LOUDSPEAKER SUSPENSION
BACKGROUND
This invention relates to loudspeaker suspensions, including surrounds and spiders
Referring to FIG 1, a typical loudspeaker 14 includes a stiff cone 15 connected to a voice coil 20 at the apex of the cone The loudspeaker can include a dust cap 23 attached to the cone The voice coil 20 interacts with the magnetic circuit formed from permanent magnet 25, back plate/pole piece structure 30, and top plate 21 When the voice coil is driven by an audio signal, the cone vibrates axially to produce sound
An outer edge 40 of the cone is attached to a rigid basket 45 along an annular mounting flange 47 by suspension element 50, typically referred to as a surround The voice coil 20 and/or apex of cone 15 may be attached to another section of the rigid basket 45 by second suspension element 35, typically referred to as a spider The surround 50 is often made from a flexible material such as fabric, that allows the cone to vibrate but provides a restoring force to aide in returning the cone to an at-rest position, when the voice coil 20 is not being driven The spider 35 typically is a circular woven cloth part with concentric corrugations The suspension elements provide a restoring force (along the axial direction) and a centenng force (along the radial direction) for the moving assembly Single or multiple surrounds and/or spiders may be used m various transducer embodiments
Referring now to FIGS 2A and 3, prior art surround 50 can be seen to be a hollow semi-toroid about a center O with an inner circumferential edge 60 and an outer circumferential edge 55 As shown in FIG 3, surround 50 is depicted as having a semicircular or dome shaped cross-section taken along line A-A of FIG 2 A
FIG 4 shows a plan view of an alternative prior art surround configuration FIG 5 shows a circumferential section along line B-B of FIG 3 The example surround m FIG 4 has grooves 65 extending outward at an angle to the radial direction, over the majonty of the span from the inner to the outer circumferential edges of the surround Each groove has a V-shaped trough D at the bottom and folded corners E, F at the top
SUMMARY
In general, m one aspect, the invention features an apparatus that includes a loudspeaker suspension structure having an inner circumferential border, and an outer
circumferential border, and grooves each extending from the inner circumferential border to the outer circumferential border at an angle with respect to a normal to the inner circumferential border, a profile of a circumferential section of the suspension structure having continuous curvature
Implementations may include one or more of the following features The groove spans only a portion of the distance between the inner circumferential border and the outer circumferential border The continuous curvature is cyclical The continuous curvature includes a series of peaks and grooves and the radius of curvature of each of the peaks is greater than the radiuses of curvature of the adjacent grooves The continuous curvature includes a series of peaks and grooves and the radius of curvature of at least a portion of each of the peaks is less than (or m other examples greater than) the radiuses of curvature of the adjacent grooves The ratio of the radius of curvature of each of the peaks to the radiuses of curvature of the adjacent grooves is less than 3 (or less than 5 or less than 10) The suspension structure comprises a fractional part of a toroid The suspension structure conforms to a rolled shape The rolled shape is rolled up The rolled shape is rolled down The rolled shape comprises two or more rolls between the inner circumferential border and the outer circumferential border A radius of curvature of each of the grooves is at least about three times a thickness of a material of which the suspension structure is formed A radius of curvature of each of the grooves is at least about seven times a thickness of a material of which the suspension structure is formed Grooves are spaced regularly along a circumference of the suspension structure, each of the grooves has a depth, and a pitch of the spacing is at least about four times the depth The grooves are straight in plan view The angle of the straight grooves is in the range of 10 to 80 degrees Each of the grooves comprises a curve in plan view The angle of the curved grooves is in the range of 0 to 80 degrees The curve begins at an angle to the normal to the inner circumferential border or the outer circumferential border The curve comprises sections The sections comprise straight sections or curved sections The sections have respectively different angles with respect to the normal to the inner border The sections also comprise transition sections that smoothly the straight or curved sections The sections meet at inflection points Each of the grooves has a depth that vanes from the inner border to the outer border The vanation corresponds to the vanation m height of a pnncipal contour of the suspension structure The groove has a larger
radius of curvature than does the principal contour Each of the grooves has a generally constant depth along most of a path of the groove The groove includes two or more local minima or maxima A radial cross section of the suspension structure has a configuration of a partial toroid A radial cross section of the suspension structure has a configuration other than of a partial toroid A radial cross section of the suspension structure has two or more local minima or maxima The continuous curvature comprises a piecewise linear contour The suspension structure composes a surround The suspension structure comprises a spider
In general, m another aspect, the invention features an apparatus comprising a loudspeaker suspension structure having an inner circumferential border, and an outer circumferential border, and grooves each extending from the inner circumferential border to the outer circumferential border at an angle with respect to a normal to the inner circumferential border, the bottom of each of the grooves varying from the inner border the outer border, the variation corresponding to a variation of a principal contour of the suspension structure
In general, m another aspect, the invention features an apparatus comprising a loudspeaker suspension structure having an inner border, an outer border and a matenal thickness, grooves extending from the inner border to the outer border and separated by a groove pitch, the grooves having a groove radius of curvature, and peaks defined between the adjacent grooves and having a peak radius of curvature less than about ten times the groove radius
Implementations of the invention may include one or more of the following features The peak radius is less than about five times the groove radius The peak radius is less than about three times the groove radius The grooves are curved in plan view The grooves are straight m plan view
In general, m another aspect, the invention features a loudspeaker comprising a cone, a basket to support the cone, a surround having a partially toroidal contour, an inner circumferential border, and an outer circumferential border, the surround being formed of a matenal having a thickness, the surround flexibly connecting an outer border of the cone to the basket, peaks having an axial height and extending from the inner circumferential border to the outer circumferential border and separated by a peak pitch, the peaks defining a peak radius of curvature, and grooves extending between the adjacent peaks, the grooves defining
a groove radius of curvature, the groove radius being at least about three times the matenal thickness
Other advantages and features will become apparent from the following description and from the claims
DESCRIPTION
FIG 1 is a sectional view of a loudspeaker
FIG 2 A is a schematic plan view of a loudspeaker surround suspension element FIG 3 is a schematic plan view of an alternative loudspeaker surround suspension
element
FIG 4 is a cross-sectional view taken along line A-A in FIG 2
FIG 5 is a cross-sectional view taken along line B-B in FIG 3
FIG 6A is a plan view of a loudspeaker surround suspension element
FIG 6B is a perspective view of the surround suspension element of FIG 6 A
FIG 6C is a perspective cross-sectional view taken along line A-A of FIG 6 A
FIG 7A is a plan view of a loudspeaker surround suspension element
FIG 7B is a perspective cross-sectional view taken along line A-A of FIG 7A
FIG 8 is a partial schematic plan view of a loudspeaker surround suspension element
FIG 9 A is a circumferential profile of a loudspeaker surround suspension element
taken along line A-A of FIG 8
FIG 9B is a radial profile of a loudspeaker surround suspension element taken along
line B-B of FIG 8
FIG 9C shows a number of circumferential profiles taken along planes H-H, I-I, J-J,
andK-KofFIG 8and9B
FIGS 10A-10C are circumferential profiles of various alternative loudspeaker surround embodiments taken along line A-A of FIG 8
FIG 11A is a graphical depiction of lateral force versus displacement of various loudspeaker surround suspension elements
FIG 1 IB is a graphical depiction of axial force versus displacement of various unexercised loudspeaker surround suspension elements
FIG 11C is a graphical depiction of axial force versus displacement of various exercised loudspeaker surround suspension elements
FIG 12 is a perspective view of a loudspeaker spider suspension element
FIG 13 is a radial cross section of an alternative loudspeaker surround suspension element embodiment
FIG 14 shows a perspective view of an alternative loudspeaker surround suspension element embodiment
FIG 15 shows a cross section of a cone/surround assembly using a half roll surround in a "roll down" configuration
(In the following discussion, description of the behavior of a surround suspension element is provided, but the discussion can be generalized to include other suspension elements, such as spiders An embodiment depicting a spider is shown m Fig 12)
Referring to FIGS 6A to 6C, a semi-toroidal surround suspension element 100 is centered about an origin O and includes an inner circumferential edge 105 and an outer circumferential edge 110, separated by a radial width or span W The surround 100 can include an inner attachment flange 115 extending radially inward from the inner circumferential edge 105 and an outer attachment flange 120 extending radially outward from the outer circumferential edge 110 for connection to the cone and basket, respectively \s used herein, the surround 100 can also include a loudspeaker spider, an example of which
is shown in FIG 12 Surround 100 in FIGS 6A- 6C is shown having a single convolution (m the form of a half roll up spanning the width W), but other surround embodiments may have multiple convolutions A convolution as the term is used herein, compnses one cycle of a possibly repeating structure, where the structure is typically comprised of concatenated sections of arcs The arcs are generally circular, but can have any curvature Spider 200 in FIG 12 includes multiple (two in this case) convolutions 220,230 In other spider embodiments, more or fewer convolutions, or portions of convolutions, may be used
Although surround 100 in FIGS 6A - 6C is depicted as a partial toroidal section, other less axially symmetrical shapes for attachment to non-circular cones (e g elliptical, racetrack, or other non-circular shapes) are contemplated In places where a circumferential cross section is mentioned, it should be understood that we also mean to encompasses non-circular geometries A circumferential section A-A is shown in FIG 9A This section is taken at a constant normal distance to the inner edge of the surround suspension element For a surround with a circular geometry, this section will trace out a circle A similar section for a surround with a non circular geometry is also understood to be taken at a constant normal distance from the inner edge, but the path traced around the surround for such embodiments would no longer be circular For ease of description, we mean the term circumferential section to encompass cases of both circular and non circular surround geometries, where the section is taken at a constant normal distance from the inner suspension element edge
In places where a radial cross section is mentioned, it should be understood that we also mean to encompasses non-circular geometries A radial section B-B is shown in FIG 9B This section is taken normal to the inner edge of the surround suspension element For a surround with a circular geometry, this section will also coincide with a radial direction A similar section for a surround with a non-circular geometry is understood to be taken normal to the inner edge, but m this case the section may no longer correspond to a radius For ease of description, we understand the term radial section to mean a section taken normal to the inner edge of the suspension element, and to encompass cases of both circular and non-circular suspension element geometries
In a radial cross section, nominal shapes other than half-circular (i e a typical half roll) are also contemplated For example, some embodiments may have radial cross sections
comprised of concatenated sections of circular arcs, as would be typical of multi-roll surrounds or spiders, or have undulations along nominally circular arcs or arc sections, as shown in the example of FIG 13 Another cross section (not shown) may look like a typical half roll, but with the side walls deepended to increase the effective roll height These radial profiles can be used in toroidal shaped surrounds as depicted m FIGS 6A - 6C, or other less axially symmetrical shapes (e g elliptical, oval or racetrack, or other non-circular shapes)
The surround 100 includes a senes of grooves 125 generally extending from the inner circumferential edge 105 to the outer circumferential edge 110, at an angle to the radial direction, or more generally, at an angle to the normal of the inner edge of the surround suspension element, at the point of the groove closest to the inner circumferential edge Note that the grooves need not extend over the entire span from inner circumferential edge to outer circumferential edge The grooves (together with the non-grooved portions between the grooves) can form an undulating (e g, continuously undulating) surface on the surround along the circumferential direction Note that the grooves shown m plan view m FIG 6A, and m some subsequent figures, are depicted as straight lines having no width This is for convenience in depicting the orientation and location of the grooves The lines shown depict the location of the lowest point (the bottom) along the grooves The profile through the grooves is more fully described elsewhere
Adjacent grooves are separated by a pitch distance P (FIG 6C) This can be defined as a circumferential distance taken at a specified radial distance from the origin For convenience, the distance will be defined at the midpoint between the inner and outer edges (circumferential) of the surround Another alternative surround suspension element embodiment is shown m FIGS 7A and 7B Compared with the grooves shown m FIGS 6A-6C, the surround shown in FIGS 7A and 7B has fewer grooves 125 and larger pitch distance P Various embodiments may use arbitrary pitch distances P In some examples, the pitch distance P is uniform for all of the successive pairs of grooves around the circumference of the surround In other examples, the pitch distance could vary
Each groove 125 is oriented at an angle alpha as can be seen in FIG 6A, 7 A, and 8 Alpha is the angle between the line of the groove and a normal to the inner edge of the surround Alpha can vary over a wide range m different embodiments For embodiments where the path of the groove in plan view traverses a substantially straight line from inner
circumferential edge to outer circumferential edge, the angle alpha of the groove path is preferably between 30 and 60 degrees (or -30 to -60 degrees), although useful behavior is obtained with an angle between 10 and 80 degrees (or -10 to -80 degrees) Negative angles of alpha refer to grooves that incline m the opposite direction from the radial (or normal) to that shown in FIG 8 Grooves 125 (groove paths) can be straight in plan view as in FIG 6A or curved The radius of curvature along the length of the groove can be infinite (1 e the groove is a straight line), a finite constant, or smoothly or otherwise varying For embodiments with constant, smoothly, or otherwise varying groove curvature, alpha can vary between 0 and 90 degrees, where alpha is defined in an analogous manner to the definition given below for angle of orientation of groove sections
A groove path may comprise a plurality of sections and a plurality of transition regions The angle of orientation of each section, where angle of orientation is defined as the angle of the section at the point along the section closest to the inner circumferential edge, to a normal to the inner circumferential edge that intersects the closest point, as well as the radius of curvature of the path section, can be chosen arbitrarily and independently The radius of curvature of the path section can vary over the section Transition regions can smoothly join the ends of adjacent path sections For the case where the radius of curvature at the end of one section and the beginning of the section to which it is joined have opposite sign, the transition region will include an inflection point The number of inflection points in a groove path is arbitrary
One embodiment having two transition regions and three sections, with inflection points in each transition region, is shown in FIG 14 In this embodiment, the angle of orientation of the middle section of the groove path, where the middle section traverses the middle portion of the span W between the inner and outer circumferential edges of the surround suspension element, is smaller than the angles of the first and third sections
The shape of the surround may be better understood with reference to the profiles taken along sections of FIG 8 FIG 9 A shows a circumferential profile 140 of an exemplary surround taken along section A-A m FIG 8 Profile 140 is taken along the midpoint of the span W Peaks 145 separate adjacent grooves 125 along the profile 140 The radius of curvature of the peak is given by RP and the radius of curvature of the groove is given by RG In some examples of the embodiment of FIG 9 A, P = 0 178", RP = 0 141", RQ = 0 050", A =
0 022", and T = 0 010", where "A" is the depth of the groove m FIG 9A, and "T" is the material thickness of the suspension element, and "P" is the pitch distance between successive peaks (or grooves) It should be noted here that the radius of curvatures for the peak and groove (Rp and RG) are taken to be at the local mimma and local maxima of the section shown in FIG 9 A, and for convenience are measured thru the center line of the surround material (note that the radii of curvature could be defined elsewhere, such as along the top or bottom of the material surface as well) The value of RQ given above was obtained at the point along the groove with maximum depth, and the value of Rp given above was obtained at the point where the peak has maximum height The profile in between the groove and peak is smooth and continuous One feature of the circumferential profile of some suspension element embodiments is that the profile have continuous curvature over its entire length In such examples, the profile should be free of flat areas, such as those present in the profile shown in FIG 4 of a prior art surround Continuous curvature is desirable for a circumferential section taken along the midpoint of the span W, as illustrated by profile 140 generated from section A-A in FIG 8 It is beneficial for the continuous curvature to be present in profiles generated from other sections taken at different radial (or normal) distances from the inner circumferential edge The property of continuous curvature need not be present for profiles generated from circumferential sections taken over the entire span W, but is usefully present at least for profiles from sections taken close to the midpoint of the span W
It should be understood that one could emulate the property of continuous curvature using a piecewise linear approximation, comprised of sufficiently small length linear segments As the length of each linear segment in the approximation decreases, the behavior approaches that of a continuous curve Such an approximation is contemplated herein Some portion of the cross-section could be continuously curved while other portions could be piecewise linear
In some embodiments, Rp is greater than RG In other embodiments, the profile 140 can be generally approximated by an ordinary cycloid, where Rp is unequal to Rg In still other examples, the profile 140 is continuously curvilinear and without a constant pitch P between successive peaks
FIG 9B shows a profile 150 along line B-B in FIG 8 extending along the radial direction (or the normal to the inner circumferential edge direction) from the inner to the outer circumferential edges 105,110 of the surround Circumferential profiles of one representative groove corresponding to the section lines H-H, I-I, J-J, and K-K of FIG 8 and 9B are shown m FIG 9C Note that sections H-H, I-I, J-J, and K-K are all taken along the local perpendicular direction, with respect to the outer surface of the surround The local groove depth is defined as the distance measured along each section, from the outer surround surface, to the bottom of the groove m that section In some embodiments, the depth of the grooves ranges from a minimum proximate to the inner circumferential edge 105, along section H-H, and progressively increases with radial distance, given by sections I-I, J-J to reach a maximum midway between the inner and outer circumferential edges, given by section K-K, then progressively decreases with increasing radial distance becoming a minimum again proximate to the outer circumferential edge
Following along the path of the groove from inner to outer circumferential edges, the bottom of the groove generally follows the curvature of the principal surround surface, but typically having a larger radius of curvature Since the groove can be thought of as an inward projection of the outer surround surface, practically speaking there is no outer surround surface present directly above the bottom of the groove The curvature that the bottom of the groove generally follows is that of the principal surround surface envelope In the case of a dome shaped suspension element with grooves, the bottom of the groove would generally follow the curvature of the dome shape envelope (with larger radius of curvature) For a groove bottom that follows the surround suspension element envelope for a dome shaped surround, the radius of curvature will depend on the span W, roll height H, and the desired groove depth The radius of curvature of the groove bottom path will typically be less than 3 times (for example, two times) the radius of curvature of the surround suspension element envelope In some cases, it could be less than about 5 times (or even ten times) the radius of curvature of the surround suspension element envelope
In other embodiments, the depth of the groove may vary as a function of distance along the groove path in other ways For example, m some embodiments the groove depth may remain constant over a large percentage of the span W of the surround (l e the distance between the inner and outer circumferential edges) In other embodiments, the groove depth
may have a plurality of local maxima and minima along the groove path, forming undulations in the bottom of the groove
With reference to FIGS, 10A-10C, in some embodiments, the ratio of radius Rp to radius RG, (Rp / RG) of profile 140 is less than about 10 FIG 10A shows a profile 140 where RP / Ro is 8 8 In other embodiments, Rp / RG is less than about 5 In still other embodiments, Rp / RQ IS less than about 3 FIG 1 OB shows a profile 140 where Rp / RQ IS 2 8 FIG IOC shows a profile 140 where RP / RG IS about 1 2 Embodiments are also possible where the ratio Rp / RG is less than one
In general, both radii Rp, RG should be at least about three times greater than the material thickness T of the surround suspension element, where T is shown in FIG 9A This applies for grooves and peaks present in any circumferential section that may be taken around the surround suspension element Given a surround material thickness T of about 31 mils (0 787 mm) m one embodiment, Rp, RG are greater than about 93 mils (2 36 mm) Rp, RG should also generally be less then infinity (l e not flat), with the exception of the piecewise linear approximation mentioned earlier In general, for practical designs Rp, RG should differ from each other by no more than a factor of 20
In other examples, the pitch P between successive peaks is at least about 4 times greater than the height A of the peaks (FIG 9A) In some examples, the height A is between about 0 025 inch (0 064 cm) and 0 10 inch (0 25 cm) and the pitch P is between about 0 15 inch (0 38 cm) and about 0 6 inch (1 52 cm)
FIG 11A shows graphical relationships between lateral force applied to a surround and the lateral displacement of the surround, for vanous surround suspension elements Lateral force is any force applied to the suspension element orthogonal to the axial direction, where the axial direction is the primary direction of motion for the cone assembly Curves 160 in FIG 11A correspond to the example surround shown in FIG 7 A and 7B Curves 165 in FIG 11A correspond to the prior-art surround without grooves of FIG 2 A It can be seen that the new surround of FIGS 7A, B is substantially linear as compared with the prior art surround Onset of buckling is evidenced by a deviation from a generally linear relationship in the vanous curves, where the onset of buckling can be seen to cause abrupt discontinuities in their lateral force/displacement curves For curves 165, it can be seen that there is a

significant deviation from linear behavior indicating buckling in the surround, at only approximately 0 008 mm of lateral deflection (for zero axial excursion)
FIGS 1 IB and 11C are graphs of axial force vs axial displacement for an exemplary surround and a pnor art surround FIG 1 IB shows the behavior of unexercised surrounds, while FIG 11C shows the same surrounds after 10,000 cycles of exercise at high excursion In FIG 11B, the curves 170 and 175 correspond to the exemplary surround of FIG 7 A and 7B, and curves 180 and 185 correspond to the pnor-art surround without grooves (as shown in FIG 2 A) In FIG 11C, curves 190 and 195 correspond to the exemplary surround of FIG 7A and 7B, and curves 200 and 205 correspond to the pnor-art surround without grooves (as shown in FIG 2A)
As shown m FIGS 1 IB and 11C, the graphical relationship between the axial force applied by the voice coil and the displacement of the exemplary surround is substantially linear as compared with the pnor art surround The onset of buckling is evidenced by a deviation from a generally linear relationship in the vanous curves In particular, the downwardly-sagging shape of the curves for 180,185,200 and 205, pnor to a sharp upward ascendancy at the nght-hand side of the graphs, shows significant non-hneanty in the axial force/displacement curves of the pnor art surround compared to the exemplary surround
The radial cross section of the suspension elements desenbed herein have been shown using a "roll up" onentation That is, for suspension elements with a roll shape in radial cross section, the roll extends upward, away from the cone surface All of the embodiments herein desenbed will also function using a "roll down" onentation That is, the suspension element (surround or spider) can be flipped over 180 degrees, with provision made for changing mounting flanges to accommodate mounting to the cone and ngid basket A "roll down" half roll conventional surround suspension element is shown in FIG 15
In operation, the surround having a configuration desenbed herein reduces stress concentrations and reduces buckling
Other embodiments are within the scope of the following claims For example, although the surround and the spider are typically distinct components, separate from the cone or diaphragm, one or both may be attached to the cone usmg adhesives, heat staking, ultrasonic welding, or other joining processes to form an assembly In some implementations the surround may be formed integrally with a portion of or all of
he cone In the latter cases, the suspension structure has a virtual border even if not a discrete edge

WHAT IS CLAIMED IS:
1. Apparatus comprising:
a loudspeaker suspension structure having an inner circumferential border, and an outer circumferential border, and
grooves each extending from the inner circumferential border to the outer circumferential border at an angle with respect to a normal to the inner circumferential border,
a profile of a circumferential section of the suspension structure having continuous curvature.
2. The apparatus of claim 1 in which the groove spans only a portion of the distance between the inner circumferential border and the outer circumferential border.
3. The apparatus of claim 1 in which the continuous curvature is cyclical.
4. The apparatus of claim 1 in which the continuous curvature includes a series of peaks and grooves and the radius of curvature of each of the peaks is greater than the radiuses of curvature of the adjacent grooves.
5. The apparatus of claim 1 in which the continuous curvature includes a series of peaks and grooves and the radius of curvature of at least a portion of each of the peaks is less than the radiuses of curvature of the adjacent grooves.
6. The apparatus of claim 4 in which a ratio of the radius of curvature of each of the peaks to the radiuses of curvature of the adjacent grooves is less than 3.
7. The apparatus of claim 4 in which a ratio of the radius of curvature of each of the peaks to the radiuses of curvature of the adjacent grooves is less than 5.
8. The apparatus of claim 4 in which a ratio of the radius of curvature of each of the peaks to the radiuses of curvature of the adjacent grooves is less than 10.
9. The apparatus of claim 4 in which the radius of curvature of at least a portion of each of the peaks is greater than the radiuses of curvature of the adjacent grooves.
10. The apparatus of claim 1 in which the suspension structure comprises a fractional part of a toroid.
11. The apparatus of claim 1 in which the suspension structure conforms to a rolled shape.
12. The apparatus of claim 1 in which the rolled shape is rolled up.
13. The apparatus of claim 1 in which the rolled shape is rolled down.
14. The apparatus of claim 1 in which the rolled shape comprises two or more rolls between the inner circumferential border and the outer circumferential border.
15. The apparatus of claim 1 in which a radius of curvature of each of the grooves is at least about three times a thickness of a material of which the suspension structure is formed.
16. The apparatus of claim 1 in which a radius of curvature of each of the grooves is at least about seven times a thickness of a material of which the suspension structure is formed.
17. The apparatus of claim 1 in which grooves are spaced regularly along a circumference of the suspension structure, each of the grooves has a depth, and a pitch of the spacing is at least about four times the depth.
18. The apparatus of claim 1 in which the grooves are straight in plan view.
19. The apparatus of claim 18 in which the angle of the grooves is in the range of 10 to 80 degrees.
20. The apparatus of claim 1 in which each of the grooves comprises a curve in plan view.
21. The apparatus of claim 20 in which the angle of the grooves is in the range of 0 to 80 degrees.
22. The apparatus of claim 20 in which the curve begins at an angle to the normal to the inner circumferential border or the outer circumferential border. s
23. The apparatus of claim 20 in which the curve comprises sections.
24. The appsaratus of claim 23 in which the sections comprise straight sections.
25. The apparatus of claim 23 in which the sections comprise curved sections.
26. The apparatus of claim 23 in which the sections have respectively different angles with respect to the normal to the inner border.
27. The apparatus of claim 23 in which the sections also comprises transition sections that smoothly the straight or curved sections.
28. The apparatus of claim 23 in which the sections meet at inflection points.
29. The apparatus of claim 1 in which each of the grooves has a depth that varies from the inner border to the outer border.
30. The apparatus of claim 29 in which the variation corresponds to the variation in height of a principal contour of the suspension structure.
31. The apparatus of claim 29 in which the groove has a larger radius of curvature than does the principal contour.
32. The apparatus of claim 1 in which each of the grooves has a generally constant depth along most of a path of the groove.
33. The apparatus of claim 29 in which the groove includes two or more local minima or maxima.
34. The apparatus of claim 1 in which a radial cross section of the suspension structure has a configuration of a partial toroid.
35. The apparatus of claim 1 in which a radial cross section of the suspension structure has a configuration other than of a partial toroid.
36. The apparatus of claim 1 in which a radial cross section of the suspension structure has two or more local minima or maxima.
37. The apparatus of claim 1 in which the continuous curvature comprises a piecewise linear contour.
38. The apparatus of claim 1 in which the suspension structure comprises a surround.
39. The apparatus of claim 1 in which the suspsension structure comprises a spider.
40. An apparatus comprising
a loudspeaker suspension structure haring an inner circumferential border, and an outer circumferential border, and
grooves each extending from the inner circumferential border to the outer circumferential border at an angle with respect to a normal to the inner circumferential border,
the bottom of each of the grooves varying from the inner border the outer border, the variation corresponding to a variation of a principal contour of the suspension structure.
41. An apparatus comprising:
a loudspeaker suspension structure having an inner border, an outer border and a material thickness;
grooves extending from the inner border to the outer border and separated by a groove pitch, the grooves having a groove radius of curvature; and
peaks defined between the adjacent grooves and having a peak radius of curvature, the peak radius being less than about ten times the groove radius.
42. . The apparatus of claim 41 in which the peak radius is less than about five times the groove radius.
43. The apparatus of claim 41 in which the peak radius is less than about three times the groove radius.
44. The apparatus of claim 41 in which the grooves are curved in plan view.
45. The apparatus of claim 33 in which grooves are straight in plan view.