Abstract
A loudspeaker including a chassis, a drive unit and a diaphragm. The drive unit has a stationary part secured to the chassis and a translatable part secured to the diaphragm. An outer edge of the diaphragm is suspended from the chassis by an edge suspension. The edge suspension has a plurality of straight portions, each straight portion having a respective first surface and a respective second surface which meet along an edge to provide a spring which permits the diaphragm to be moved relative to the chassis by the drive unit. The edge suspension has at least one corner portion, wherein the/each corner portion joins two of the straight portions together and includes at least one geometrical interruption formed therein.
Claims
1. A loudspeaker including a chassis, a drive unit and a diaphragm; wherein the drive unit has a stationary part secured to the chassis and a translatable part secured to the diaphragm; wherein an outer edge of the diaphragm is suspended from the chassis by an edge suspension; wherein the edge suspension has a plurality of straight portions, each straight portion having a respective first surface and a respective second surface which meet along an edge to provide a spring which permits the diaphragm to be moved relative to the chassis by the drive unit; wherein the edge suspension has at least one corner portion, wherein the/each corner portion joins two of the straight portions together and includes at least one geometrical interruption formed therein; wherein the/each geometrical interruption formed in the/each corner portion includes a first corrugation which varies in height along a first path which extends circumferentially around the edge suspension, and a second corrugation formed within the first corrugation which varies in height along a second path which extends across the first path; wherein each straight portion includes one or more stiffening elements; wherein the one or more stiffening elements include one or more geometrical interruptions formed in each straight portion; wherein the/each geometrical interruption formed in each straight portion includes a first corrugation which varies in height along a first path which extends circumferentially around the edge suspension, and a second corrugation formed within the first corrugation which varies in height along a second path which extends across the first path.
2. A loudspeaker according to claim 1, wherein the edge suspension is the only suspension element by which the diaphragm is suspended from the chassis.
3. A loudspeaker according to claim 1, wherein the one or more stiffening elements included in each straight portion further includes: one or more ridges on the first surface and/or on the second surface of each straight portion; and/or one or more one planar sheets of material attached to the first surface and/or to the second surface of each straight portion.
4. A loudspeaker according to claim 1, wherein the/each corner portion has a first surface and a second surface which meet along a curved edge.
5. A loudspeaker according to claim 4, wherein the edge of the/each corner portion is a non-continuous edge including a plurality of edge segments with the edge segments being separated by the at least one geometrical interruption formed in the corner portion.
6. A loudspeaker according to claim 5, wherein the non-continuous edge of the/each corner portion includes a plurality of edge segments with the edge segments being separated by at least three geometrical interruptions formed in the corner portion.
7. A loudspeaker according to claim 6, wherein: the non-continuous edge of the/each corner portion includes a plurality of edge segments separated by three geometrical interruptions formed in the corner portion, wherein the three geometrical interruptions include an inner geometrical interruption located between two outer geometrical interruptions; for the/each corner portion, the inner geometrical interruption has a width and height that are smaller than the corresponding width and height of both of the outer geometrical interruptions.
8. A loudspeaker according to claim 1, wherein: the first corrugation included in the/each geometrical interruption is a valley, wherein the valley is concave with respect to a front side of the edge suspension; the second corrugation formed within each first corrugation is a hill, wherein the hill is convex with respect to the valley in which it is formed; the first corrugation included in the/each geometrical interruption is a U shaped valley; the second corrugation formed within each first corrugation is an inverted U shaped hill.
9. A loudspeaker according to claim 8, wherein the distance by which each hill extends into the mouth of the valley in which it is formed is less than half the depth of the valley in which it is formed.
10. A loudspeaker according to claim 1, wherein: the/each corner portion provides a continuous seal between the diaphragm and the chassis; the entire edge suspension provides a continuous seal between the diaphragm and the chassis.
11. A loudspeaker according to claim 1, wherein the/each corner portion is made from the same material as and integrally formed with the straight portions, wherein the material is a textile material, or a paper material.
12. A loudspeaker according to claim 1, wherein the edge suspension has a plurality of corner portions, wherein each corner portion joins two of the straight portions together and includes at least one geometrical interruption formed therein.
13. A loudspeaker according to claim 1, wherein: the edge suspension comprises four straight portions and four corner portions to form a square/rectangular shape; and/or the diaphragm includes a dome or a cone shape portion.
14. A passive radiator that includes a chassis and a diaphragm; wherein an outer edge of the diaphragm is suspended from the chassis by an edge suspension; wherein the edge suspension has a plurality of straight portions, each straight portion having a respective first surface and a respective second surface which meet along an edge to provide a spring which permits the diaphragm to be moved relative to the chassis; wherein the edge suspension has at least one corner portion, wherein the/each corner portion joins two of the straight portions together and includes at least one geometrical interruption formed therein; wherein the/each geometrical interruption formed in the/each corner portion includes a first corrugation which varies in height along a first path which extends circumferentially around the edge suspension, and a second corrugation formed within the first corrugation which varies in height along a second path which extends across the first path; wherein each straight portion includes one or more stiffening elements; wherein the one or more stiffening elements include one or more geometrical interruptions formed in each straight portion; wherein the/each geometrical interruption formed in each straight portion includes a first corrugation which varies in height along a first path which extends circumferentially around the edge suspension, and a second corrugation formed within the first corrugation which varies in height along a second path which extends across the first path.
15. An edge suspension for suspending an outer edge of a diaphragm from a chassis in a loudspeaker; wherein the edge suspension has a plurality of straight portions, each straight portion having a respective first surface and a respective second surface which meet along an edge to provide a spring for permitting the diaphragm to be moved relative to the chassis by a drive unit of the loudspeaker; wherein the edge suspension has at least one corner portion, wherein the/each corner portion joins two of the straight portions together and includes at least one geometrical interruption formed therein; wherein the/each geometrical interruption formed in the/each corner portion includes a first corrugation which varies in height along a first path which extends circumferentially around the edge suspension, and a second corrugation formed within the first corrugation which varies in height along a second path which extends across the first path; wherein each straight portion includes one or more stiffening elements; wherein the one or more stiffening elements include one or more geometrical interruptions formed in each straight portion; wherein the/each geometrical interruption formed in each straight portion includes a first corrugation which varies in height along a first path which extends circumferentially around the edge suspension, and a second corrugation formed within the first corrugation which varies in height along a second path which extends across the first path.
16. A loudspeaker according to claim 8, wherein the hill is contained entirely within the valley in which it is formed.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) Examples of these proposals are discussed below, with reference to the accompanying drawings in which:
(2) FIG. 1 shows a cross-sectional view of an electro-dynamic loudspeaker having a conventional design.
(3) FIG. 2 shows a cross-sectional view of an electro-dynamic loudspeaker according to the present invention.
(4) FIG. 3(a) shows two adjacent blade springs of the loudspeaker of FIG. 2 when the voice coil is moved in the coil in direction.
(5) FIG. 3(b) shows the same two adjacent blade springs of the loudspeaker of FIG. 2 when the voice coil is moved in the coil out direction.
(6) FIG. 4 shows a 3-dimensional (3D) representation of the trajectories of the edges of the two blade springs shown in FIGS. 3(a) and 3(b).
(7) FIG. 5 shows a 2-dimensional (2D) projection of the 3D trajectories shown in FIG. 4.
(8) FIG. 6 shows elongation of a distance between glue surfaces on a blade spring of the loudspeaker of FIG. 2 when the diaphragm is moved in the coil in and coil out directions.
(9) FIG. 7 shows an example corner portion for joining two blade springs, wherein three geometrical interruptions are formed in the corner portion.
(10) FIG. 8 shows two blade springs which are not joined by a corner portion.
(11) FIG. 9 shows an example corner portion for joining two blade springs, wherein no geometrical interruptions are formed in the corner portion.
(12) FIG. 10 shows an example corner portion for joining two blade springs, wherein three geometrical interruptions that include only top surface interruptions are formed in the corner portion.
(13) FIG. 11 shows two curves to represent the restoring provided by the edge suspension of FIG. 2 relative to displacement of the diaphragm (i) when corner portions are omitted from the edge suspension (lower curve); (ii) when corner portions as shown in FIG. 7 are present (upper curve).
(14) FIG. 12 shows an edge suspension with stiffening elements on the straight portions in the form of cylindrical ridges.
(15) FIG. 13 shows an edge suspension with stiffening elements on the straight portions in the form of geometrical interruptions.
(16) FIG. 14 shows an edge suspension with stiffening elements on the straight portions in the form of planar stiffening elements.
(17) FIGS. 15(a) and (b) shows a suspension element and a diaphragm having an inverted cone portion.
(18) FIG. 16 shows a suspension element and a diaphragm having a cone portion.
(19) FIG. 17 shows a suspension element and a diaphragm including a dome.
DETAILED DESCRIPTION
(20) When blade springs and their hinge mechanisms are examined, it can be observed that their movement is very complex, especially at the sides.
(21) As shown by FIG. 4 of U.S. Pat. No. 4,056,697 and FIG. 3 of U.S. Pat. No. 6,385,327 B1, it can be seen that blade springs deform as a diaphragm travels along a symmetry axis of a loudspeaker. In addition, the hinge mechanism joining the surfaces of the blade springs moves in a direction which is perpendicular to the symmetry axis of the loudspeaker.
(22) FIG. 2 shows an example loudspeaker 100 that includes a chassis 105, a drive unit and a diaphragm 103.
(23) The drive unit has a stationary part secured to the chassis 105 and a translatable part secured to the diaphragm 103.
(24) The translatable part of the drive unit includes a voice coil 102a coupled to the diaphragm 103 via a voice coil former 102b around which the voice coil 102a is wrapped. The stationary part of the drive unit includes metal components 101a and a permanent magnet 101b. The voice coil 102a and voice coil former together form the translatable part of the drive unit. The metal components 101a and permanent magnet 101b together form the stationary part of the drive unit.
(25) An outer edge of the diaphragm is suspended from the chassis by an edge suspension 104 that has a plurality of straight portions 140 and a plurality of corner portions 150, wherein each corner portion 150 (respectively) joins two of the straight portions 140 together and (respectively) includes at least one geometrical interruption formed therein. The corner portions 150 are not visible in FIG. 2, but can be seen in FIG. 7 (discussed below).
(26) Each straight portion has a respective first surface 141a and a respective second surface 141b, which meet along an edge 142 which extends between two of the corner portions to provide a blade spring 140 which permits the diaphragm 103 to be moved along a predetermined axis 108 relative to the chassis 105 by the drive unit. The straight portions 140 are referred to as blade springs 140 herein.
(27) Although FIG. 2 depicts a loudspeaker 100, it would be possible to instead provide a passive radiator by omitting the drive unit (i.e. by omitting the metal components 101a, permanent magnet 101b, voice coil 102a and voice coil former 102b) from the loudspeaker of FIG. 2. A passive radiator (also passive slave or drone cone) is a component typically used to tune the frequency response in a loudspeaker enclosure. The possibility of a passive radiator will not be discussed further herein, though a skilled person would appreciate that many of the features described in relation to the loudspeaker 100 could equally be applied to a passive radiator in which the drive unit is omitted.
(28) As shown by FIGS. 3(a) and 3(b), when the loudspeaker 100 of FIG. 2 is in use, the following deformations can be observed in adjacent blade springs 140: 1. When the voice coil 102a moves in a coil in direction (i.e. towards the permanent magnet 101b), the edges 142 of the blade springs 140 (which can be viewed as the tips of a triangle formed by each blade spring 140, when viewed in cross section) move closer to each other, as shown in FIG. 3(a); and 2. When the voice coil 102a moves in a coil out direction (i.e. away from the permanent magnet 101b), the edges 142 of the blade springs 140 move away from (i.e. separate from) each other, as shown in FIG. 3(b).
(29) Note that since the voice coil 102a is secured to the diaphragm 103 of the loudspeaker 100, the coil in and coil out directions can also be used to describe a direction of movement of the diaphragm 103.
(30) From FIGS. 3(a) and 3(b) it can be seen that the edges 142 of the adjacent blade springs 140 are moving relative to each other along an axis which is perpendicular to the symmetry axis 108 of the diaphragm 103. More accurately, when the trajectories of the edges 142 are observed, it can be seen that they are following an arc shaped line in 3-dimensional space, as shown in FIG. 4. These two arcs that are formed with the two edges 142 of two adjacent blade springs 140 get closer when the diaphragm moves in the coil in direction and they get further apart from each other when the diaphragm moves in the coil out direction.
(31) The fact that the edges 142 of the blade springs 140 of FIGS. 3(a) and 3(b) are in relative movement towards and away from each other when the loudspeaker 100 is in use suggests to the present inventors that any construction placed in between these two blade springs 140 to establish sealing between the front and the back sides of the diaphragm should permit this relative movement in order not to degrade the linearity of the suspension provided by the edge suspension 104.
(32) In FIG. 4, the dotted curves represent the movement of the edges 142 of the respective blade springs 140. A basic drawing of the cross-section of the blade springs 140 has been added to the graph of FIG. 4 to indicate the rest position of the springs.
(33) FIG. 4 illustrates that, when blade springs 140 are positioned to form a 90-degrees angle between them, the planes in which the trajectories of the edges 142 are contained are perpendicular to each other. In more detail, the trajectory of the edge 142 shown on the left of FIG. 4 is contained in the y-z plane and the trajectory of the edge 142 shown on the right of FIG. 4 is contained in the x-y plane. As both of the blade springs 140 are connected to the diaphragm 103, when the diaphragm 103 moves the edges 142 of each spring remain at the same height as each other. Thus, each point on one trajectory curve has a corresponding point on the other trajectory curve, showing that there is no relative movement in the y-axis between the two spring elements 140. It is possible to define a middle point between the two trajectories, which will also define a middle plane. In the case of 90-degree placement of the two blade springs 140, the middle plane lies at 45-degrees angle from each trajectory plane.
(34) FIG. 5 shows the graph of FIG. 4 from above, i.e. the x-z plane of FIG. 4. The middle plane referred to above is indicated with a dotted line in FIG. 5.
(35) In FIG. 5, the horizontal axis shows the trajectory of the edge 142 of the blade spring 140 shown on the right of FIG. 4 and the vertical axis shows the trajectory of the edge 142 of the blade spring 140 shown on the left of FIG. 4. As shown by FIG. 5, the distance between the edges 142 varies between a minimum length when the diaphragm 103 has moved by its maximum extent in the coil in direction and a maximum length when the diaphragm 103 has moved by its maximum extent in the coil out direction.
(36) When the conventional loudspeaker design of FIG. 1 is examined in view of these considerations, one may notice components which are made to expand and contract. Examples of such components include the spider 4b and edge suspension 4a. These elements are formed in such a way that their geometric stiffness will be dominant over their material stiffness. This is achieved by making them from a piece of material that is longer than the distance that they have to travel.
(37) FIG. 6 illustrates a first glue surface 143a at which a blade spring 140 is attached to the chassis 105; and a second glue surface 143b at which the blade spring 140 is attached to the diaphragm 103, when the diaphragm 103 is moved relative to the chassis 105 by the drive unit in coil in and coil out directions. As illustrated by FIG. 6, it can be seen that the distance between the first and second glue surfaces 143a, 143b always increases (elongates) when the voice coil 102a/diaphragm 103 travels away from its rest position, regardless of whether the voice coil 102a/diaphragm 103 is moved in the coil in or the coil out direction.
(38) A suspension element (e.g. a spider or edge suspension) usually has two contact surfaces. A first contact surface is used to attach (e.g. using glue) the suspension element to a rigid surface, like the chassis 105, with the second contact surface being used to attach the suspension element to a moving surface, like the diaphragm 103 or the voice coil former 102b. In any construction of a loudspeaker, the distance between these surfaces is normally at its shortest value when the voice coil 102a/diaphragm 103 is at its rest position. When the voice coil assembly and the other acoustic components of a loudspeaker start to travel in one direction, the suspension element(s) start to stretch and generate a reaction force to urge the voice coil 102a/diaphragm 103 back to its rest position. For a conventional suspension element such as the edge suspension 4a or spider 4b of FIG. 1, the reaction force, generated by stretching the suspension element, is normally mostly obtained from the geometrical stiffness of the element. This can be explained by understanding that there is a distinction between unbending a suspension element that has been bent (where stiffness is provided geometrically, by the bending of the element), and stretching material the suspension element is made of (where stiffness is provided by the material the suspension element is made of). When the geometrical stiffness provided by bending of the element is dominant over the stretching of the material, the stiffness curve of the suspension element is under the control of the geometry of the suspension element rather than the material properties of the material.
(39) As discussed in the background section (above), the use of blade springs in an edge suspension can introduce problems due a lack of sealing at corners of the edge suspension. However, providing sealing at the corners of an edge suspension that incorporates blade springs is difficult, for reasons that shall now be discussed.
(40) In detail, when the gap between the two blade springs 140 of FIG. 3(a) and FIG. 3(b) is closed using a corner portion which provides a simple continuation of the edges 142 of the blade springs 140 while they are at their rest positions (see e.g. FIG. 9), it is evident that the diaphragm 103 will not be able to move away from its rest position because the material from which the corner portion is made will need to be stretched before the blade springs 140 can deform to allow the diaphragm 103 to be moved from its rest position. In order to make the displacement of the diaphragm 103 possible, the present inventors believe that a corner portion which can expand and contract should be used to join the blade springs 140.
(41) In view of these considerations, the present inventors believe that corner portions which join the blade springs 140 would ideally fulfill the following requirements: 1. The effect of the corner portion on the stiffness of the blade springs 140 should be small (e.g. as small as possible); and 2. The corner portion should be able to seal the front side of the diaphragm 103 from the back side of the diaphragm 103.
(42) FIG. 7 shows an example corner portion 150 for joining two blade springs 140 that has been devised by the present inventors.
(43) The corner portion 150 has a first surface 151a and a second surface 151b (obscured from view in FIG. 7) which meet along an edge 152. The corner portion 150 also has at least one (in this example three) geometrical interruptions.
(44) Each geometrical interruption includes: 1. A top surface interruption 154a: this is a first corrugation which varies in height along a first path P.sub.c which extends circumferentially around the edge suspension 110. In this example, the first corrugation is a U shaped valley that is concave with respect to a front side of the edge suspension 104 and has its widest opening adjacent to the edge 152 of the corner portion 150. Note that the edge 152 is a non-continuous edge including a plurality of edge segments separated by the top surface interruptions 154a; and 2. A bottom surface interruption 154b: this is a second corrugation formed within the top surface interruption which varies in height along a second path P.sub.r which extends across the first path P.sub.c (note that each second corrugation is defined with reference to a separate, respective second path P.sub.r, though only one such path is shown in FIG. 7). In this example, the second path P.sub.r extends radially out from the edge suspension 104 within a plane in which the first path P.sub.c lies. In this example, the second corrugation is an inverted U shaped hill that is convex with respect to the front side of the edge suspension 104 and has its widest opening at the bottom of a space formed between the first surface 151a and a second surface 151b of the corner portion 150.
(45) The considerations that led to the proposed geometry of the corner portion 150 shown in FIG. 7 can be understood by the following discussion.
(46) A gap 130 between two adjacent blade springs 140 as shown in FIG. 8 could in theory be closed by continuing/extending the blade springs 140 around a curved path to provide a corner portion 150x, as shown in FIG. 9. However, this introduces further problems; because this corner portion 150x is not flexible, the material will be stretched when the diaphragm 103 is moved in either the coil in or coil out directions, and so the stiffness performance of the blade springs 140 will be adversely affected.
(47) To solve this issue, the present inventors introduced the top surface interruptions 154a to provide a corner portion 150y, as shown in FIG. 10. The top surface interruptions 154a have the ability to expand and contract when the voice coil 102a/diaphragm 103 move in the coil in or coil out directions. When the distance between the edges 142 of the blade springs 140 gets smaller (for example when the diaphragm 103 is moved in the coil in direction), the side walls of each top surface interruption 154a approach each other and geometrically absorb the deformation, without the need to stretch the material from which the corner portion 150y is formed. When the distance between the edges 142 of the blade springs 140 gets larger (for example when the diaphragm 103 is moved in the coil out direction), the side walls of each top surface interruption 154a separate from each other and enable the blade springs 140 to move freely. The top surface interruptions can therefore be seen as permitting relative movement between the edges 142 of the blade springs 140.
(48) As can be seen from FIG. 10, the base of the top surface interruptions 154a introduce a potential problem. It was mentioned previously that the blade springs 140 have only two sides of a triangle when viewed in cross-section. This is because having a third (lower) side of a triangle when viewed in cross-section would limit the movement of the diaphragm along the predetermined axis 108 of the loudspeaker. It has already been discussed with reference to FIG. 6 that the distance between first and second glue surfaces 143a, 143b on a blade spring 140 gets larger as the diaphragm 103 moves away from its rest position in either the coil in or coil out directions. The bases of the top surface interruptions 154a in the corner portion 150y as shown in FIG. 10 would therefore severely restrict movement of the diaphragm 103 in the coil in and coil out directions, since the distance between the first and second glue surfaces 143a, 143b on the blade springs 140 could only be elongated through stretching the material at the base of the top surface interruptions 154a.
(49) In view of the above considerations, the present inventors added the bottom surface interruptions 154b to provide a corner portion 150, as shown in FIG. 7. The bottom surface interruptions 154b allow the bases of the top surface interruptions 154a to expand as the coil moves in either the coil in or coil out directions, and therefore allow the distance between the first and second glue surfaces 143a, 143b on the blade springs 140 to be increased when the voice coil 102a/diaphragm 103 moves away from its rest position in either the coil in or coil out directions, without needing to stretch the material at the base of the top surface interruptions 154a. These bottom surface interruptions 154b therefore add flexibility to the bases of the top surface interruptions 154a.
(50) However, it is to be recognized that the presence of the bottom surface interruptions 154b add rigidity along the first path P.sub.c, thereby limiting the flexibility of the top surface interruptions 154a. For this reason, the bottom surface interruptions 154b preferably do not extend through the total depth of the top surface interruptions 154a. More preferably, the height of the bottom surface interruptions 154b does not exceed half the height of the top surface interruptions 154a, to allow the side walls of the top surface interruptions 154a to stay adequately flexible.
(51) The corner portion 150 of FIG. 7 can therefore be used to join blade springs 140 in a manner that permits relative movement between the edges 142 of the blade springs 140, whilst allowing the distance between first and second glue surfaces 143a, 143b on the blade springs 140 to be increased when the voice coil 102a/diaphragm 103 moves away from its rest position in either the coil in or coil out directions.
(52) The edge suspension 104 of FIG. 2, whose blade springs 140 are joined by corner portions 150 as shown in FIG. 7, can be integrally formed out of a single material, such as copper or steel, for stiffness and to provide stability. Other materials for making the edge suspension include foam, textile or paper which are flexible in many directions. Use of copper or steel may reduce internal damping of the loudspeaker where other materials may have large amounts of internal damping; the amount of damping which is desirable depends on the application of the loudspeaker.
(53) In FIG. 11, the lower curve 160 represents the stiffness, or restoring force, of the blade springs 140 relative to displacement of the diaphragm 103 (relative to its rest position) for the edge suspension 104 of FIG. 2, modified so that the corner portions 150 have been omitted. The lower curve 160 is not desirable for a loudspeaker because the maximum restoring force is achieved when the diaphragm 103 is around the rest position. The upper curve 162 represents the stiffness, or restoring force, of the blade springs 140 relative to displacement of the diaphragm 103 for the edge suspension 104 of FIG. 2 where the corner portions 150 are present and provide a seal between the front and back sides of the diaphragm.
(54) As shown by the upper curve 162 of FIG. 11, with the corner portions 150 of FIG. 7 are present in the edge suspension 104, the stiffness is lowest when the diaphragm 103 is around its rest position, as desired, and the curve is symmetric with respect to the y-axis, passing through the 0 mm displacement line. The upper curve 162 of FIG. 11 shows that as the diaphragm 103 is moved away from its rest position, in either the coil in or coil out direction, the blade springs 140 and corner portions 150 provide a restoring force to return the diaphragm to the resting position, the restoring force increasing as the displacement from the rest position increases.
(55) The edge suspension 104 of FIG. 2, whose blade springs 140 are joined by corner portions 150 as shown in FIG. 7, can be manufactured from a single piece of material instead of requiring multiple pieces of material as is the case for the suspension elements described in U.S. Pat. Nos. 4,056,697 and 6,385,327.
(56) Moreover, the edge suspension 104 of FIG. 2 can be used as the only suspension element in a loudspeaker, e.g. without the need for a spider.
(57) Moreover, the edge suspension 104 of FIG. 2 can provide sealing between the front and back sides of the diaphragm 103. Thus leakage at the corners can be eliminated, unlike in U.S. Pat. Nos. 4,056,697 and 6,385,327. Note that by using the corner portions 150 to seal the corners between the edge springs 140, the edge suspension 104 of FIG. 2 allows an engineer to reduce the air gap so as to improve efficiency of the loudspeaker, because the edge suspension 104 greatly reduces the movement of the coil in the horizontal plane without the need for a spider.
(58) The corner portions 150 could be used with an edge suspension that incorporates potentially any geometry of blade spring, e.g. such as those described in U.S. Pat. Nos. 4,056,697 and 6,385,327.
(59) The bending stiffness of the blade springs 140 of the edge suspension 104 could be improved by: 1. Introducing materials which are rigid to the straight portions of the edge suspension 104, or 2. Introducing geometrical stiffness by manipulating the geometry of the straight portions of the edge suspension 104.
(60) Examples of both techniques are given below with reference to FIGS. 12, 13 and 14. Where features correspond to those already described, corresponding reference numerals have been given and need not be described in further detail.
(61) In FIG. 12, the edge suspension 204 is made of textile material (or could be made of another material such as copper, steel, foam, or paper) and its blade springs 240 include integrally formed stiffening elements which in this example are cylindrical ridges 246 integrally formed on the first and second surfaces 241a, 241b of the blade springs 240. The cylindrical ridges 246 increase the bending stiffness of the first and second surfaces 241a, 241b therefore increasing the frequency gap between the desired first resonant frequency and unwanted second resonant frequencies. In place of cylindrical ridges 246, it is also envisaged that the geometry could be manipulated by providing corrugations in the blade springs 240.
(62) In FIG. 13, the edge suspension 304 is made of textile material (or could be made of another material such as copper, steel, foam, or paper) and its blade springs 340 include integrally formed stiffening elements which in this example are geometrical interruptions 346 having essentially the form described above in relation to the corner elements 150. Again, the geometrical interruptions 346 increase the bending stiffness of the first and second surfaces 341a, 341b therefore increasing the frequency gap between the desired first resonant frequency and unwanted second resonant frequencies.
(63) In FIG. 14, the edge suspension 404 is made of textile material (or could be made of another material such as copper, steel, foam, or paper) and its blade springs 440 include stiffening elements which in this example are planar stiffening elements 446 glued over the first and second surfaces 441a, 441b of the blade springs 440. The planar stiffening elements 446 could e.g. be made from paper or some other material such as copper, steel, or foam. The planar stiffening elements 446 help to improve the torsional stiffness of the underlying textile material. By increasing the torsional stiffness of the blade springs 440, a higher force is required to move the voice coil in the horizontal plane, thereby shifting unwanted resonant frequencies whose modes involve movement in the horizontal plane to higher frequencies. However, this torsional stiffness increase has a small influence over the vertical stiffness (i.e. stiffness in the y-axis) of the suspension element. As a result, the observed shift in the desired resonant frequency is small.
(64) The suspension element can be matched with different diaphragm geometries. For example, the diaphragm can be flat, include an inverted cone portion as shown in FIGS. 15(a) and (b), include a cone shaped portion as shown in FIG. 16 or include a dome as shown in FIG. 17, depending on the requirements of the design.
(65) When used in this specification and claims, the terms comprises and comprising, including and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the possibility of other features, steps or integers being present.
(66) The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.
(67) While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.
(68) For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The present inventors do not wish to be bound by any of these theoretical explanations.
(69) All references referred to above are hereby incorporated by reference.
