GB2358545A - Partially hollow loudspeaker components - Google Patents

Abstract

A loudspeaker component such as a diaphragm, surround, suspension or chassis, formed as a one piece moulding in a single material. At least one portion of the component is of a hollow material and at least one other portion is of a solid material (a hollow material includes one with an internal void as well as a material with an internal cellular structure e.g. a foam). The hollow portions are positioned in an acoustically active component to control the acoustic performance of the component e.g. to suppress bell-mode resonance. In the case of a speaker diaphragm, the hollow portions can take the form of annular or radially extending ribs, or can be positioned around the periphery of the diaphragm.

Description

2358545 LOUDSPEAKER This invention relates to loudspeakers, to their

component parts and to the manufacture of such components.

The design of loudspeakers, especially for high-volume applications such as motor vehicle audio systems, is a compromise between acoustic performance and cost. Both are a function of the physical characteristics (stiffness, damping and weight) of the loudspeaker diaphragm. Conventionally loudspeaker diaphragms are made of specialist paper or fibre-based materials in order to achieve acceptable stiffness and damping without an excessive weight penalty. Excessive weight in the diaphragm is particularly undesirable because the speaker then requires more electrical power to produce a given acoustic output, necessitating a more powerful magnet and a more powerful amplifier, both of which increase the cost. Attempts to use plastics materials instead of paper have encountered difficulties that, if the plastics material is made thin enough to avoid excessive weight, the acoustic performance is unacceptable.

one preferred embodiment of the present invention addresses 20 this problem, although the invention can be applied to other loudspeaker parts as well.

The invention provides in one aspect a loudspeaker component formed as a one-piece moulding in a single material, in which at least one portion of the component is of hollow material (as herein defined) and at least one other portion is of solid material.

By "hollow" we mean either hollow in the usual sense, i.e.

2 having an internal void, or having an internal cell' i structure formed e.g. by foaming. The cellular struc i can itself contain voids. As stated, the component ma a loudspeaker diaphragm, and the hollow portion may be p' tioned to modify the acoustic performance of the diaphr The hollow portion, especially if of internally foameo cellular construction can be significantly stiffer thir solid portion of the same weight, depending on the choicia material. Alternatively, if of flexible material it provide high damping.

The hollow portion may be positioned to suppress bell-im resonances of the diaphragm. Thus the hollow portion May annular, and may be radially inward of the edge of i I diaphragm and centred on the axis of the diaphragm.

configuration may be particularly suitable for ellipti, diaphragms. Whilst usually the diaphragm will be generla.. I conical in form, and cirular or elliptical in plan, it 4 also possible that the diaphragm may be made generally and/or have a perimeter of a shape other than circul# 20 elliptical.

The hollow portion may be disposed around the periphez,( the diaphragm, and may constitute a surround integra formed with the diaphragm, and provided with a periphe flange for mounting the diaphragm to a chassis of 25 loudspeaker.

Alternatively or in addition, the hollow portion may b radially-extending hollow rib. Such ribs normally would angularly spaced around the diaphragm. The diaphra i surround with its solid flange may be formed on its owi 1 3 separate component. The diaphragm-surround may comprise circumferentially-extending hollow portion which is substantially arcuate in radial cross-section.

The loudspeaker component according to the invention may be 5 a diaphragmsurround or a voice-coil suspension.

The suspension may be apertured to permit the passage of air though it.

The suspension may have a radial cross-section which at least in part is serpentine in form, at least a portion of which is of said hollow material.

Whilst the invention is seen as of particular value for dynamic speaker components, it can be applied also to structural parts of the speaker. Thus the invention may also be applied to a loudspeaker chassis. The resulting component can be notably lighter than a comparable metal chassis or indeed a solid plastics chassis of comparable stiffness.

The said portion of hollow material may have a foamed interior and an unfoamed skin.

The component may be formed of a material exhibiting significantly less damping than polypropylene, such as ABS or polycarbonate.

The invention also provides a method of manufacturing a component as set forth above, which includes injecting said material into a mould tool having parts defining a first gap corresponding to the solid portion of the component, and 4 parts at least one of which is moveable defining a se nd gap corresponding to the hollow portion of the compong t, subsequently withdrawing the moveable part of the mould ol to increase the second gap, and expanding the material the increased gap by foaming or blowing to form the hc,'..ov portion of the component.

The method may also comprise reducing a gap defined in. hE mould tool after the gap has received said material.

The invention will now be described merely be way of exa4)le 10 with reference to the accompanying drawings, wherein:

Figure 1 shows the component parts of a loudspeaker, iy,i ar exploded view; Figures 2A and 2B respectively show part of a conventi,Pial loudspeaker diaphragm- surround and part of a diaphrmsurround according to the invention, both in radial ci:) s section; Figures 3A and 3B respectively show part of a convent al loudspeaker suspension and part of a loudspeaker suspenl3.,pr according to the invention, both in radial cross-sectiop; Figures 4A and 4B respectively show plan and perspec VE views of a loudspeaker diaphragm according to the invent. n; Figure 5 shows another diaphragm according to the invent. ' n; Figure 6 shows bell-mode resonance in a speaker diaphr9; Figure 7 is a section through a speaker component accord ncf to the invention; and, Figure 8 is a section through a loudspeaker having a flat diaphragm according to the invention.

Referring to Figure 1, a loudspeaker consists principally of a frusto-conical diaphragm 10 having a surround 12 by which it is affixed to an outer ring 13 of a chassis 14 by adhesive together with a front gasket 18, card ring 20 and rear gasket 22. Registering holes 16 permit the speaker to be screwed to a vehicle door or loudspeaker cabinet.

The outer ring of the chassis is joined by webs 24 to an inner ring 26. An inner margin of the diaphragm 10 is connected to a bellows-like voicecoil suspension 28. In this embodiment the voice-coil suspension 28 also is attached to the inner ring 26 of the chassis. A small is secondary diaphragm 29 with an internal dome can be fitted at the inner margin of the diaphragm 10 to augment its high frequency performance.

A voice coil former 30 carrying a voice coil is attached to the inner margin of the diaphragm 10 and extends rearwardly into a magnetic gap formed in a magnetic circuit consisting of a top plate 32, magnet 34 and pole plate 36. The ends of the voice coil are taken to a connector 38, to which an audio signal is supplied for operation of the speaker.

All parts except the connector 38 are of course arranged coaxially on the axis of the diaphragm 10. The voice-coil suspension centres the voicecoil 30 in the magnetic gap.

Referring to Figure 2A, in a conventional loudspeaker the 6 diaphragm-surround 12 can be of elastomeric material.,I surrounds are waterproof (important in loudspeakers j installation in a vehicle door), of consistent perf orma( and reliable. They also can be moulded directly onto diaphragm 10, thus eliminating the need for adhesive. ever, they are too heavy, and provide poor damping.

In Figure 2B the diaphragm-surround 12 comprises ec flanges 40, 42, the former being moulded to the diaphrac the latter being for attachment to the outer ring of!t chassis 14 as already described. The flanges 40 ar solid plastics elastomeric or resilient polymeric mater Between them, and moulded in the same material at the O i time, is an arcuate section 44 of foamed construction. T1 foamed section provides greater damping than the con.r( is tional surround, and is also lighter in weight. If desirt different regions of the arcuate portion 44 may be prov.,L( with different degrees of foamed construction, or 1 arcuate portion may be foamed in discrete spaced-ap regions with solid regions in between.

Referring to Figure 3A, the suspension or spider 2 Figure 1 is shown in radial halfsection. It convention. is of resin- impregnated cloth material, and is of belli like configuration so as to be of serpentine cross-sect!.( Resin-impregnated spiders deteriorate over time due toy hardening and fatigue cracking of the resin as the diaph-- vibrates. Elastomeric spiders can be moulded to the cox,,( shape but are not sufficiently dimensionally stable iY time which is a serious disadvantage in that the voice p is a close fit in the magnetic gap, and must be accurati located radially and axially if contact with the magnet,, 7 top plate or the pole plate is to be avoided. A peripheral flange 46 is provided for attachment to the chassis inner ring 26, and the inner margin 48 is moulded or fixed with adhesive to the inner rim of the diaphragm 10 or voice coil former 30.

In Figure 3B, in a suspension or spider according to the invention, the peripheral flange 46 is of solid material, but the corrugated portion 50 is of foamed construction. The spider is formed as a single-piece moulding as described later. A suitable material is polyester.

The foamed portion may be continuous around the spider, or may be intermittent and interspersed with unfoamed (solid) sections. Suitable configurations of foamed and solid parts can be determined by known vibration simulation and finite is element analysis techniques, to result in a light, welldamped component with excellent "run-in,, characteristics ie. it does not change in stiffness during the life of the speaker. Holes 52 are provided at intervals through the spider so that air can pass through it, thereby reducing acoustic distortion which may occur if the spider is airtight. Although shown as lying in the same sectional place in Figure 3B, it may be found advantageous to the acoustic performance of the suspension if the holes 52 are angularly staggered.

It is important that in operation the diaphragm responds to the input acoustic signals by vibrating coherently and not "breaking-up", which would introduce distortion. Thus the diaphragm 10 may also be formed as a single-piece moulding with solid and hollow portions to modify its acoustic per- formance. For example, as shown diagrammatically in Figure 8 4, radially extending ribs 54 of foamed and/or interii' 1v voided material are equiangularly spaced around a i,,, n diaphragm. The intervening portions of the diaphragm arVe o. solid material. This configuration enables undesired 2' 0., nances to be suppressed, especially with shallow diaplj 4gm shapes. The diaphragm- surround 12 can convenientl, be moulded onto the diaphragm or possibly could be moi-il, e integrally with it at the same time in the same mould,'!, ud using different materials. This technique is known pe i r:SE! in other fields such as computer key pads.

In Figure 5 is shown diagrammatically an elliptical fru 0conical diaphragm provided with a foamed or otherwise hoL portion 56 in the form of a ring intermediate its inner outer mar-gins 58, 60. The ring S6 can be dimensioneo ac positioned to suppress bell-mode resonance, in which,'I a illustrated diagrammatically in Figure 6, an acous icaround the periphery of bE frequency wave 62 travels diaphragm. An intermediate ring may be employed also v a round diaphragm, and radial ribs may be employed i;ar elliptical one. Both may be employed together in ei-bez shape of diaphragm.

A suitable material for a diaphragm according to hE invention is ABS or polycarbonate, which has lower mate,:d'a2 damping than the polypropylene used hitherto. It alsol, kar be adhered better to other parts, and has better resista: CE to high temperatures, to which it may be exposedPier, attaching the surround, suspension or voice coil fox-Air.

Another possible material is polyester.

The hollow regions moulded into the diaphragm enableli h,E 30 necessary damping and stiffness to be provided wh rE 9 required with less reliance on the physical properties of the diaphragm material per se. Careful positioning of the hollow regions permits the production of diaphragms in plastics material which are lighter and shallower than hitherto, without the disadvantages of poor acoustic performance.

The speaker chassis may also be moulded to have hollow and solid parts according to the invention. Thus, for example, the web 24 of the chassis may have a cross-section as shown in Figure 7. The web has an outer unf oamed skin 64, an inner region 66 of foamed material and a central void 68. A light but rigid structure results.

Loudspeaker components according to the invention may be manufactured in accordance with one or more of the methods is described in United Kingdom specifications 2308090 and

2321872, or International specifications W098/16364 and W098/17456. The disclosures of these specifications are incorporated herein by reference. Basically these methods include the steps of injecting moulding material into a die having a first gap or cavity defining what will be the solid part of the component, and a second gap corresponding to the hollow part. The second gap is bounded by a moveable part of the die which is withdrawn a predetermined distance after the material is injected. The material is expanded into the enlarged die cavity, either by foaming if a foaming agent is included in the material, or by blowing with an externallysupplied gas. In the latter case the resulting component does not have a foamed or cellular structure, but has an internal void. When a large degree of expansion is required, an internal void may form even when foaming rather than blowing is employed, resulting in the structure shown in Figure 7. Blowing or foaming may be employed for any of' hE components described, as appropriate to their dimensions LC 1 properties required, and thus they may have either foamed 61 voided hollow portions, or both.

The hollow portion of the components will generally hav ar external skin as at 64, Figure 7. The thickness of i skin can be adjusted by controlling the temperature of11 hE mould, and the time delay between injecting the mate:

into the mould and withdrawing the moveable die part.

Figure 8 illustrates in section a loudspeaker 100 havi)lsr:l, a flat diaphragm (or piston) 102 formed according to the,..,vention so as to have foamed and unfoamed portions!:-,6x example as described for a conical diaphragm with referexce to Figures 5 and 7. Figure 8 is a section through the t diaphragm in a plane where it has radial ly- extending fo,iied ribs 154 on a relatively thin solid membrane 156. A surr:() 104 connects the periphery of diaphragm 102 to the edg6 of chassis (or frame) 106. Central of the chassis 106 pole plate 108, and a magnet 110 is held between pole pI'Liite 108 and top plate 112. A voice coil 114 is surrounded or one side by pole plate 108 and on the other side by magmet and top plate 112. The voice coil 114 is wound on() E end of a former that connects to diaphragm 102. A susl?(- sion (spider) 116 extends between the magnet 110 iLid diaphragm 102. This suspension may be as discussed tt reference to Figure 3b.

In order to achieve a thin section in material containi a significant proportion of a filler such as talc, a techp,(IUE 1 may be adapted wherein the material is injected with] 1, 1 hE i mould slightly open, or with a moveable part defining,! hE thin section slightly withdrawn so as to define a larger gap. This enables the gap to be properly filled with material. Then the die is closed or the moveable part is advanced to define the thin section, excess material being 5 squeezed out to other parts of the mould. Then the previously-described moveable part defining the hollow portion of the component is withdrawn to permit foaming or blowing of the material.

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.

Statements in this specification of the "objects of the invention" relate to preferred embodiments of the invention, but not necessarily to all embodiments of the invention falling within the claims.

The text of the abstract filed herewith is repeated here as part of the specification. A loudspeaker component formed as a one-piece moulding in a single material, in which at least one portion of the component is of hollow material (as herein described) and at least one other portion is of solid material. The hollow portions may be positioned in an acoustically active component to control the acoustic performance of the component.

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Claims (23)

CIAIMS:

1. A loudspeaker component formed as a one-piece moulding in a single material, in which at least one portion ofil the component is of hollow material (as herein defined) and at least one other portion is of solid material.

2. A component as claimed in claim 1, being a loudspqaef diaphragm.

3. A component as claimed in claim 2, wherein the at one hollow portion is positioned to modify the acoustic orl p, formance of the diaphragm.

4. A component as claimed in claim 3, wherein the at 4st one hollow portion is positioned to suppress bell-ade resonance of the diaphragm.

5. A component as claimed in claim 2, comprisino, radially-extending hollow rib as said at least one portn.

6. A component as claimed in claim 2, wherein the at leNst one hollow portion is annular.

7. A component as claimed in claim 6, wherein the at 1 'st one hollow portion is disposed at the periphery of hE diaphragm.

8. A component as claimed in claim 6, wherein the at 1,p' st one hollow portion is disposed radially inwardly of hE periphery of the diaphragm.

9. A component as claimed in claim 2, wherein the Ia- 13 phragm is generally circular or elliptical in plan.

10. A component as claimed in claim 2, wherein the diaphragm is generally flat.

11. A component as claimed in claim 1, being a loudspeaker diaphragmsurround.

12. A component as claimed in claim 11, wherein the surround comprises a circumferentially extending hollow portion which is substantially arcuate in radial cross-section.

13. A component as claimed in claim 1, being a loudspeaker voice coil suspension.

14. A component as claimed in claim 13, wherein the suspension is apertured to permit the passage of air though it.

15. A component as claimed in claim 13, wherein the suspension has a radial cross-section which at least in part is serpentine in form, at least a portion of which is of said hollow material.

16. A component as claimed in claim 1, being a loudspeaker chassis.

17. A component as claimed in claim 1, wherein said portion of hollow material has a foamed interior and an unfoamed skin.

18. A component as claimed in claim 1, being made of a material exhibiting significantly less damping than polypropylene.

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19. A component as claimed in claim 18, wherein he material is ABS or polycarbonate.

20. A method of manufacturing a component as claimeo ill claim 1, including injecting said material into a mould tpol having parts defining a first gap corresponding to the portion of the component, and parts at least one of which moveable defining a second gap corresponding to the hc)l0%7 portion of the component, subsequently withdrawing -ihe moveable part of the mould tool to increase the second and expanding the material into the increased gap by foan 1 ng or blowing to form the hollow portion of the component.

21. A method as claimed in claim 20, also comprisingi he step of reducing a gap defined in the mould tool after -:hE! gap has received said material.

22. A loudspeaker comprising a component as claime(j ir claim 1. 1

23. A loudspeaker, a loudspeaker component or a methoo rof manufacturing a loudspeaker component, substantially';a,.z herein described.