GB2169471A - Acoustic diaphragm - Google Patents

Abstract

An acoustic diaphragm comprises a core 11 disposed between a pair of skin members 13. The core is concentrically corrugated to have alternately slanting portions converging to concentric lines 21. Each skin member 13 is bonded to the core at the concentric lines on the respective face of the core. The core is preferably formed from sheet material folded along the concentric lines. Radial reinforcing ridges 17 may also be provided. A method of manufacturing the acoustic diaphragm is also disclosed. <IMAGE>

Description

SPECIFICATION Acoustic diaphragm This invention relatesto an acoustic diaphragm and to a method of producing an acoustic diaphragm.

Planar acoustic diaphragms have several advantages over conventional conical and dome-shaped acoustic diaphragms, including a higher stiffness-to- mass ratio and a linear phase response which eliminates the so-called "cavity effect" of conventional conical and dome-shaped diaphragms.

Known planar acoustic diaphragms are of sandwich construction, having a core disposed between skin members. In one known arrangement, the core is of a conventional honeycomb structure formed of metal foil. In another arrangement, the core is of a hon eycomb structure which is axially symmetrical. In still another arrangement, the core is formed of an elongated web material bent alternatingly and succes sivelytherebyto have a plurality of radial projections.

There are various advantages and disadvantages with acoustic diaphragms which have these known cores. However, these acoustic diaphragms each have the deficiencythatthe diaphragm is unfinished at its perimeter; that is, interstices within the core are exposed atthe perimeter of the diaphragm. As a consequence of this, each skin member is notfully supported at its perimeter.

The present invention seeks to provide an acoustic diaphragm which is of relatively simple construction and which is finished at its perimeter.

In one form the invention resides in an acoustic diaphragm having a sandwich structure comprising a core disposed between a pair of skin members, the core being concentrically corrugated to have alternately slanting portions converging to concentric lines, each skin member being bonded to the core at the concentric lines on the respective face of the core.

With this arrangement, there is line contact between the core and each skin member. The effect ofthis is that the skin members in combination with the corrugated core provide a structure in the form of a truss. This provides the diaphragm with a relatively high degree of radial stiffness.

Preferably, the core is formed from sheet material folded along said concentric lines. The core is preferably folded from a blank which is circular with a sector thereof removed.

The outermost slanting portion provides a perimeterwall for the acoustic diaphragm. This provides the acoustic diaphragm with a finished perimeter. The finished perimeter ofthe acoustic diaphragm provides a reinforced edge f6r attachmentto a suspension system of a speaker.

Atthe outer edge of one or each skin memberthere may be provided a flange which is folded against and bonded to the adjacent slanting portion of the core.

Preferably, at least one skin member is provided with radially extending reinforcing ribs for enhanced lateral rigidity. Preferably both skin members are provided with the ribs.

The slant height of each slanting portion may be varied to accommodate a non-planar skin member, if desired.

In another form the invention resides in a method of manufacturing an acoustic diaphragm having a concentrically corrugated core sandwiched between a pair of skin members, comprising the steps of: forming a blank of sheet material, the blank being circular with a sectorthereof removed thereby to provide the blank with a pair of radial edges, folding the blank about a plurality of concentric fold lines thereby to provide the concentrically corrugated core with the radial edges of the blank in juxtaposition, and bonding the skin memberstothecore.

Preferably, the radial edges are bonded together; whilethisis not essential, itdoes provide improved diaphragm performance at certain frequency ranges.

Preferably, the blank is folded aboutthefold lines in a pluralityoffolding stageswiththe radial edgesofthe blank moving towards each other during each folding stage.

The fold lines may be constituted by lines of weakening formed on the blank.

In still another form the invention resides in a method of making an acoustic diaphragm having a concentrically corrugated core sandwiched between a pair of skin members, comprising the steps of: forming a plurality of blanks of sheet material, each blank being circular with a sectorthereof removed wherebythe blank is provided with a pair of radial edges, folding each blank about a plurality of concentric fold lines therebyto provide a core portion concentrically corrugated, assembling the core portions with each radial edge of each core portion abutting a respective one ofthe radial edges of another core portion thereby to constitute the core, and bonding the skin membersto the core.

Preferably, the abutting radial edges of the core portions are bonded together.

Preferablythere are two core portions each of semi-circular configuration. Preferably each blankis folded aboutthefold lines in a plurality offolding stages.

The invention will be better understood by reference to the following description of several specific embodiments thereof as shown in the accompanying drawings in which: Fig. lisa perspective view of an acoustic diaphragm constructed in accordance with the first embodiment; Fig. 2 is a perspective view ofthe acoustic diaphragm of Fig. 1 with partofthe diaphragm cut-away; Fig. 3 is a sectional view ofaspeakerincorporating the diaphragm of Fig. 1, with the diaphragm shown at an enlarged scale in relation to the remainder to the speakerforthe sake of clarity; Fig. 4 is a sectional perspective view of a core forthe acoustic diaphragam of Fig. 1; Fig. 5 is a perspective view of a blankfrom which the core of Fig. 4 is formed;; Figs. 6,7,8 and 9 are schematic views illustrating various stages in the production ofthe core member of Fig.4; Fig. 10 is a perspective view of one die of a progressive die set and a blank being folding thereon; Fig. 11 is a schematic view of strip stockwith several blanks at various stages during folding thereof; Fig. 12 is a pespective view af a portion of a core of an acoustic diaphragm according to a second embodiment; Fig. 13 is a schematic side view of an acoustic diaphragm according to a third embodiment; Fig. 14 is a schematic side view of an acoustic diaphragm according to a fourth embodiment; and Fig. 15 is a schematic side view of an acoustic diaphragm according to a fifth embodiment.

Referring to the drawings and in particularto Fig. 1 thereof, an acousticdiaphragm 10 according to the first embodiment is of sandwich construction, comprising a core 11 disposed between a pair of skin members 13. The core 11 is folded from a blank 15 of sheet material which may be in theform of metal foil such as aluminium ortitanium foil, ora foil of composite or plastics materials. Likewise, the skin members may beformed of metal foil or a foil of composite or plastics material.

Each skin member 13 is of circular configuration and is formed with radially extending reinforcing ribs 17to provide the skin memberwith lateral rigidity. In the illustrated arrangement, the reinforcing ribs are embossed intheskin members.

The core 11 is concentrically corrugated (as shown in the drawings) to have alternating slanting portions 19 with adjacent slanting portions converging to a respective common line 21. The common lines 21 are concentric, as best seen in Figs. 2 and 4 ofthe drawings. In practice,there would normally be con siderablymorecorrugationsformed in the core than are shown in the drawings.

The skin members 13 are each bonded to the core at the common lines 21 on the respective side ofthe core.

This provides line contact between each skin member and the core.

The blank 15from which the core is folded is shown in Fig. Softhe drawings. The blank is of circular configuration with a sector thereof removed so as to provide the blankwith a pair of radial edges 23. The common lines 21 constitute fold lines about which the blank is progressively folded to assume the configuration shown in Fig. 4 ofthe drawings. The blank may be provided with lines of weakening which constitute the fold lines if so desired. The lines of weakening may be etched, scored orotherwiseformed on the blank.

As the blank is progressivelyfolded, the radial edges 23 progressively move towards each other with each folding stage. In this embodiment, the core is formed from a single blank and the radial edges 23 move into juxtaposed relation, as best seen in Fig. 4.

While it is not essential, the radial edges are preferably bonded togetherwhen in juxtaposed relation. The bonding may be accomplished by means of an adhesive substance.

Figs. 6, 7, Sand 9 iilustrate several of the folding operations which the blank 15 undergoes before it assumes the configuration ofthe core 11 as shown in Fig. 3. The folding operations are performed on dies 25 which have shaped impressions 27 againstwhich the blank is pressed to progressivelyform the core. The blank may be pressed against each die by any appropriate means such as a pressing die of com plementaryconfiguration or by suction orfluid pressure. The impressions in the dies are positioned so thatthe pitch between the fold lines 21 on successive dies progressively reduces and the depth ofthe impressions progressively increases, as shown in Figs. 6,7,8 and 9. This serves to increase the extent offoldingoftheblankwith eachfoldingoperation.

Referring to Fig. 11, a plurality of blanks may be formed on a strip stock 29 which is fed to the progressive die set and progressively advanced therealong.Afolding operation is performed on each blank at each die in the set and after completion of the folding operations each blank (which atthatstage is in theform ofthe core) is severed from the strip.

The outermost slanting portion 19a of the core provides a perimeter wall for the completed acoustic diaphragm. The skin members 13 each terminate adjacent a fold line ofthe outermost slanting portion, as best seen in Fig. 2 ofthe drawings. As a consequence ofthis, each skin member is supported at its periphery. This provides the diaphragm with a degree of circumferential rigidity which can be beneficial when the diaphragm is mounted in a speaker.

In Fig. 3 ofthe drawings, the acoustic diaphragm 10 is shown incorporated into a speaker31. The speaker 31 has a frame 33 on which the acoustic diaphragm is mounted by a suspension means 35 of known kind. A coil bobbin 37 is fixed to the inner side ofthe diaphragm at a location which corresponds to the node of the first resonance, as is conventional practice with planar acoustic diaphragms.

In the illustrated arrangementthe suspension means35isshownattachedtothemarginal portion of the skin member at the outer side of the diaphragm. In an alternative arrangement,the suspension means may be attached to the perimeterwall ofthe diaphragm as constituted by the outermost slanting portion ofthe core.

lnthefirstembodimentthecore isofone-piece construction; that is, itisformedfrom a single blank.

In certain circumstances, it may be more convenientto assemblethecorefrom portions which fittogether. In this connectionthere is shown in Fig. 12 ofthe drawings one oftwo core portions 41 which fit togethertoform a coreforan acoustic diaphragm according to the second embodiment. Each core portion 41 is semi-circular thereby having a diametral edge43.Thetwo core portions are positioned togetherwith theirdiametral edges in juxtaposed relationship thereby to provide the core. Preferably, the core portions are bonded together at their diametral edges, although this is not essential. Each core portion is folded from a blank in a mannersimilar to that described in relation to the first embodiment.

However, fewerfolding stages are required to produce each core portion 41 than are required to produce a one-piece core. The blankfor each core portion is circularwith a sector thereof removed, the size ofthe removed sector varying according to the desired shape ofthe core portion.

Referring nowto Fig. of the drawings, the acoustic diaphragm according to the third embodi ment is similarto that ofthefirst embodiment (like reference numerals thereby being used to identify similar parts), with the exception that a flange 45 is provided atthe periphery of each skin member 13.

Each peripheral flange 45 is folded so asto lay against the outermost slanting portion 1 9a ofthe core 11 and is adhesively bonded thereto. This provides the diaphragm with added circumferential rigidity and strength.

Refe rring nowto Fig. i4ofthe drawings, the acoustic diaphragm according to the fourth embodi mentisagainsomewhatsimilartothatofthefirst embodiment, with the exception that the slanting portions 19 are of various slant heights to accommo datethe skin member 13a which is of non-planarform.

Both skin members may be non-planar if so desired.

In circumstances where a diaphragm of relatively largethickness is required, several core members may be stacked one upon another and adhesively bonded together. In this connection, there is illustrated in Fig.

15 ofthe drawings an acoustic diaphragm having two core members 11 a and 11 b stacked one upon the other between the skin members 13.

From the foregoing it is evident that the present invention provides an acoustic diaphragm which is of comparatively simple construction and relatively high stiffness in both the circumferential and radial directions.

Although the invention has been described with reference to several specific embodiments it is not limited thereto and various alterations and modifications may be made without departing from the scope of the invention.

Claims (17)

CLAIMS:

1. An acoustic diaphragm having a sandwich structure comprising a core disposed between a pair of skin members, the core being concentrically corrugated to have alternately slanting portions converging to concentric lines, each skin member being bonded to the core atthe concentric lines on the respective face of the core.

2. An acoustic diaphragm according to Claim 1 wherein the core is formed from sheet material folded along said concentric lines.

3. An acoustic diaphragm according to Claim 1 or 2 wherein at least one skin member is provided with a flange at its outer edge, the flange being folded against and bonded to the adjacent slanting portion of the core.

4. An acoustic diaphragm according to any one of the preceding claimswherein each skin member is planar.

5. An acoustic diaphragm according to any one of claims 1 to 3 wherein at least one skin member is non-planar, the slant height ofthe slanting portions being varied to accommodate the non-planar skin member.

6. An acoustic diaphragm according to any one of the preceding claims wherein at least one skin member is provided with radially extending reinforcing ribs.

7. An acoustic diaphragm substantially as herein described with reference to the accompanying draw ings.

8. A method of manufacturing an acoustic diaphragm having a concentrically corrugated core sandwiched between a pair of skin members, comprising the steps of: forming a blank of sheet material, the blank being circularwith a sector thereof removed thereby to provide the blank with a pair of radial edges, folding the blank about a plurality of concentric fold lines thereby to provide the concentrically corrugated core with the radial edges ofthe blank in juxtaposition, and bonding the skin members to the core.

9. A method according to Claim 8 further compris ingthestepofbondingsaid radial edgestogether when in juxtaposition.

10. A method according to Claim 8 or 9 wherein the blank is folded aboutthefold lines in a plurality of folding stages with the radial edges of the blank moving towards each other during each folding stage.

11. A method according to Claim 8,9 or 10 wherein the fold lines are constituted by lines of weakening formed on the blank.

12. A method of making an acoustic diaphragm having a concentrically corrugated core sandwiched between a pair of skin members, comprising the steps of: forming a plurality of blanks of sheet material, each blank being circu larwith a sectorthereof removed whereby the blank is provided with a pair of radial edges, folding each blank about a plurality of concentricfold line thereby to provide a core portion concentrically corrugated, assembling the core portions with each radial edge of each core portion abutting a respective one of the radial edges of another core portion thereby to constitute the core, and bonding the skin members to the core.

13. A method according to Claim 12further comprising the step of bonding said abutting radial edges ofthe core portions together.

14. A method according to Claim 12 or 13wherein each blank is folded about the fold lines in a plurality of folding stages.

15. A method according to Claim 12, or 14 wherein the fold lines are constituted by lines of weakening formed on the blank.

16. A method according to anyone of Claims 12to 15 wherein there are two core portions each of semi-circular configuration.

17. A method of making an acoustic diaphragm substantially as herein described with reference to the accompanying drawings.