GB2035008A

GB2035008A - Diaphragm suspension construction

Info

Publication number: GB2035008A
Application number: GB7918006A
Authority: GB
Original assignee: James B Lansing Sound Inc
Current assignee: Harman Professional Inc
Priority date: 1978-11-14
Filing date: 1979-05-23
Publication date: 1980-06-11
Also published as: BE879985A; NL188882C; NL7904338A; GB2035008B; DE2944445A1; JPS644400B2; FR2441979A1; JPS5567297A; FR2441979B1

Abstract

An annular suspension 20 for supporting an acoustic diaphragm 21 around its edge to permit axial diaphragm movement is made of thin folded sheet material such as aluminium and includes inner and outer concentric circular fold lines 40, 41 having a series of pyramid-like structures 30, 32 therebetween, each such structure extending no more than about 15 DEG of arc and having an approximately trapezoidal base defined by a first pair of opposed sides lying along said circular fold lines 40, 41 and by a second pair of opposed sides lying along fold lines which lie in planes extending radially of the suspension axis. A third circular concentric fold line is formed intermediate the inner and outer circular fold lines. The suspension 20 may be formed integrally with the diaphragm 21 which may be of the dome or cone configuration and is provided with a conventional voice coil. The suspension permits axial diaphragm movement by slight flexing at the fold lines, minimizing stretching of the sheet material and preventing torsional movement of the diaphragm. When the suspension is at rest, the inner and outer circular fold lines 40, 41 desirably lie in a common plane normal to the diaphragm axis; during operation the circular fold line adjacent to the diaphragm moves slightly from that plane, and the pyramid-like structures flatten slightly. <IMAGE>

Description

SPECIFICATION Diagram suspension construction This invention relates generally to the mounting of acoustic diaphragms in loudspeakers or the like, and more particularly to an annular suspension for supporting the outer and/or inner edge portion of an acoustic diaphragm and permitting axial but not torsional movement of the diaphragm relative to a fixed support frame to which the suspension is attached.

Prior suspensions, sometimes referred to as com pliances orsurrounds, have been proposed for supporting acoustic diaphragms, exemplified by the constructions shown in U.S. Patents 1,829,355 to Houghton and 3,563,337 to Kawamura. The principal objectives of such constructions, as well as of the present invention, are to prevent torsional or radial movement of the diaphragm while permitting axial movement thereof, and to minimize stress of the material of which the suspension is made, whereby to provide for long life of the suspension and to avoid distortion by permitting the diaphragm to move as nearly as possible in accurate response to the signal in the voice coil.

According to the present invention there is provided a suspension for supporting an edge of an acoustic diaphragm with respect to a fixed supporting member, comprising an annulus of thin sheet material including inner and outer concentric fold lines, a series of substantially pyramid-like structures, each structure having an approximately trapezoidal base defined by a first pair of opposed sides formed by portions of said concentric fold lines and a second pair of opposed sides formed as fold lines which lie in planes extending radially of the annulus axis and a third fold line concentric with and between said inner and outerfold lines. Preferably, each of the structures extends over no more than about 15 of arc, so that there are at least 24 of the structures.

The suspension can be formed integrally with the diaphragm it is to support for example of sheet aluminium or impregnated fabric material.

Axial excursion of the diaphragm in response to the voice coil signal causes flexing of the fold lines of the suspension, as distinguished from stretching of the suspension material itself.

A better understanding of the invention will be had from the following detailed description, given by way of example with reference to the accompanying drawings, in which: Figure 1 is a rear view of a diaphragm assembly including a suspension embodying the present invention and in which each pyramid-like structure extends 10 of the arc; Figure 2 is a side elevational view taken on arrows ll-ll of Figure 1; Figure 3 is a fragmentary front view taken on arrows Ill-Ill of Figure 2; Figure 4 is a fragmentary view on a greatly enlarged scale, taken on arrows IV-IV of Figure 1; Figure 5 is a fragmentary view on an enlarged scale looking forwardly on arrows V-V of Figure 4.

Figures 6,7 and 8 are sectional views taken respectively along lines VI-VI, VII-VII and VIII-VIII of Figure 5; and Figure 9 is a fragmentary view of a suspension in accordance with the invention, on which each pyramid-like structure extends only 5 of arc.

Referring in detail to Figures 1 and 2, a hollow annular frame of rigid material, typically dielectric, is indicated generally at 10 and is provided with a set of mounting holes 12, for example eight in number as shown, arcuately spaced about the frame. The diaphragm and its suspension are formed integrally of thin sheet aluminium, the dome diaphragm being indicated generally at 18 and the annular suspension being indicated generally at 20. The dome itself is specifically indicated at 21. Radially inwardly of the suspension is a conventional voice coil assembly indicated generally at 22 fixed to the diaphragm, including a bobbin 23 and the voice coil proper 24, connected to terminals 25 and 26.Radially outwardly of suspension 20 and formed integrally therewith is an annular skirt portion 28, best seen in Figure 4, by which the diaphragm and its suspension are fixedly attached to frame 10 by suitable adhesives and clamping rings well known in the art. It will be understood that all the constructions and elements thus far identified, except suspension 20, are conventional and well known in the loudspeaker art.

As best seen in Figure 1, suspension 20 is formed to provide a series of identical structures extending circumferentially about the periphery of dome 21.

Each of the structures is pyramid-like in configuration. As shown there are 36 such structures and each therefore extends through 10 of arc. For reasons later appearing, it is preferred that the arcuate extent of each modular structure not exceed about 15".

In suspension 20, two adjacent structures 30 and 32 will be described in detail, keeping in mind that Figures 1 and 5 look forwardly, while Figure 3 looks rearwardly.

It will be seen that the bases of structures 30 and 32 are apprnximatelytrapezoidal in shape, being bounded inwardly and outwardly by arcs of circular fold lines 40 and 41 respectively, and bounded laterally by fold lines which lie in planes extending radially of the diaphragm. Each lateral boundary is made up of two line segments which, as seen in section in Figure 8, are angularly related. More specifically, the lateral fold line seen in Figure 8 includes segments 44 and 45, which are inclined forwardly from inner and outer circular fold lines 40 and 41 respectively. Segments 44 and 45 meet at a point 46 which lies on a circular fold line 48 disposed intermediate the inner and outer circular fold lines 40 and 41.

With reference to Figures 5 and 7, pyramid-like structure 30 includes triangular faces 50 and 52, the apexes of the faces meeting at a common point 54 lying on intermediate fold line 48; in Figure 6, the lateral faces of structure 32 are approximately bisected by fold line 48, forming facets 56, 57 and 58, 59 which create slightly concave dihedral angles along line 48.

With the parts at rest, the inner and outer circular fold lines 40,41 lie in a common plane perpendicular to the diaphragm axis, as clearly appears in the drawings, particularly Figures 4,7 and 8. A signal applied to the voice coil 24 will cause the inner circu larfold line 40 to move leftwardlyand rightwardlyas seen in those Figures, and this movement is accommodated by slight flexing of the several fold lines, and with minimum stretching of the sheet material of which the suspension is made. The pyramid-like structures flatten slightly as the fold line 40 moves.

The bases of the pyramids are of course not true trapezoids in the geometric sense, but they approach that shape as the arcuate extent of each module is decreased, so that the arc approaches closer to a chord lying in a straight line, to facilitate the flexing or bending along the fold lines during operation. An arcuate extent of more than about 15 would unduly inhibit that bending. The form of the invention so far described includes 36 modules, each of 10" of an arc.

In Figure 9 is shown a fragmentary portion of a suspension in accordance with the invention having 72 modules, each extending 5" of arc, certain structural features being indicated by reference numerals 100 greater than corresponding features in Figure 5.

The geometric configurations of the present suspension facilitate diaphragm movement in the axial direction while providing enhanced stiffness in other directions, thus minimizing the possibility of partial or full cancellation occurring withinthe portion of the spectrum of interest.

The suspension of the present invention is described as having the general shape of an annulus. However, it is to be understood that the annulus and its derivatives are used herein to include a border extending along a margin or edge of a diaphragm of any usable shape, not limited to circular, but including ellipsoidal, polygonal, and combinations of such shapes.

The present suspension may be formed integrally with the diaphragm and the outer skirt, as shown and described herein, or it may be made as a separate annular element and attached to a diaphragm and skirt by suitable means or adhesives. It may be made of impregnated cloth, paper or fibreglass, or of other formable material such as suitable thermosetting or thermoplastic compositions. Other modifications are also within the contemplation of the invention, and are intended to be embraced within the scope of the following claims.

Claims

1. A suspension for supporting an edge of an acoustic diaphragm with respect to a fixed supporting member, comprising an annulus of thin sheet material including inner and outer concentric fold lines, a series of substantially pyramid-like structures, each structure having an approximately trapezoidal base defined by a first pair of opposed sides formed by portions of said concentric fold lines and a second pair of opposed sides formed as fold lines which lie in planes extending radially of the annulus axis, and a third fold line concentric with and between said inner and outer fold lines.

2. A suspension as defined in claim 1, wherein the suspension is formed integrally with the diap hragm it is to support.

3. A suspension as defined in claim 1 or 2, wherein the suspension is formed of sheet metal.

4. A suspension as defined in claim 1 or 2, wherein the suspension is formed of impregnated fabric material.

5. A suspension as defined in any one of claims 1 to 4, wherein the annulus includes at least 24 of said structures.

6. A suspension as defined in any one of claims 1 to 5, wherein said inner and outer fold lines lie in a common plane perpendiculartothe axis.

7. A suspension for supporting an edge of an acoustic diaphragm with respect to a fixed supporting member, substantially as herein described with reference to Figures 1 to 8 or Figure 9 of the accompanying drawings.