NZ330777A

NZ330777A - Loudspeaker with a planar diaphragm having a bending strength along one axis which is greater that along a second axis perpendicular to the first axis

Info

Publication number: NZ330777A
Application number: NZ330777A
Authority: NZ
Inventors: Christopher Colin Lock; John Frederick Corey; Graeme Oliver Jones; Kelly Charles Waterman
Original assignee: Slab Technology Ltd; Christopher Colin Lock; John Frederick Corey; Graeme Oliver Jones; Kelly Charles Waterman
Priority date: 1998-06-22
Filing date: 1998-06-22
Publication date: 1999-08-30
Also published as: KR100492945B1; KR20010071586A

Description

<div class="application article clearfix" id="description"> Patents Form # J NEW ZEALAND Patents Act 1953 COMPLETE SPECIFICATION AFTER PROVISIONAL # 330777/332328/333833 DATED 22 Junel 998/13 October 1998/21 January 1999 TITLE Loudspeakers We Slab Technology Limited Address 454 Albany Highway Albany. Auckland, New Zealand Nationality A New Zealand company do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following SU,tCmCnt i / OF N°/EW0FFicTj I • *JUN 1999 I iM'^ iwi* 111 ioni inso | _ I i h r> r~.. I -2- 330 / »•* r 5 10 ABSTRACT OF THE DISCLOSURE LOUDSPEAKERS A flat panel rectangular or elliptical loudspeaker has one or more diaphragms 14,15, 15 made of double skinned fluted polypropylene copolymer (core flute) or corrugated cardboard, having a longitudinal bending strength greater than the transverse bending strength The diaphragm is vibrated by a driver unit 16 which comprises a magnet 17 and voice coil 18 In this version the magnet 17 is mounted on the rear diaphragm 2q 15 and the voice coil 18 is mounted on the front diaphragm 14. The two diaphragms 14,15 are mounted at their edges to a frame 11 with the driver unit 16 mounted in the space enclosed by the frame and the diaphragms 25 30 35 T421XCS1 799/JM/iv - ws inilllluual fhuferty office OF NZ 2 1 JUL 1999 -JI?C_EIVED -3- ^ FIELD OF THE INVENTION This invention relates to loudspeakers, and is applicable particularly, but not exclusively to loudspeakers intended to be hung adjacent a wall, in the manner ot a picture 10 BACKGROUND Flat loudspeakers have been known tor many years, for example Iree-standing 15 electrostatic loudspeakers However, such loudspeakers have had to be large and therefore obtrusive in order to produce a satisfactory sound level They have been expensive and have had a less than desirable sound frequency response and sound distribution pattern 20 Various other types o' flat, wall-mountable loudspeakers have been devised, but again they have suliered variously from inferior frequency response or stereophonic performance 25 STATEMENT OF THE INVENTION According to one aspect of the present invention there is provided a loudspeaker including a substantially planar first diaphragm which can be vibrated so as to radiate 30 sound trom at least the front face thereof, and a driver unit operable by a varying electric current in order to generate a varying force on the first diaphragm, the force varying in a manner related to the varying electric current, characterised by the driver unit being connected to the first diaphragm at one or more selected positions or 35 mounted to structure which is in turn connected to the diaphragm at one or more selected positions T4 J I 1\W 3 699/wP 10 15 Preferably the material of the diaphragm has a bending strength in a single plane along a tirst axis which is greater than along a second axis which is perpendicular to the first axis Preferably the material of the diaphragm has a bending strength in one direction of the plane of the material which is significantly greater than the bending strength along a line in the plane of the material at right angles to the first direction In its most preferred form it has a longitudinal bending strength which is about twice its transverse bending strength, which is particularly suitable to panels which are rectangular or elliptical Preferably the loudspeaker includes a substantially rigid peripheral frame having a front face and a rear face, said first diaphragm extending right across the front face and a rear diaphragm extending right across the rear face whereby the interior space of the 2Q loudspeaker is substantially enclosed. Conveniently the driver unit is located within said space remote from the frame Advantageously the driver unit is located outside said space remote from the frame 25 Preferably the driver unit is connected to both of said diaphragms whereby the driver unit will apply varying force, corresponding to the varying electric current, to said diaphragms and cause at least one of said diaphragms to flex and emit an acoustic 30 signal from the face of the diaphragm exterior of the loudspeaker Conveniently both said diaphragms are flexible and the driver operates the diaphragms in bi-polar mode, that is they move outwards together or inwards together. 35 Preferably one of said diaphragms is flexible and the other is n t421ics1 799/jm/lv - « INTELLECTUAL PROPERTY OFFIGl W OF NZ 2 1 JUL 1999 RFCEIVED - 5 - Conveniently the driver unit is mounted to the diaphragm at said one or more selected positions, said positions being remote trom the peripheral edge ol the diaphragm 5 Advantageously the driver unit is mounted on a body which is mounted on pillars to the diaphragm at said positions Prelcrably said positions arc selected so that flexure of the diaphragm in one or more oi ^ its natural modes of vibuition is not impeded. Said lirst diaphragm and/or said rear diaphragm may be of double skinned polypropylene copolymer, and may be approximately 3mm thick 15 Conveniently the or each diaphragm is approximately 500 grams or less per square metre, and may have a tensile strength of around 28 MPa or more and may have a Shore hardness ol 67 or more 20 Prelcrably the surlace ol the or each diaphragm is treated with a corona discharge to assist adhesion ol paint or paper thereto, or of the diaphragm to the frame Conveniently the or each diaphragm has longitudinal ribs forming part of its structure 25 perhaps on one lace although in its most preferred form they are internal (le covered by smooth lront ant rear faces) Preferably these ribs are provided by a core of corrugated material or the like and may be square or rectangular and each edge is around 400mm long 30 Advantageously the driver unit includes two co-axial voice coils, each fastened to a different one of said diaphragms, the voice coils co-acting with a magnet suspended centrally between said voice coils Conveniently the or each diaphragm is slightly fluted or corrugated or slightly curved. -6- so as to provide a modihed acoustic performance of the loudspeaker The interior ol the loudspeaker may constitutes a sealed box Alternatively one or more ports or vents may be provided through the frame or through one or both or said diaphragms Preferably the first diaphragm is made of a sheet of extruded plastics material having ^ integral front and skins joined by closely spaced parallel walls normal to said skins In another aspect the invention provides a loudspeaker including a substantially planar diaphragm which can be vibrated so as to radiate sound from at least the front face 15 thereof, and a drivfcr unit operable by a varying electric current in order to generate a varying lorce on the diaphragm, the force varying in a manner related to the varying electric current, in which the diaphragm is made of front and rear parallel sheets of material, said sheets being spaced apart by a plurality of walls extending between said sheets and said walls being parallel to each other and extending substantially normal to said sheets, or being of generally rhomboidal or sinusoidal corrugated form Prelcrably the diaphragm is ol double skinned polypropylene co-polymer and the walls are substantially normal to said parallel sheets 25 Alternatively, the diaphragm is ot paper or cardboard, said walls being of substantially corrugated lorm and being fastened by adhesive to the inner opposing laces of the parallel sheets 30 Conveniently the driver unit includes a magnet, one pole of which is in magnetic continuity with a yoke and the other pole of which is positioned from the yoke by an air gap through which gap a voice coil is operable, the voice coil being attached to drive 35 the diaphragm 4M'I j U ) a Jp -7- Prelerable the magnet is a cylindrical permanent magnet and the yoke is co-axial therewith, said air gap being annular More preferably the magnet is a high strength permanent magnet such as a neodymium magnet Advantageously, the yoke is made from low oxygen pure iron annealed very slowly in hydrogen ^ Conveniently the voice coil has more windings per unit length thereof away from that axial part ol the voice coil which is in said air gap when no electric current is passed through the windings 15 For this purpose, the voice coil winding is a single layer, with the windings spaced apart in the region of said axial part Preferably the voice coil is made of pure copper (although aluminium wire could also be used) Alternatively or in addition, more than said single layer is wound at regions of the voice coil lurther Irom said axial part According to another aspect of the present invention there is provided a loudspeaker including a diaphragm which can be vibrated so as to radiate sound from at least the 25 Iront lace thereol, and a driver unit operable by a varying electric current in order to generate a varying force on the diaphragm, the force varying in a manner related to the varying electric current, in which a voice coil of the driver unit is connected to said diaphragm, by means of a panel of material, said panel being of a material and having 30 dimensions such that at a low range of audio frequencies, the voice coil and at least that part ol the diaphragm adjacent the panel move substantially at the same amplitude and phase, while at a higher range of audio frequencies at least said part of the diaphragm and a part of the panel adjacent thereto move at a lower amplitude and /or at 35 a different phase from the voice coil, whereby at said higher range a substantial part of the sound emitted by the loudspeaker is radiated from a face of the panel adjacent the r J/1 ' /i n'» >/ ji voice coil Prelcrably the diaphragm is a planar diaphragm Conveniently a sheet of damping material is connected from a stationary part of the loudspeaker to said part ol the diaphragm adjacent the panel or to the panel The damping material may be cloth or cloth based Prelcrably the damping material is porous or perforated so as to allow the passage of air therethrough BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of the invention is described, by way of example only, with reference to the accompanying drawings in which Figure 1 is a front view of a loudspeaker, according to the invention, and Figure 2 is a cross-section in a vertical plane along the line II-II in Figure 1, and Figure 3 shows a rear and side views of an alternative embodiment, Figure 4 is a partial perspective view of a component of the loudspeaker, Figure 5 is a cross-section of a further embodiment, Figure 6 is a first rear view of the embodiment shown in Figure 5, and Figure 7 is a second modified rear view of the component shown in Figure 4 T421JN2J (5^9 Jp -9- Figure 8 is a transverse section through another embodiment Figure 9 is a side view ol a voice coil shown in section in Figure 8 DESCRIPTION 10 EXAMPLE 1 In the drawings, a Hat loudspeaker 10 includes a square peripheral frame 11 conveniently made ol medium density libreboard Each external edge of the frame 11 is conveniently 400mm long The frame is suspended by wires or cords 12 attached to 15 loops or other fasteners 13 at the top of the frame 11 As seen, particularly in Figure 2, the Iront of the loudspeaker 10 is covered by a lront diaphragm 14 which is attached and sealed around the edges thereof by a suitable -,0 adhesive to the lront lace of the frame 11 Similarly the rear of the loudspeaker 10 is covered by a rear diaphragm 15 attached and sealed to the rear face of the frame 11 by an adhesive Thus, the interior of the loudspeaker 10 constitutes a sealed box Typically, the thickness between the tront and the rear faces of the diaphragm 14 are 30 millimetres tor a 400 millimetres square loudspeaker 25 It has been found that a suitable material for the front and rear diaphragms 14, 15 is a double skinned sheet made from a polypropylene copolymer approximately 3 millimetres thick and approximately 500 grams per square metre or less Preferably the 30 sheet is fluted, has a tensile strength ol around 28 MPa or more and shore hardness of 67 or more The material preferably has a corona discharge treated surface to assist adhesion of paint, or wallpaper to the exterior surfaces of the diaphragms 14, 15 and to assist adhesion of the interior surfaces of the diaphragms 14, 15 to the frame 11 The 35 sheet is preferably a laminate having a core formed from ribs, tubes or corrugations, or the like One such a material is known as "core flute" material from the shape ol the - 10- internal longitudinal "nutes" or corrugations - see Figure 4 (discussed below) Another practical material is lightweight corrugated card 5 A driver unit 16 is positioned adjacent the centre ot the diaphragms 14, 15 The driver unit is similar to those used in conventional cone-type loudspeakers and includes a magnet 17, whu h can be a permanent magnet or an electromagnet, and a coacling voice coil IS The voice coil IS carries the usual winding connectcd by leads 19 to terminals 20 on the icar oi the loudspeaker 10 The magnet 17 is Listened, lor example, by an adhesive to the interior surlace ot the rear diaphragm 15 and the voice coil IS is Listened to the interio" surlace ot the lront diaphragm 14 The dimensions ol the drivei unit 16 and the spacing ol the lront and rear diaphragms 15, are arranged so that the 75 voice coil IS is in the correct operative position relative to the magnet 17, and properly centered therein Depending on the acoustic properties required trom the loudspeaker 10, the interior -)q thereol may be at least partly tilled with tibrous or other sound absorbent material or may be lett empty Similarly, one or more ports or vents may be provided through the frame 11 or the diaphragms 14, 15 Although the loudspeaker 10 has been shown as being square, it could be circular, 25 elliptical, rectangular, polygonal or and other suitable shape It required more than one driver unit 16 may be provided as suitable locations inside the loudspeaker 10 In another embodiment, the front diaphragm 14 or the rear diaphragm 15 may be of 30 substantially rigid material Furthermore, the magnet 17 may be fitted to the tront diaphragm 14 and the voice coil IS to the rear diaphragm 15 For some purposes it may be preferable to provide two coaxial voice coils 18 each 35 fastened to a ditlerent one of the diaphragms 14, 15 and coacting with a centrally suspended magnet 17 Conversely, two magnets 17 can be provided on the diaphragms N i n • » rt -11 - 14, 15 coacting with a centrally suspended voice coil IS Either surlacc ol each diaphragm 14, 15 may be slightly I luted and instead ol either diaphragm being llat, it could be corrugated or otherwise curved so as to provide a modilied acoustic perlormance ot the loudspeaker 10 10 EXAMPLE 2 In figure 3 the frame 11 and rear diaphragm 15 are omitted The magnet 17 is mounted on a plate 21 which is mounted on the diaphragm 14 on pillars 22 The pillars 22 are at carefully selected positions on the diaphragm 14, so that they do not impede flexure of 15 the diaphiagm in one of its natural modes, for example as shown by the line 23 The magnet 17 may be mounted between the plate 21 and diaphragm 14, or on the rear ol the plate 21, as shown The loudspeaker shown in Figure 3 may be suspended from the top edge of the diaphragm 14 or Irom the plate 21 or pillars 22 Figure 4 shows a preferred construction for the front diaphragm 14 It comprises an integral extrusion ol polyethylene around 3-5mm thick and having front and rear skins 25 25,26 joined by continuous iongitudmal walls 27 with air spaces therebetween By this construction, the material ot the diaphragm 14 is anisotropic and has a longitudinal bending strength which may typically be around twice the transverse bending strength Thus, this material is particularly useful m the construction of rectangular loudspeakers, 30 lor example those having sides of 200mm x 100mm long Larger or smaller panels c.in be made using this type of material 35 EXAMPLE 3 Figure 5 shows a loudspeaker having a rigid rear panel 2S of custom wood around "•S7 1JNZJ 69J/JP - 12- 12mm thick, with the magnet 17 fastened in the centre thereof The Irame 11 holds the lront diaphragm 14 at a distance ot around 3-5mm from the front face of the panel 28 The voice coil 18 is held in the gap in the magnet 17 by being fastened in a central hole in the diaphragm 14 The hole is closed by a concave part-spherical cap 29, fastened in the voice coil IS % 10 25 In order to allow desired motion ot the diaphragm 14, the panel 28 (shown in ligure 6) has an array ol holes or ports 30 therethrough The sizes and locations ot the ports 30 are carefully chosen to achieve a smooth frequency response from the loudspeaker 10 Alternative, or additional modification of the frequency response curve is achieved by 15 adhesion ot mass adding material 31, as shown in Figure 7 Suitable material is bituminous sheet loaded with metallic or mineral particles Further adjustment of frequency performance can be obtained by attaching areas of -,0 sound absorbent material 32 to the diaphragm 14 or to the front face of the panel 28, as shown in Figure 7 Supply of electrical signal to the voice coil 18 is conveniently through copper foil strips stuck to one face of the diaphragm 14 EXAMPLE 4 In Figures 8 and 9, a loudspeaker 110 includes a diaphragm 111, to be described later The outer edge ol the diaphragm 111 is gripped by the outer edge of a substantially rigid metal or plastics dish 112 For this purpose, the dish is provided with a flat 113 on which the diaphragm 111 rests, the diaphragm 111 being located by a substantially 3° upright wall 114 and being gripped by an edge portion 115 of the dish 112, which is lolded or rolled over the outer edge of the diaphragm 111 The centre portion ot the dish 112 is formed as a cup 116 in which a cylindrical yoke 117 is located Thus, the dish 112 serves to centre the yoke 117 relative to the diaphragm 111, where it is jj retained by a screw 119 -13- Since the yoke 117 forms part of a magnetic circuit, it is preferably made of low oxygen pure iron which has been annealed slowly in hydrogen A permanent magnet 118 is held coaxial with the voke 117 by adhesive One pole of the magnet 118 is in magnetic contact with the upper interior surface of the yoke 117 and the other pole is adjacent a disc 135, ot the same material and thickness as a flange 120 of the yoke 117 Thus, an annular magnetic gap 121 is formed between the flange 120 and the upper part ol the magnet 118 A cylindrical voice coil 122 extends through the gap 121 The yoke ^ material serves to keep the lines of magnetic flux within the yoke 117, which minimises undesirable external magnetic fields and also concentrates the flux across the gap 121 In an aperture 123 through the diaphragm 111, there is positioned and fastened a panel 15 124 of thin material, such as aluminium typically 0 25mm thick The panel 124 has an out- turned flange 125 iastened to the diaphragm 111 The voice coil 122 is fastened by adhesive into a groove 126 formed in the panel 124, so that the voice coil 122 is held concentrically within the gap 121 Movement of the central area of the diaphragm 111 20 is damped by a damping ring 127 which may be of cloth or cloth-like material, is preferably corrugated and is fastened by adhesive to the upper surface of the flange 120 and to the flange 125 and/or the diaphragm 111 The dish 112 may form an airtight enclosure with the diaphragm 111 and panel 124, but 25 if preferred, holes or perforations my be provided through the dish 112 The internal space within the loudspeaker 110 may include fibrous or foam plastics sound absorbent material The thickness and material of the panel 124 are chosen so that, for example, at frequencies up to 1000 Hz the panel 124 acts as a substantially rigid member and 30 moves the adjacent area ot the diaphragm 111 therewith when alternating current is passed through windings 128 on the voice coil 122 At frequencies above 5000 Hz flexure of the panel 124 is such that the periphery thereof and adjacent areas of the diaphragm J 11 move much less than the voice coil 122 and the central area of the panel 35 124 Thus, at these high frequencies sound is radiated almost entirely from the centre area ol the panel 124 Between those frequencies sound radiation occurs from only a - 14- small area ol the diaphragm 111 and irom parts of the panel 124 In order to modify the ircquency response of the loud speaker 110 at large excursions ot the voice coil 122, the windings 12S may have more turns per unit length towards the ends ol the winding 128 than in the centre thereot This may be achieved by spacing the windings in the centre or by close-winding the turns throughout the length thereot and adding one or more layers 129 adjacent the ends thereof The coils are wound on a ^ tormer 136 provided with perforations 137 It has been iound that a suitable material lor the diaphragms 111 is a double skinned sheet made trom a polypropylene co-polymer approximately 3 millimetres thick and 15 approximately 500 grams per square metre or less Preferably the diaphragm 111 has a tensile strength of around 128 MPa or more and shore haidness of 67 or more The material preferably has a corona discharge treated surface to assist adhesion of paint, wallpaper etc to the diaphragms 111 The diaphragm 111 is preferably a laminate jq having a core ot loam, or has ribs, tubes, corrugated sheet or the like If it has a foam core it preferable that the foam is not uniform (or the cover sheets are shaped or reinforced) For example the foam core could be shaped or reinforced in such a way that the bending stiffness is greater in one direction than another 25 The diaphragm 111 may comprise an integral extrusion ot polyethylene around 3 to 5mm thick and having front and rear skins 130, 131 joined by continuous longitudinal walls 132 with air spaces therebetween By this construction, the material ot the diaphragm 111 is anisotropic and has a longitudinal bending strength which may 30 typically be around twice the transverse bending strength Thus, this material is particularly useful in the construction of rectangular loudspeakers, for example those having sides of 200mm x 100mm long 35 Figure 8 shows the use ot a retaining ring 138, of thin aluminium or the like The ring 138 has a flange 139. which can press down on the external skin 130 of the diaphragm - 15- 111 An integral cylindrical portion 140 can be pushed down between the edge ol the aperture 123 and the outside surlace of the cylindrical part of the panel 124, which has a rib 142 which clicks into a groove 141 in the portion 140 ol the ring 138 The rib 142 and groove 141 may be reversed, it pretcrred ADVANTAGES OF THE PREFERRED EMBODIMENTS: 10 Ease ol manufacture Good acoustics achievable at a low cost ol construction Lightweight diaphragm material particularly suite to rectangular or elliptical panels 15 Scalability Loudspeakers or diaphragms can be made in many dilferent sizes or shapes, or readily disguised as other objects This invention lends itself to flat panel speakers of A5 size or smaller which are 7q particularly suited for the multimedia market, or for inclusion in vehicles titted into dashboards or into vehicle doors The can work in any orientation and depending upon design can be provided with or without a surrounding trame VARIATIONS: 25 One or more drivers may be used depending upon the size ot the diaphragm The loudspeakers may be tuned by porting or by adding weights In the drawings we have show porting in the back panel (figures 6 and 7) but similar porting may be provided in 30 the material of the diaphragm The panels may be tuned by the use of a powder such as sugar or the like on the panel when horizontal so that the nodes can be observed on the panel 35 The diaphragms can be made of any shape (eg they could have irregular outlines if needed) They need not be flat although this is preferred T421JN4J 6'iJ/Jf - 16- Materials other than corc llulc or corrugated cardboard can be used Prelcrably the material is light weight and stilt but llexible In the preferred embodiments standard extruded core llute ol 3mm thickness has been used but other thicknesses between 2mm and 5mm could be used lor most applications Larger panels may require more drivers and a thicker core llute diaphragm The loudspeaker could be disguised as part of a vehicle or part ol lurniture or a box or a ^ painting or almost any object as size or shape is no longer a restriction In one example we have included flat panel loudspeakers as part ol a vehicle dashboard and in another application we have made a painting operate as a loudspeaker. 15 Finally various other alterations or modifications may be made to the foregoing without departing lrom the scope of this invention as set forth m the following claims 20 25 30 35 T-TUHZl </div>

Claims

<div class="application article clearfix printTableText" id="claims"> NOW AMENDED WHAT WE CLAIM IS -17 3 A " l) / V .4' 10 15 20

1. A loudspeaker including a substantially planar first diaphragm/Which can be vibrated so as to radiate sound from at least the front fade thereof, and a driver unit operable by a varying electric current in order to generate y^arying force on the first diaphragm, the force varying in a manner related/to the varying electric current, characterised in that the material of the plany' first ^diaphragm has a bending strength in a single plane along a first axis whicK is greater than along a second axis which is perpendicular to the first axis, and that the driver unit is connected to the first diaphragm at one or more selected positiomror mourned to a structure which is in turn connected to the diaphragm at one or map selected positions.

2. A loudspeaker as claimed ir/claim Y characterised by a substantially rigid peripheral frame having a fronjrface arna a rear face, said first diaphragm extending right across the front face and a reandiaphragm extending right across the rear face whereby the interior spaceyof the lo/dspeaker is substantially enclosed. 25

3. A loudspeaker as claimecfin claim 2, characterised by the driver unit being connected to both of >^aid diaphragms whereby the driver unit will apply varying force,y^orrespoiuiing to the varying electric current, to said diaphragms and cause at le^st one of/said diaphragms to flex and emit an acoustic signal from the face />f the diaphragm exterior of the loudspeaker. 30

4. A loudspeaker as claimed in claim 1, characterised in that said first diaphragm id/or sairear diaphragm is made of double skinned polypropylene copolymer. 35

5. P/ loudspeaker as claimed in claim 1, characterised in that the first diaphragm is maifae of a sheet of extruded plastics material having integral front and rear skins foined by closely spaced parallel walls normal to said skins. T421ICS1.799/JM/iv - WS NOW AMENDED ill / / / 18

6. A loudspeaker as claimed in any preceding claim ctraracterisaa in that the or each diaphragm is approximately 500 grams or less per/Square mefre.

7. A loudspeaker as claimed in any preceding daftn characterised in that the or each diaphragm has a tensile strength of around 28 MPa or m/re. 10

8. A loudspeaker as claimed in any preceding claim Characterised in that the or each diaphragm has a Shore hardness of 67 air more.

9. A loudspeaker as claimed in any /preceding claim characterised in that the surface of the or each diaphragm is treated withya corona discharge to assist adhesion 15 of paint or paper thereto, or of the dia/hragm tc/the frame. 20

10. A loudspeaker as claimed /n any preceding claim characterised in that the driver unit includes two co-a/ial voicor coils, each fastened to a different one of said diaphragms, the X^oice jrails co-acting with a magnet suspended centrally between said voic/coils. 25 30 35

11. A loudspeaker mcluding^i substantially planar diaphragm which can be vibrated so as to radiate sound/from at least the front face thereof, and a driver unit operable by a varying electric cunrent in order to generate a varying force on the diaphragm, the force varying in a ma/ner related to the varying electric current characterised in that the material of the^diaphragm has a bending strength in a single plane along a first axis which is greater than/along a second axis which is perpendicular to the first axis and the diaphragm/s made/of front and rear parallel sheets of material, said sheets being spaced apart by A plurality of walls extending between said sheets and said walls being parallel to eacja other tad extending substantially normal to said sheets, or being of generally rhoijfooidalyOr sinusoidal corrugated form. ""MltlLECTUAL PRKYOFF^ OF N.Z. L 1 T4211CS1.799/JM/iv 2 J JUL 1999 VED NOW AMENDED - 19 -

12. A loudspeaker as claimed in claim 11 characterised in that thandiaphragm is of double skinned polypropylene co-polymer and the wallsy&re substantially normal to said parallel sheets. 10 15

13. A loudspeaker as claimed in claim 11 characterised in/that the diaphragm is of paper or cardboard, said walls being of substantially corrugated form and being fastened by adhesive to the inner opposing faces /f the parjmel sheets.

14. A loudspeaker as claimed in clain/ll in wtfich the driver unit includes a magnet, one pole of which is in magnetic/ontinuitywith a yoke and the other pole of which is positioned from the yoke by /n air gajythrough which gap a voice coil is operable, the voice coil being attached^to drive tpe diaphragm, characterised in that the yoke is made from low oxygen pure iron annealed very slowly in hydrogen. 20

15. A loudspeaker as claimed in claim/14 characterised in that a member made of the same material as the yoke is in magnetic continuity with said other pole of the magnet, the air gap being farmed betvyeen a peripheral portion of said member and an opposing part of the yoke.y 25

16. A loudspeake/as claimara in claim 15 characterised in that said peripheral portion of the member and saiiyopposing part of the yoke are of substantially the same thickness.

17. A loudspeaker ayclaimed in claim 11 characterised in that the voice coil has 30 more windings per uni^ength thereof away from that axial part of the voice coil which is in said gap whe/f no electric current is passed through the windings.

18. /A loudsp/aker as claimed in claim 17 characterised in that the voice coil 35 win/ing is a single layer, with the windings spaced apart in the region of said axial part. T421JNZ3.69//JP NOW AMENDED 20-

19. A loudspeaker as claimed in claim 17 characterised in/hat more than said single layer is wound at regions of the voice coil further from said /xial part. 10 15

20. A loudspeaker as claimed in claim li characterised in that the voice coil of the driver unit is connected to said diaphragm/by meanspf a panel of material, said panel being of a material and having dimensions suom that at a low range of audio frequencies, the voice coil and at lea/t that part/f the diaphragm adjacent the panel move substantially at the same amplitude and pKase, while at a higher range of audio frequencies at least said part of tho'diaphragimuid a part of the panel adjacent thereto move at a lower amplitude and/or at a differ/nt phase from the voice coil, whereby at said higher range a substantial part of the s/und emitted by the loudspeaker is radiated from a face of the panel adjac/nt the voicercoil. 20

21. A loudspeaker as /laimed in cjaim 11 characterised in that a sheet of damping material is connected firom a stati/nary part of the loudspeaker to said part of the diaphragm adjacent tne panel or/o the panel and in which the damping material is porous or perforated/o as to allow the passage of air therethrough. 25 30 35

22. A loudsp/aker as clai/ned in claim 21 characterised in that the damping material is cloth or clothrbased.

22. A loudspeaker substantially as herein described with reference to any one of the acoompanying drawings. SLAB TECHN BV its Attorn *IPERS INT^cmrmPERfY of n.z. office I T421JNZ3.699/JP 2 I J UN (599 jjECEM/Fn AS AMENDED WHAT WE CLAIM IS 1 A loudspeaker including a substantially planar first diaphragm which can be vibrated so as to radiate sound from at least the front face thereof, and a driver unit operable by a varying electric current in order to generate a varying force on the first diaphragm, the force varying in a manner related to the varying electric current, characterised in that the material of the planar first diaphragm has a bending strength in a single plane along a first axis which is greater than along a second axis which is perpendicular to the first axis, and that the driver unit is connected to the first diaphragm at one or more selected positions or mounted to a structure which is in turn connected to the diaphragm at one or more selected positions 2 A loudspeaker as claimed in claim 1 characterised by a substantially rigid peripheral frame having a front face and a rear face, said first diaphragm extending right across the front face and a rear diaphragm extending right across the rear face whereby the interior space of the loudspeaker is substantially enclosed 3 A loudspeaker as claimed in claim 2, characterised by the driver unit being connected to both of said diaphragms whereby the driver unit will apply varying force, corresponding to the varying electric current, to said diaphragms and cause at least one of said diaphragms to flex and emit an acoustic signal from the face of the diaphragm exterior of the loudspeaker 4 A loudspeaker as claimed in claim 1, characterised in that said first diaphragm and/or said rear diaphragm is made of double skinned polypropylene copolymer 5 A loudspeaker as claimed in claim 1, characterised in that the first diaphragm is made of a sheet of extruded plastics material having integral front and rear skins joined by closely spaced parallel walls normal to said skins

6. A loudspeaker as claimed in any preceding claim characterised in that the or each diaphragm is approximately 500 grams or less per square metre AS AMENDED 7 A loudspeaker as claimed in any preceding claim characterised in that the or each diaphragm has a tensile strength of around 28 MPa or more. 8 A loudspeaker as claimed in any preceding claim characterised in that the or each diaphragm has a Shore hardness of 67 or more 9 A loudspeaker as claimed in any preceding claim characterised in that the surface of the or each diaphragm is treated with a corona discharge to assist adhesion of paint or paper thereto, or of the diaphragm to the frame 10 A loudspeaker as claimed in any preceding claim characterised in that the driver unit includes two co-axial voice coils, each fastened to a different one of said diaphragms, the voice coils co-acting with a magnet suspended centrally between said voice coils 11 A loudspeaker including a substantially planar diaphragm which can be vibrated so as to radiate sound from at least the front face thereof, and a driver unit operable by a varying electric current in order to generate a varying force on the diaphragm, the force varying in a manner related to the varying electric current characterised in that the material of the diaphragm has a bending strength in a single plane along a first axis which is greater than along a second axis which is perpendicular to the first axis and the diaphragm is made of front and rear parallel sheets of material, said sheets being spaced apart by a plurality of walls extending between said sheets and said walls being parallel to each other and extending substantially normal to said sheets, or being of generally rhomboidal or sinusoidal corrugated form 12 A loudspeaker as claimed in claim 11 characterised in that the diaphragm is of double skinned polypropylene co-polymer and the walls are substantially normal to said parallel sheets. 13 A loudspeaker as claimed in claim 11 characterised in that the diaphragm is of paper or cardboard, said walls being of substantially corrugated form and being fastened by adhesive to the inner opposing faces of the parallel sheets AS AMENDED 14 A loudspeaker as claimed in claim 11 in which the driver unit includes a magnet, one pole of which is in magnetic continuity with a yoke and the other pole of which is positioned from the yoke by an air gap through which gap a voice coil is operable, the voice coil being attached to drive the diaphragm, characterised in that the yoke is made from low oxygen pure iron annealed very slowly in hydrogen 15 A loudspeaker as claimed in claim 14 characterised in that a member made of the same material as the yoke is in magnetic continuity with said other pole of the magnet, the air gap being formed between a peripheral portion of said member and an opposing part of the yoke 16 A loudspeaker as claimed in claim 15 characterised in that said peripheral portion of the member and said opposing part of the yoke are of substantially the same thickness 17 A loudspeaker as claimed in claim 11 characterised in that the voice coil has more windings per unit length thereof away from that axial part of the voice coil which is in said air gap when no electric current is passed through the windings 18 A loudspeaker as claimed in claim 17 characterised in that the voice coil winding is a single layer, with the windings spaced apart in the region of said axial part.

19. A loudspeaker as claimed in claim 17 characterised in that more than said single layer is wound at regions of the voice coil further from said axial part. 20 A loudspeaker as claimed in claim 11 characterised in that the voice coil of the driver unit is connected to said diaphragm, by means of a panel of material, said panel being of a material and having dimensions such that at a low range of audio frequencies, the voice coil and at least that part of the diaphragm adjacent the panel move substantially at the same amplitude and phase, while at a higher range of audio frequencies at least said part of the diaphragm and a part of the panel adjacent thereto move at a lower amplitude and/or at a different phase from the voice coil, whereby at said higher range a substantial part of the sound emitted by the loudspeaker is radiated AS AMENDED from a face of the panel adjacent the voice coil 21 A loudspeaker as claimed in claim 11 characterised in that a sheet of damping material is connected from a stationary part of the loudspeaker to said part of the diaphragm adjacent the panel or to the panel and in which the damping material is porous or perforated so as to allow the passage of air therethrough. 22 A loudspeaker as claimed in claim 21 characterised in that the damping material is cloth or cloth based 23 A loudspeaker as claimed in claim 11 characterised in that said walls are of substantially corrugated form and extend parallel to said sheets. 24 A loudspeaker as claimed in claim 23 characterised in that the diaphragm is of paper or cardboard fastened by adhesive to the inner opposing faces of the parallel sheets. 25 A loudspeaker as claimed in claim 24 characterised in that the corrugations are of sinusoidal form. 26 A loudspeaker substantially as herein described with reference to any one of the accompanying drawings. </div>