GB2359440A

GB2359440A - Stiffening flange for a conical loudspeaker diaphragm

Info

Publication number: GB2359440A
Application number: GB0003758A
Authority: GB
Inventors: Keith Leaman; Nicholas Pocock; Simon Pettman
Original assignee: Goodmans Loudspeakers Ltd
Current assignee: Goodmans Loudspeakers Ltd
Priority date: 2000-02-17
Filing date: 2000-02-17
Publication date: 2001-08-22
Also published as: GB0003758D0

Abstract

A loudspeaker diaphragm 12 has a flange portion 24,34 on its outer periphery, the flange portion extending approximately normal to an adjacent portion of the diaphragm. The flange portion may be formed as an integral part of the diaphragm, and may extend either rearwardly or forwardly on the diaphragm. The presence of the flange portion increases stiffness of the diaphragm, and is of particular benefit in reducing non-axisymmetric-type modes (Bell modes) in diaphragms contoured as elliptical cones.

Description

2359440 CONICAL LOUDSPEAKER DIAPHRAGM is The invention relates to a

conical loudspeaker diaphragm, and more particularly, to a diaphragm having an outer edge constructed so as to provide improved stiffness and performance to the diaphragm.

The term conical diaphragm as used herein is not limited to a strict geometrical meaning, but includes any loudspeaker diaphragm which flares about an axis from a small (in use, driven) inner end to a large outer end.

The diaphragm may be round in axial cross-section, but need not always be so. Other shapes, eg. elliptical, are contemplated.

The acoustic performance of a loudspeaker diaphragm is dependent on the diaphragm being able to maintain radial and circumferential stiffness during use. If the outer edge of the diaphragm is weak, vibration of the diaphragm in the axisymmetric-type modes increases and sound quality is correspondingly reduced.

Paper loudspeaker diaphragms are known in which an outer end of the diaphragm is extended as a flat flange which deviates from the conical contour on the remainder of the diaphragm. In such construction, the outer end of the diaphragm extends generally perpendicular to the central axis of the diaphragm, and is fastened to a structural support member (referred to as a "surround") of the apparatus on which the diaphragm is mounted. The flat flange on the diaphragm has the advantage of reducing the non-axisymmetric-type resonant-frequency modes PBell modes") of waves travelling around the periphery - 2 of the diaphragm. In diaphragms that are contoured as elliptical cones, the equivalent modes (where a wave or waves appears to run around the periphery of the diaphragm) are more prevalent, and cause serious acoustic problems; in diaphragms that are contoured as circular cones, this presents less of a problem. However, the flat flange has the disadvantage for diaphragms contoured as either elliptical or circular cones that radial stiffness of the diaphragm is severely reduced; the outer edge of the diaphragm is weak, and vibration due to axi symmetric -type resonant - frequency modes increases.

An object of the preferred embodiments of the present invention is to improve stiffening of the outer edge of a loudspeaker diaphragm, especially but not only in the case of a diaphragm that is elliptical, and thus to improve the acoustic performance of such diaphragm. Besides severely reducing axi symmetric -type resonantfrequency modes that are seen as radially-travelling waves on the diaphragm, the stiffening eliminates or at least reduces (by raising their resonant frequency) nonaxisymmetric- type modes (Bell modes) that are seen as waves travelling around the periphery of the diaphragm.

The invention is a conical loudspeaker diaphragm in which a flange portion on an outer periphery of the diaphragm extends at a substantial angle to an adjacent portion of the diaphragm to increase the stiffness of the periphery of the diaphragm.

Preferably the flange portion of the diaphragm extends approximately normal to the adjacent portion of the diaphragm. The flange portion may be integral with, 3 - and extend either rearwardly or forwardly of, the adjacent portion of the diaphragm. The diaphragm may be contoured as either a circular cone or an elliptical cone.

Preferred features of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:Figure 1 is a sectional view of an outer end of a conventional diaphragm and connected support structure; Figure 2 is a sectional view of an outer end of a first embodiment of the diaphragm of the invention and connected support structure; and, Figure 3 is a sectional view of an outer end of a second embodiment of the diaphragm of the invention and connected support structure.

The conventional diaphragm 10 in Figure 1 has a body 12 symmetric around a central axis 13, and terminating in an integral cylindrical flat flange 14. The flat flange 14 is connected to a cylindrical outer end 16 of a struc- tural support member 18 (referred to as a "surround") of an apparatus in which the diaphragm 10 is mounted. As previously mentioned, this conventional diaphragm has a severely- reduced radial stiffness.

A first embodiment of the diaphragm of this inven- tion is illustrated in Figure 2. A diaphragm 20 has a conical body 22 that terminates in an integral annular flange 24 (referred to as a "return") that extends approximately normal to, and rearwardly of, an adjacent portion 26 of the conical body 22. The diaphragm 20 is connected to a surround 28 through an outer face of the 4 adjacent portion 26 of the conical body 22.

If a resonant-frequency mode should become associated with the return 24, that mode would be unlikely to have any detrimental effect on the acoustic performance of the diaphragm, since its position on the reverse side of the cone means that return 24 is unlikely to parti cipate in acoustic output. Although ellipticalcone diaphragms are the major beneficiary of this invention, the presence of a return as in Figure 2 also creates noticeable improvement in acoustical performance of circular-cone diaphragms.

A second embodiment of the diaphragm of this inven tion is illustrated in Figure 3. The diaphragm 30 has a conical body 32 that terminates in an integral annular flange 34 that extends approximately normal to, and forwardly of, an adjacent portion 36 of the conical body 32. The diaphragm 30 is connected to a surround 38 through an outer face of the adjacent portion 36 of the conical body 32. In this arrangement, one face of the flange 34 comes into contact with an inner face 40 of a semitoroidal portion 42 of surround 38.

With respect to circular-cone diaphragms, this invention is aimed at improving the performance of the acoustic output at the frequencies of the first (,break up,) mode of the diaphragm. By forcing the surround to move in a different way in the first mode, the mode is shifted up in frequency where, due to the nature of vibrating loudspeaker diaphragms, the movement is less and acoustic distortion is consequently diminished.

While the present invention has been described in its preferred embodiments, it is to be understood that the words which have been used are words of description rather than limitation, and that changes may be made to the invention without departing from its scope as defined 5 by the appended claims.

Each feature disclosed in this specification (which term includes the claims) and/or shown in the drawings may be incorporated in the invention independently of other disclosed and/or illustrated features.

The text of the abstract filed herewith is repeated here as part of the specification.

A loudspeaker diaphragm has a flange portion on its outer end, the flange portion extending approximately normal to an adjacent portion of the diaphragm. The flange portion may be formed as an integral part of the diaphragm, and may extend either rearwardly or forwardly on the diaphragm. The presence of the flange portion increases stiffness of the diaphragm, and is of particular benefit in reducing non- axi symmetric -type modes (Bell modes) in diaphragms contoured as elliptical cones.

6

Claims

CLAIMS: 1. A conical loudspeaker diaphragm in which a flange portion on an outer periphery of the diaphragm extends at a substantial angle to an adjacent portion of the diaphragm to increase stiffness of the periphery of the diaphragm. 2. A conical loudspeaker diaphragm as in claim 1, wherein the flange portion extends approximately normal to the adjacent portion of the diaphragm. 3. A loudspeaker diaphragm as in claim 1 or 2, wherein the flange portion of the diaphragm is integral with the adjacent portion. 4. A loudspeaker diaphragm as in any one of claims 1 to 3, wherein the flange portion of the diaphragm extends rearwardly of the adjacent portion. 5. A loudspeaker diaphragm as in any one of claims 1 to 3, wherein the flange portion of the diaphragm extends forwardly of the adjacent portion. 6. A loudspeaker diaphragm as in any one of claims 1 to 5, wherein the diaphragm is contoured as a circular cone. 7. A loudspeaker diaphragm as in any one of claims 1 to 5, wherein the diaphragm is contoured as an ellip- tical cone. 8. A loudspeaker diaphragm substantially as herein described with reference to and as shown in Figures 2 and 3. 4 e -R- Amendments to the claims have been filed as follows CLAIMS:

1. A loudspeaker diaphragm assembly comprising a conical loudspeaker diaphragm and a supporting surround connected to an outer periphery of the diaphragm, a flange portion on the outer periphery of the diaphragm extending at a substantial angle to an adjacent portion of the diaphragm to increase stiffness of the periphery of the diaphragm, the surround in section having an outer end and a central arched portion, the outer end of the surround being adapted to be connected to supporting structure for supporting the diaphragm assembly in use.

2. A loudspeaker diaphragm assembly as in claim 1, wherein the flange portion of the diaphragm extends approximately normal to the adjacent portion of the diaphragm.

3. A loudspeaker diaphragm assembly as in claim 1 or 2, wherein the flange portion of the diaphragm is integral with the adjacent portion.

4. A loudspeaker diaphragm assembly as in any one of claims 1 to 3, wherein the flange portion of the diaphragm extends rearwardly of the adjacent portion.

5. A loudspeaker diaphragm assembly as in any one of claims 1 to 3, wherein the flange portion of the diaphragm extends forwardly of the adjacent portion.

6. A loudspeaker diaphragm assembly as in any one of claims 1 to 5, wherein the diaphragm is a circular cone.

7. A loudspeaker diaphragm assembly as in any one of claims 1 to 5, wherein the diaphragm is an elliptical cone.

8. A loudspeaker diaphragm assembly as in any preceding claim, wherein the central arched portion of the surround is arched forwardly of the diaphragm.

9. A loudspeaker diaphragm assembly substantially as herein described with reference to and as shown in Figures 2 and 3.

b.