Abstract
An ironless magnet assembly (128) for a loudspeaker (101) comprising two pairs of magnets (136) is disclosed. Each magnet (136) of each pair having a north pole and a south pole, a first pair of magnets (136c, 136d) are arranged with the north poles of the magnets of that pair facing each other and a second pair of magnets (136a, 136b) are arranged with the south poles of the magnets of that pair facing each other. The first pair of magnets (136c, 136d) are located opposite the second pair of magnets (136a, 136b) to define a voice coil gap (112) therebetween with each north pole of the first pair being located opposite a south pole of the second pair across the voice coil gap (112).
Claims
1. An ironless magnet assembly for a loudspeaker comprising two pairs of magnets, each magnet of each pair having a north pole and a south pole, a first pair of magnets being arranged with the north poles of the magnets of that pair facing each other and a second pair of magnets being arranged with the south poles of the magnets of that pair facing each other; the first pair of magnets being located opposite the second pair of magnets to define a voice coil gap therebetween with each north pole of the first pair being located opposite a south pole of the second pair across the voice coil gap.
2. A magnet assembly according to claim 1, wherein the width of the voice coil gap defined between the two pairs of magnets varies along the length of the voice coil gap.
3. A magnet assembly according to claim 2, wherein each magnet comprises a first surface that is neither parallel nor perpendicular to a longitudinal axis of the voice coil gap, the first surfaces of the magnets together defining an enlarged region of the voice coil gap.
4. A magnet assembly according to claim 3, wherein for each magnet, a first notional plane may be defined that faces the opposing magnet of the other pair; and a second notional plane may be defined that faces the other magnet of the pair; and the first surface extends between the first and second notional planes thereby defining the enlarged region of the voice coil gap.
5. A magnet assembly according to claim 4, wherein at least one of the magnets has a polygonal shape when viewed in cross-section and the first and/or second notional plane is coincident with a first and/or second side of the magnet respectively.
6. A magnet assembly according to claim 3, wherein the cross-sectional shape of the first surface is defined by a line comprising one or more straight portions and/or one or more curved portions.
7. A magnet assembly according to claim 6, wherein the majority of the length of the line is substantially straight, for example wherein each magnet comprises a chamfered corner.
8. A magnet assembly according to claim 1, wherein one of the first or second pair of magnets is concentrically located within the other of the first or second pair of magnets.
9. A magnet assembly according to claim 1, wherein each magnet is a permanent magnet, for example a magnet comprising Neodymium (NdFeB), Samarium-cobalt (SmCo), and/or hard ferrites, for example ceramic materials, for example Strontium ferrite (SrFeO) and/or Barium ferrite (BaFeO).
10. A magnet assembly according to claim 1, wherein a spacer is located between the magnets of the first pair and/or the second pair.
11. A magnet assembly according to claim 10, wherein the or each spacer comprises thermally conductive material such that the spacer conducts heat away from the magnets.
12. A magnet assembly according to claim 11, wherein the or each spacer is in thermal communication with a heat sink.
13. A drive unit including a magnet assembly in accordance with claim 1, the drive unit comprising a diaphragm connected to a voice coil located in the voice coil gap.
14. A loudspeaker including a magnet assembly in accordance with claim 1.
15. A method of manufacturing an ironless magnet assembly for a loudspeaker, the method comprising: arranging a plurality of magnets to provide a first pair of magnets wherein the force generated between the poles of the magnets acts to repel the magnets from each other; a second pair of magnets where the force generated between the poles of the magnets acts to repel the magnets from each other; and wherein the first and second pair of magnets define a voice coil gap therebetween so that the force generated between the poles of the first and second pairs acts to attract the magnets to each other.
16. A method according to claim 15, wherein the step of arranging the second pair of magnets comprises placing the magnets of the second pair either side of a spacer.
17. A method according to claim 15, wherein the step(s) of arranging the first and/or second pair of magnets comprises bonding the magnets together, for example using an adhesive.
18. A method according to claim 15, wherein the method comprises shaping each magnet to provide a first surface and arranging each magnet such that the first surfaces of the magnets together define an enlarged region of the voice coil gap.
19. A method according to claim 18, wherein the step of shaping each magnet comprises sintering, for example laser sintering, a powder to form a magnet.
20. A method according to claim 18, wherein the step of shaping each magnet comprises removing material from a magnet to produce a first surface.
21. A magnet assembly for a loudspeaker comprising two pairs of magnets, each magnet of each pair having a north pole and a south pole, a first pair of magnets being arranged with the north poles of the magnets of that pair facing each other and a second pair of magnets being arranged with the south poles of the magnets of that pair facing each other; the first pair of magnets being located opposite the second pair of magnets to define a voice coil gap therebetween with each north pole of the first pair being located opposite a south pole of the second pair across the voice coil gap; each magnet comprises a first surface that is neither parallel nor perpendicular to a longitudinal axis of the voice coil gap, the first surfaces of the magnets together defining an enlarged region of the voice coil gap; and wherein for each magnet, a first notional plane may be defined that faces the opposing magnet of the other pair; and a second notional plane may be defined that faces the other magnet of the pair; and the first surface extends between the first and second notional planes thereby defining the enlarged region of the voice coil gap.
22. (canceled)
23. A loudspeaker including a drive unit in accordance with claim 13.
Description
DESCRIPTION OF THE DRAWINGS
[0069] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which:
[0070] FIG. 1 shows a cross-sectional view of a conventional loudspeaker;
[0071] FIG. 2 shows a cross-sectional perspective view of part of a drive unit according to a first example embodiment of the invention;
[0072] FIG. 3 shows a close up view of part of the magnet assembly of FIG. 2;
[0073] FIG. 4 shows flux lines in the magnet assembly of FIG. 2;
[0074] FIG. 5 shows a close up view of part of a magnet assembly in accordance with a second example embodiment of the invention;
[0075] FIG. 6 shows flux lines in part of a magnet assembly in accordance with a third example embodiment of the invention;
[0076] FIG. 7 shows a close up of part the magnet assembly of FIG. 6; and
[0077] FIG. 8 shows an example method of manufacturing a magnet assembly.
DETAILED DESCRIPTION
[0078] FIG. 2 shows a cross-sectional view of part of a loudspeaker assembly 101 in accordance with a first example embodiment of the invention. Elements that are similar as between FIGS. 1 and FIG. 2 have been indicated in FIG. 2 using their reference numeral from FIG. 1 incremented by 100 (i.e. spider 20 in FIG. 1 is referred to as spider 120 in FIG. 2). FIG. 2 shows a diaphragm 102, connected to a half roll surround 106. For clarity, the chassis has been omitted from FIG. 2, but it will be understood that the outer perimeter of the surround 106 would be connected to the chassis. A dust cap 122 is located at the centre of the diaphragm 102. A voice coil 110 comprising a cylindrical voice coil former 130 having a coil 132 (see FIG. 3) wound around it extends downwardly from the centre of the diaphragm 102 in a voice coil gap 112 formed between four magnets 136. Two of the magnets, labelled 136a, 136b in FIG. 3 are annular and form a pair with an upper annular magnet 136a being located on top of a lower annular magnet 136b. Two of the magnets, labelled 136c, 136d in FIG. 3 are conical and form a paid with an upper conical magnet 136c being located on top of a lower conical magnet 136d. The conical magnets 136c, 136d are concentrically located within the annular magnets 136a, 136b, the voice gap 112 being the annular gap formed between them. A spider 120 in the form of a corrugated disk extends from the voice coil former 130 to the chassis (not shown). It will be appreciated that the present invention is concerned with the arrangement of the magnets 136 and the shape and configuration of other elements of the loudspeaker, e.g. the shape and configuration of the diaphragm 102, support 106, voice coil 110 and/or spider 120, may differ from that shown here. Additionally or alternatively, some elements shown here, for example dust cap 122 may be absent in other embodiments of the present invention. Magnets 136 are Neodymium (NdFeB) magnets produced by laser sintering material in powdered form and then grinding to shape and form magnet assembly 128. The drive unit of FIG. 2 is an ironless drive unit—there are no soft magnetic materials arranged to control the flux of the magnetic field. In other embodiments NdFeB magnets produced by other manufacturing processes may be used. In yet further embodiments, the magnets may be made of any permanent magnet material, for example Samarium-cobalt (SmCo), and/or hard ferrites, for example ceramic materials, for example Strontium ferrite (SrFeO) and/or Barium ferrite (BaFeO). In yet further embodiments, the drive unit may be non-ironless, for example ferromagnetic materials, for example iron or steel may be used for the magnets. The pairs of magnets 136a, 136b and 136c, 136d are directly bonded together using an adhesive.
[0079] FIG. 3 shows a cross-sectional close up of part of the loudspeaker assembly of FIG. 2. The line of symmetry of the loudspeaker assembly of FIG. 2 is indicated by a dashed line labelled A in FIG. 3. The north and south poles of each magnet are indicated with an N or S respectively in FIG. 3. As shown in FIG. 2, the two conical magnets 136c, 136d are arranged with their north poles immediately adjacent to and facing each other. The two annular magnets 136a, 136b are arranged with their south poles immediately adjacent to and facing each other. In other embodiments, the polarities may be reversed, i.e. the south poles of the conical magnets 136c, 136d facing each other and the north poles of the annular magnets 136a, 136b facing each other. The conical magnets 136c, 136d are located opposite the annular magnets 136a, 136b such that each south pole of an annular magnet 136a, 136b is vertically aligned with a south pole of a conical magnet 136c, 136d. A first side 142 of each magnet faces the voice gap 112. A second side 144 of each magnet faces the other magnet 136 of the same type (i.e. conical or annular). The first side 142 is approximately perpendicular to the second side 144. The first side 142 and second side 144 are joined by a third, straight, side 146 extending between them; thus the corner between the first side 142 and second side 144 may be said to be chamfered. The chamfering creates an enlarged region 112a of the voice coil gap 112. The voice coil 110 is located in this enlarged region 112a in FIG. 3. The first side 142 and third side 144 of a magnet 136 may be said to form a surface defining at least a portion of the voice coil gap 112. In other embodiments, the third side 146 may not be straight and/or diagonal, for example in some embodiments the third side 146 may be curved or have a complex geometry. A notional circle, denoted by dashed line B in FIG. 3, is shown in the enlarged region 112a of the voice coil gap 112. The radius of the notional circle B is more than twice the maximum distance moved by the voice coil 110 during normal operation—that is the longitudinal distance between the point foremost (or uppermost as shown in FIG. 3) and rearmost (of lowest as shown in FIG. 3) point of travel of the coil 132 during normal operation.
[0080] A copper sleeve 148 extends along one side of the voice coil gap 112 from the first side 142 of the upper conical magnet 136c to the first side 142 of the lower conical magnet 136d.
[0081] FIG. 4 shows flux lines in and around the magnets 136 of FIG. 3. In the enlarged region 112a of the voice coil gap 112 the flux lines are fairly evenly spaced and substantially perpendicular to the axis of movement of the voice coil 110. Consequently, the magnetic field density is substantially constant in the enlarged region 112a. Accordingly, loudspeakers in accordance with the present example embodiment may provide improved sound reproduction as a consequence of reduced nonlinearity in the force experienced by the voice coil as it moves in the voice coil gap. Additionally or alternatively, use of the shaped e.g. chamfered edges in accordance with the present example embodiment allows a designer to shape the magnetic flux in the air gap to obtain a desired force factor behaviour. Additionally or alternatively, use of the shaped e.g. chamfered edges in accordance with the present embodiment may allow for a reduction in the size of magnets required allowing for a reduction in loudspeaker size and/or weight.
[0082] FIG. 5 shows a cross-sectional close up of part of a loudspeaker assembly in accordance with a second example embodiment. Elements that are similar as between FIGS. 3 and FIG. 5 have been indicated in FIG. 5 using their reference numeral from FIG. 3 incremented by 100 (i.e. magnet 136 in FIG. 3 is referred to as magnet 236 in FIG. 5). The arrangement of FIG. 5 is substantially as described in FIG. 3, with the exception that a spacer plate 250 is located in between the two annular magnets 236a, 236b. The inner end 250a of the spacer plate 250 (the end adjacent the voice coil gap 212) comprises projections 252 that fill the space created by the chamfered corners of the annular magnets 236a, 236b so that together the surfaces of the annular magnets 236a, 236b and distal end 250a facing the voice coil gap 212 form a straight line. Spacer plate 250 extends radially outward to an upwardly extending wall 253 that along with pole plate 226 forms a cup 254 around the magnets 236. Conical magnets 236c, 236d are mounted on pole plate 226. Spacer plate 250, wall 252 and pole plate 226 are made from Aluminium. Accordingly, the loudspeaker assembly of the second example embodiment may be described as an ‘ironless’ loudspeaker. In other embodiments, different material may be used. However, use of materials having a magnetic permeability similar to that of the fluid in the voice coil gap (for example Air) may reduce the impact of the cup on the magnetic field.
[0083] Spacer plate 250 conducts heat away from magnets 236, accordingly loudspeakers in accordance with the present embodiment may have improved heat dissipation. Heat from spacer plate 250 may be dissipated by airflow over cup 254. Additionally or alternatively, loudspeakers in accordance with the present embodiment may be easier to manufacture as spacer plate 250 provides an increased gluing area and facilitates arranging the magnets 236 with like poles adjacent (i.e. in a configuration in which the magnets 236 repel each other).
[0084] In other embodiments, not shown, a spacer plate may be provided between the two conical magnets. This may be in addition to or instead of the spacer plate provided between the two annular magnets.
[0085] FIG. 6 shows flux lines in and around the magnets 336 of a loudspeaker in accordance with a third example embodiment. Elements that are similar as between FIG. 5 and FIG. 6 have been indicated in FIG. 6 using their reference numeral from FIG. 5 incremented by 100 (i.e. magnet 236 in FIG. 5 is referred to as magnet 336 in FIG. 6). A spacer plate (not shown in FIG. 6) is located between each pair of magnets 336. In the third example embodiment the shape of the magnets 336 is more complex in comparison to the straight-line geometry of the previous embodiments. Away from the location of the voice coil 310 as shown in FIG. 6 the inner pair of magnets 336c, 336c are substantially rectangular when viewed in cross-section with a first side 342 facing the voice coil gap 112/outer pair of magnets 336a, 336b and a second side 344 facing the other magnet of the pair (i.e. the other inner magnet 336c or 336d). However, the surface 346 extending between the first side 342 and the second side 344 comprises, when viewed in cross-section, in order from the second side 344 to the first side 342, a first curve 346a, a corner 346b, a straight portion 346c and a second curve 346d (shown in more detail in FIG. 7). The inner pair of magnets 336c, 336d are symmetrical about a horizontal plane. Away from the location of the voice coil 310 as shown in FIG. 6 the outer pair of magnets 336a, 336b are substantially oval when viewed in cross-section with a the first side 342 being a notional first side 342 facing the voice coil gap 112/inner pair of magnets 336c, 336d and a second side 344 being a notional second side 344 facing the other magnet of the pair (i.e. the other outer magnet 336a or 336b). Notional first side 342 and second side 344 of the outer pair of magnets 336a, 336b are shown by dashed lines in FIG. 6. The surface 346 extending between the first side 342 and the second side 344 of each magnet 336a, 336b of the outer pair, when viewed in cross-section, in order from the second side 344 to the first side 342, a first curve 346a, a corner 346b, a straight portion 346c and a second curve 346d. However the radius and length of the curves differs as between the inner magnets 336c, 336d and the outer pair of magnets 336a, 336b, giving a different profile for two pairs of magnets. The outer pair of magnets 336a, 336b are symmetrical about a horizontal plane. A first enlarged region 112a of the voice coil gap 112 is defined by the first curves 346a of the magnets 336. Second 112b and third 112c enlarged regions of the voice coil gap are defined by the second curves 346d of the magnets 336 and are located either side of the first enlarged region 112a along the length of the voice coil gap 112. The voice coil gap 112 is symmetrical about a horizontal plane. The Neodymium magnets 336 are mounted on spacer plates and supporting structure (not shown in FIG. 6) made of Aluminium using adhesive. In other embodiments, different materials may be used for the magnets, space plates and/or supporting structure.
[0086] In and between the three enlarged regions 312a of the voice coil gap 312 the flux lines are fairly evenly spaced and substantially perpendicular to the axis of movement of the voice coil 310. Consequently, the magnetic field density is substantially constant in the portion of the voice coil gap 312 occupied by the voice coil 310 during normal operation. Accordingly, loudspeakers in accordance with the present example embodiment may provide improved sound reproduction as a consequence of reduced nonlinearity in the force experienced by the voice coil as it moves in the voice coil gap. Additionally or alternatively, use of the shaped edges in accordance with the present example embodiment allows a designer to shape the magnetic flux in the air gap to obtain a desired force factor behaviour. Additionally or alternatively, use of the shaped e edges in accordance with the present embodiment may allow for a reduction in the amount of magnetic material required to achieve a particular magnetic flux profile thereby allowing for a reduction in loudspeaker size, weight and/or cost.
[0087] FIG. 8 shows a flow chart of an example method of manufacturing a magnet assembly in accordance with the present invention. The method comprises building up 60 each permanent magnet by laser sintering a powdered material. The method comprises grinding 62 each magnet to produce a chamfered edge, as described above. In other embodiments other additive manufacturing processes may be used in isolation or in combination with subtracting manufacturing processes to produce magnets as described in any of the above example embodiments. The method comprises bonding 64 the north poles of a first pair of magnets together using an adhesive. The method comprises bonding 66 the south poles of a second pair of magnets together using an adhesive. In other embodiments the magnets may not be directly bonded together, but may instead be bonded and/or otherwise mounted to a support structure. The method may comprise arranging 68 the first pair of magnets opposite the second pair of magnets to provide a voice coil gap, with each north pole opposing a south pole across the gap.
[0088] In some embodiments, the method may comprise providing 70 an original design for a drive unit. The method may comprise modifying 72 the shape of the first surface of the magnets of the original design to provide a target magnetic field in the voice coil gap. The method may then comprise making 74 a magnet to the modified design that method optionally including the steps discussed above.
[0089] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein.
[0090] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.
