrated in figure 1 Fig. 3 illustrates an exploded view of a loudspeaker construction including a membrane according to the invention

Fig. 4 illustrates the loudspeaker construction according to figure 3 seen from above. Fig 5 illustrates a cross section through the membrane showing the reinforcement bead.

Fig 6 illustrates a cross section through the membrane illustrating a second embodiment of the reinforcement bead. Fig 7 illustrates a plane view of the membrane in an alternative embodiment.

Detailed Description of an Embodiment

In figure 1 is illustrated a membrane 1 according to the invention. The membrane is characterized by an inner edge 2 having a substantially circular shape and an outer edge 3 which in preferred embodiments has a polygon shape. The polygon shape indicates that the outer edge is made from a number of sections 3', 3". In figure 1 is illustrated as an outer edge including straight sections 3' alternating with round sections 3" so that five of these alternating sections are arranged around the outer edge of the membrane 1.

Arranged on or in the membrane's surface 4 is a continuous reinforcement 5. The rein- forcement is in the shape of a three petal 6 clover where the petals 6 are asymmetrically arranged in relation to the sections 3', 3". This is done in order to avoid any kind of symmetry in the membrane construction which could in case of the membrane hitting its natural frequency enforce this and thereby be detrimental to the proper reproduction of the emitted sound.

In figure 2 is illustrated a cross section through the membrane according to figure 1 along the line A-A. The sections 3', 3", constitute the upper edge of the membrane, and the circular inner edge 2 seen at the bottom of figure 2. On the membrane surface 4 the reinforcement 5 is illustrated. In this embodiment the reinforcement 5 is an integral part of the membrane material 4 which will be described in detail with reference to figure 5.

Turning to figure 3 an exploded view of the membrane construction for a loudspeaker unit is illustrated. A typical loudspeaker comprises a chassis 7, a surround 8, which surround 8 connects the chassis to the membrane 1. Typically a surround is a very flexible ring member. At the inner edge 2 of the membrane 1 a coil 9 is usually attached which coil is arranged in an air gap in a magnetic driver which due to a change of the magnetic field will make the coil move up and down whereby due to its connections to the membrane, the membrane will move up and down very rapidly and emit the sound. In order to guide the coil in the air gap, usually a spider 10 or other centering construction is arranged in connection with the coil 9.

In figure 4 a picture of a loudspeaker assembled as illustrated in figure 3 is as it will be seen to a user. The membrane 1 including the reinforcement 5 is clearly seen and in the centre of the loudspeaker, i.e. delimited by the inner edge 2 of the membrane, the driving magnet construction 11 may be seen. In most loudspeaker constructions a dust cover will be covering the opening limited by the inner edge 2 of the membrane in order to avoid foreign objects and in particular dust to be tangled up in the coil and air gap construction and thereby reducing the capabilities of the loudspeaker. Connecting the chassis 7 to the membrane is the surround 8 as already explained above.

Turning back to the particular construction of the reinforcement of the membrane as depicted in figure 5 the reinforcement 5 may be an integral part of the membrane material 4. In this embodiment it is also clearly seen that the material thickness of the membrane material 4 increases from the inner edge towards the outer edge. In the embodiment illustrated in figure 2 the material thickness at the inner edge 2 is approximately 0.55 mm and the material thickness at the outer edge 3 is approx 0.8 mm. The reinforcement clover-like structure in the shape of the bead 5 may have an added thickness or may have the same material thickness. In figure 5 is depicted a bead with an in- creased thickness which thereby also provides for an added geometric stiffness and reinforcement of the membrane.

In figure 6 is depicted a membrane material 4 onto which a reinforcement 12 is sup- plied. The reinforcement 12 may be applied by gluing, welding or any other type of adhesive. One advantage of the embodiment depicted in figure 6 is the fact that the membrane material 4 may be different from the reinforcement material 12 so that the different material characteristics may be selected so that the reinforcement may be made from one material having particularly good reinforcement characteristics for the specific purpose and the membrane may be selected from a material providing the membrane as such with particularly good characteristics, whereby the combination will provide a superior membrane construction altogether.

In fig. 7 is illustrated a plane view of another embodiment. The reinforcement 5' is in the shape of three U-shaped sections, arranged with the open end of the U towards the inner periphery/edge 2, of the membrane. It is evident that any number of reinforcement sections may be arranged, depending on the design and use of the membrane. Furthermore the reinforcement may be arranged with the open end of the U towards the outer periphery/edge 3, or a mixture, i.e some reinforcement sections 5' having their open ends one way and other sections 5 ' having the open ends the opposite way.

It is contemplated that the membrane may be of any type such as flat, cone-shaped and the like.

Claims

1. Membrane for a loudspeaker, transducer or the like wherein the membrane is limited by an outer edge and an inner edge where between said edges the membrane material is present, and where the outer edge of the membrane is a polygon seen in a plane view and the inner edge is circular seen in a plane view, characterised in that between the inner edge and the outer edge an asymmetrically arranged reinforcement of the membrane is arranged.

2. Membrane according to claim 1 wherein the asymmetrically arranged reinforcement has a clover-like shape, having an uneven number of petals evenly distributed on the membrane, where the number of petals may be chosen as three, five, seven or nine petals.

3. Membrane according to claim 1 wherein the reinforcement is integral with the membrane in the shape of a deformation or bead of the membrane material.

4. Membrane according to claim 1 wherein the reinforcement is attached to the membranes surface, and where the reinforcement may be made from any of the follow- ing materials: paper, cellulose fibre, cardboard, aluminium, polymers such as PE,

PP, PVC

5. Membrane according to claim 1 wherein the material thickness of the membrane increases from the inner edge towards the outer edge.

6. Membrane according to claim 1 wherein the reinforcement is continuous around the clover shape.

7. Membrane according to claim 1 or 6 wherein each petal is defined by a half circle adjacent the outer edge of the membrane, where each end of the half circle connects to the adjacent petal by a curve shape having a curvature opposite the half circle, and where optionally the half circle and the curve shaped sections may be connected by linear sections.

8. Membrane according to claim 1 wherein the reinforcement is discontinuous, such that the reinforcement is a plurality of U-shaped reinforcements, where the opening in the U is either open towards the inner or outer periphery or alternating between inner and outer periphery.

9. Membrane according to any preceding claim wherein the outer edge of the mem- brane has a number of sections where each section has alternating linear subsections and circular sub-sections, and that there are three to eleven, more preferred four to eight, and even more preferred five to seven sections of even size distributed along the circumference of the membrane.

10. Membrane according to claim 5 wherein the thickness increases from 0,3 mm to

2,2 mm, more preferred from 0,35 to 1,5 mm and most preferred from 0,5 mm to 1 mm.

11. Membrane according to any of claims 1 to 9 wherein the membrane has a cone shape.