WO2009129815A1

WO2009129815A1 - Dual cone and multi cone assembly of a membrane

Info

Publication number: WO2009129815A1
Application number: PCT/DK2009/050095
Authority: WO
Inventors: Birger JØRGENSEN
Original assignee: Scan-Speak A/S
Priority date: 2008-04-23
Filing date: 2009-04-23
Publication date: 2009-10-29

Abstract

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, wherein the membrane comprises a first cone which first cone between the inner edge and the outer edge has one or more additional cones superposed the first cone, which additional cone(s) is/are glued to the first cone.

Description

Dual cone and multi cone assembly of a membrane

Field of 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 assembly of the cone-shaped type, but where the membrane assembly consists of two cones glued together with a damping glue for additional damping while spacing assures that the cone assembly remains stiff. Spacing between the two very thin cones is handled with a rib structure geometry in the cone itself for example as a reinforcement which is integral with the membrane in the shape of a deformation or bead of the membrane material or as an external piece of material fitted to the surface of the cone material.

Back ground of Invention

In a loudspeaker the mechanical properties of the membrane, also called 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 magnet system of the driver, which translates the electrical input from the sound generating equipment into movement of the membrane, need a higher force factor for higher mass load. At the same time the membrane material must have high stiffness in order to convert the force from the motor system into acceleration without excessive change in membrane geometry under load and hence without excessive distortion. Finally the damping properties of the membrane must ensure that vibration in the membrane is kept under sufficient control in a way that vibrations patterns in the membrane does not excessively influence the quality of the radiated sound and hereby the damping assist in keeping the distortion under control. Object of the Invention

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

Among these proposals are constructions known from US-A-2006018504 describing an advanced sandwich structure, requiring a complicated manufacturing process and a membrane structure which will have substantially homogeneous dampening characteristics in all directions, and a relatively expensive manufacturing process. Another example is suggested by DE 102004007020, wherein a gas filled membrane is disclosed. This structure, will obviously be relative fragile, prone to different dampening characteristics relative to the temperature, and thereby the pressure in the gas, and will during movement create gas pressure differences in the membrane which will distort the emitted sound.

It is therefore the aim of the present invention to alleviate these disadvantages by providing a membrane, which is both relatively stiff, light-weight and has a high degree of control over the vibration pattern from added damping, and at the same time obtain a wideband frequency response characteristic with the high stiffness in fiexural wave propagation.

Description of the Invention

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 that the membrane comprises a first cone which first cone between the inner edge and the outer edge has one or more additional cones superposed the first cone, which additional cone(s) is/are glued to the first cone, such that the glue between the cones maintains a controlled distance between each cone member in the assembly.

In this way way, the ribs separate the cones and form a more rigid structure while making room for damping material. The shape of the rib pattern is not critical. Some shapes may work better than others, but the separation of the cones with glue in between is the basis for the achieved effect. The ribs are pressed into or attached to one or both or all cones in order to force a gap between them. This creates an inherent rigidity. The glue used to hold the two cones together also adds damping to the system which is a further benefit.

Material options for the cone may typically be paper, but may also be textile (e.g. for textile dome tweeters), a polymer material (PP, PS, PE, PVC, whatever), fiber cones (typically glass, kevlar or carbon fiber), a metal (e.g aluminium, titanium, magnesium, beryllium - are currently used for loudspeakers), wood - like balsa wood.

Further advantageous embodiments of the invention are set out in the dependent claims.

One such embodiment disclose a membrane where one cone has an outer edge which is essentially cylindrical and which has an outer diameter larger than the cone behind it.

Description of the Drawing

Figure 1 Section A-A illustrates an implementation of two cones glued together; here termed "back" and "front" cone.

Figure 2 illustrates a perspective of a membrane according to the invention

Figure 3, illustrates a section of a multi layered membrane structure

Detailed Description of the Embodiment

In fig. 1 is illustrated a cut through a membrane according to the invention. Along the outer diameter (OD) 5, is fastened a surround 6, and along the inner diameter (ID) 7 is arranged a flange 8, suitable for attachment of a voice coil. The membrane 1 between the OD and ID is made from two superposed cones 2,3 (see fig 2).

In this particular embodiment, see fig 1 both cones have the rib structure (10,11) to keep the distance between the cones 2,3 constant, but only the rib structure 11 on the rear cone 3 plays an active role as keeping distance between the cones. The front cone rib structure 10 reinforces the stiffness, but is in contact with free air. In the implementation of fig. 1, both cones 2,3 have the same cone geometry, but they are cut on two different diameters. By the cone neck 8 (where the voice coil is attached) the front cone 2 is cut at a smaller ID than the rear cone 3. By the cone edge 5 (where the surround is attached) the front cone 2 is cut at a larger OD (outer diameter) than the rear cone 3.

In the particular embodiment of the front cone 2, it has a lip 12 that bends down and embraces the edge of the rear cone 3, keeping the glue between the two cones, preventing excessive glue from moving outward and into contact with the surround.

Given that a rib structure 10, 11 is implemented to add distance between the cones 2, 3, it is possible to make each cone embodiment as thin and light as possible. Bending stiffness will be achieved through the thickness of the assembly. The cones 2, 3 are made as light as possible while maintaining that each cone is fairly water proof (to have a stable coating process when applying the damping glue) and fairly air tight (for processing reasons at the manufacturer of the paper cone).

In the first implementation of this design, a 6.5" woofer/midrange, the front and rear cones have weights of 1.9 and 1.7 grams. The total assembly has a weight of approximately 5.5 grams. This is within typical range for a 6.5" woofer/midrange cone.

Turning to fig. 2 a membrane according to the invention is illustrated. On the membranes surface 13, the rib 10 of the upper most cone 2 is clearly visible. For illustrative purposes the space keeping rib 11 is illustrated with a thinner line. For most cone materials the rib 11 will not be visible on the surface 13. From the illustration it is evident that the ribs are off-set relative to each other, for example 60 degrees, when the ribs have a petal shape with three gloves.

In fig. 3 is illustrated a section through a membrane with a multi-cone structure in this illustrative example four cones 14 - 17. The space keeping ribs 11, 11 ', 11" are arranged such that the ribs are not superposed as this may cause "hot-spots" on the membrane. By off-setting the ribs, a more homogeneous construction, having more or less constant characteristics across the membrane is provided. In between the cones 14 - 17 a suitable glue 18 is arranged as explained above. It may be the same type of glue or different types. By using different types of glue, having different elastic properties it becomes possible to construct membranes with very different and specific properties. Any PVA based glue may advantageously be utilised in connection with the inventive principle.

In further embodiments of the invention it is foreseen to utilize more cones e.g. two or more cones, in the example referred to in fig 3, four cones are used where the cones are made from coarse textile (e.g. Glass, Kevlar or Carbon fibre). If the cones have relatively open weave (=coarse) arranged with the weave at 90 degrees, then two cones can be joined together - rotate one cone relative to the other with 45 degrees. A great advantage of this arrangement which to a certain degree is also present in the embodiment above is that a strong low-order vibration pattern is prevented. The current embodiment uses two cones with clover leaf pattern where one cone is rotated 60 degrees relative to the other, which means that the dominating (low-order) vibration pattern is reduced significantly.

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, characterized in that the membrane comprises a first cone which first cone between the inner edge and the outer edge has one or more additional cones superposed the first cone, which additional cone(s) is/are glued to the first cone.

2. Membrane according to claim 1 where the additional cone 2 which is glued to the first cone 1 is equipped with a rib structure formed out of the plane of the cone material in order to maintain a certain distance between the cones.

3. Membrane according to claim 1 or 2 where all cones have a rib structure and where the rib structure either has the same geometry for all or the rib structure can be different for each member of the cone assembly.

4. Membrane according to claim 1 or claim 2 where the cones have a dome shape

5. Membrane according to any preceding claim where members of the cone assembly have the same or different inner diameters and outer diameters.

6. Membrane according to claim 1 where one or more cones in the assembly has a reinforcement which is integral with the membrane in the shape of a deformation or bead of the membrane material.

7. Membrane according to claim 1 where one or more cones in the assembly has a reinforcement which is added as a separate structure between the membranes in the assembly.

8. Membrane according to any preceding claim where the rib structure is in the shape of a petal and where the rib structure is continuous around the cone or where the rib structure consists of a number of sections arranged around the cone.

9. Membrane according to any preceding claim wherein 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 of the membrane.

10. Membrane according to claim 1 wherein the thickness increases from 0.3 mm to 2.2 mm, more preferred from 0.35 mm to 1.5 mm and most preferred to 0.5 to 1 mm.