Loudspeaker voice coil bobbin

Abstract

A voice coil spool for a loudspeaker for driving a sound radiating diaphragm back and forth along an axis, the voice coil spool 2 extending axially along the axis and circumferentially around the axis, the voice coil spool being configured with perforations 6 to provide at least two rows 4a, 4b arcuate beams 10 disposed circumferentially around the voice coil spool, each arcuate beam 10 is adapted to bend in a cantilevered manner in an axial direction in response to the voice coil spool being axially driven and to allow a change in the axial length of the voice coil spool, the circumferential length of the arcuate beam being at least 25% of the circumferential length of the perforation 6.

Description

Technical Field

[0001] The present invention relates to the field of loudspeakers and in particular to a loudspeaker voice coil bobbin and a loudspeaker comprising such a voice coil bobbin. Background Art

[0002] The structure and operation of dynamic loudspeaker drive units are well known. A vibrating diaphragm is attached to a voice coil driver, and the voice coil driver is placed in a magnetic field, usually provided by one or more permanent magnets. Forces are induced by passing an alternating current through the voice coil, causing the voice coil driver to reciprocate, and thus the diaphragm to vibrate and thus radiate sound waves. The voice coil driver typically includes a voice coil bobbin or former around which an electrically conductive wire is wound; the bobbin and the wire coil form an integral item, and it vibrates as a whole. The voice coil bobbin is typically (but not always) cylindrical. In some applications where mass is critical and / or space is limited, the voice coil bobbin is made of a material such as titanium or Nomex (Nomex is a trademark of DuPont Safety & Construction, Inc., Delaware, USA). Titanium voice coil bobbins are typically formed from a flat strip of material rolled into a cylindrical shape; typically, the axial ends of the rolled strip are not joined together, which leaves a thin axial gap extending along the length of the voice coil bobbin, across which the circumferential forces cannot be balanced by symmetry. Therefore, the "hoop" stiffness acting on the circumferential force due to the axisymmetry is greatly reduced near the gap in the spool.

[0003] The use of mechanically compliant members attached to or forming part of a loudspeaker voice coil bobbin has long been considered a means of adapting the frequency response of a loudspeaker. In early arrangements, multiple voice coils and external electrical circuits were used, but more recent applications have been simpler. For example, a flexible and damped link between a loudspeaker and a voice coil driver may work in conjunction with an electrical network to form a loudspeaker system crossover network. Alternatively, the voice coil driver may have a complete mechanical crossover formed by the link.

[0004] One simple arrangement for introducing axial compliance into a voice coil driver is to provide a mechanically compliant member extending axially between the voice coil and the diaphragm, such as in GB2516936, which acts as a mechanical low pass filter to absorb energy from frequency components of the voice coil driver that oscillate above the normal operating band. This arrangement complicates the design and manufacture of the voice coil bobbin, which, in order to function, must comprise at least two different materials having different stiffnesses. Furthermore, this design is not suitable where the bobbin must be particularly stiff and made of titanium or similar material.

[0005] Another known arrangement for introducing axial compliance into a voice coil driver is to provide one or more pleats in the voice coil bobbin, the effect of which is to allow two parts of the voice coil bobbin to flex on either side of the pleats in a manner similar to a bellows. The earliest patents covering this design are US2007747 and US2007748; in which multiple voice coils and electrical filters are intended to improve the frequency response of the drive unit. In one embodiment, a driver with two coils is proposed, with a low mass coil rigidly connected to the diaphragm and a larger high mass coil connected to the low mass coil by a compliant member. The electrical filter circuit directs high frequency current to the low mass coil and low frequency current to the high mass coil. The mass of the compliant member and the coil forms a mechanical filter, allowing the force of the high mass coil to move the diaphragm and the low mass coil at low frequencies; while at high frequencies, the low mass coil is energized and moves the diaphragm without moving the high mass coil.

[0006] There are significant difficulties in manufacturing voice coil bobbins with corrugations:

[0007] 1. Thermoset and fiber-reinforced materials cannot be precisely shaped.

[0008] 2. The material formed with wrinkles in a flat sheet will deform when wound into a cylinder for a bobbin, and it is impossible to form wrinkles with the necessary accuracy in a cylindrical bobbin.

[0009] 3. The tendency of some materials to "spring back" makes it difficult to produce the exact shape required.

[0010] 4. The size of the required pleats may be too large to accommodate some applications.

[0011] 5. Changing the shape or size of the pleats to adjust the compliance of the pleats requires expensive tool changes.

[0012] There is a need for an arrangement for introducing axial compliance into a voice coil which is relatively simple, easy to manufacture and easy to "tune", particularly (but not exclusively) for use in loudspeakers where mass is critical and / or space is limited, such as in compression drivers. Furthermore, there is a need for a mechanical axial compliance arrangement which can be relatively easily adjusted to accommodate a voice coil bobbin which has been rolled into shape and has a thin axial gap extending along the length of the voice coil bobbin. One application which might benefit from the introduction of resonance would be a compression driver where the mass results in a 6 dB / octave low pass filter, typically starting at 2-3kHz. In many cases the output level in the upper part of the response is lower than desired and introducing the resonance by making the bobbin axially compliant produces a more desirable response. This can be achieved from e.g. Figure 2aThis is seen in the 'lumped element' model of an exemplary driver using a 0.025 mm thick titanium bobbin shown in . In this case the resistive impedance of the plane wave tube provides some damping.

[0013] JP 2006074410 proposes to introduce a compliance applying portion to the voice coil bobbin between the diaphragm and the voice coil winding in the form of a plurality of slit holes extending uniformly around the circumference of the voice coil bobbin. JP 2006074410 discloses two embodiments, in the first embodiment there are two rows of circumferential slit holes, and in the second embodiment there is only a single row of slit holes; in both embodiments, the arrangement of the slit holes is such that the total circumferential length of all the slit holes in any one row is 50% or more of the circumference of the voice coil bobbin. In the case of Figure 3 At paragraphs

[0020] and

[0024] of the three SPL curves in JP 2006074410, it is explained that, in the first embodiment, the high-frequency resonance peak can be greatly reduced compared to the conventional voice coil bobbin, and the cut-off characteristics of the high-frequency range are also sharply attenuated; in the second embodiment, the high-frequency resonance peak can be reduced and the cut-off characteristics of the high-frequency range are also improved compared to both the conventional voice coil bobbin and the first embodiment. We believe that the inventor of JP 2006074410 did not understand the different mechanical features and characteristics of the embodiments he described that contribute to the application of compliance. Summary of the invention

[0014] The present invention is based on the recognition that a relatively simple mechanical compliance arrangement can be provided by exploiting a relatively easy to calculate cantilever effect, and that certain cantilever arrangements can be used to form a voice coil driver having significantly improved overall performance compared to conventional systems. While JP 2006074410 discloses a first embodiment in which a cantilever is present and is approximately 20% of the circumferential length of the slit hole, it also teaches a second embodiment in which no cantilever is present and which provides better performance than the first embodiment.

[0015] Therefore, the present invention provides a voice coil bobbin for a speaker compression driver for driving a sound radiating diaphragm to reciprocate along an axis, the voice coil bobbin extending axially along the axis and extending circumferentially around the axis, the voice coil bobbin having at least two rows of axially spaced perforations, the perforations extending circumferentially or at least partially circumferentially around the axis, adjacent rows rotated relative to each other so that adjacent perforations overlap circumferentially to form arched beams circumferentially arranged around the voice coil bobbin therebetween, each arched beam being suitable for bending in a cantilever manner in an axial direction in response to the voice coil bobbin being axially driven, and allowing the axial length of the voice coil bobbin to vary, wherein the overlap between adjacent perforations in adjacent rows is such that the length of the arched beam is at least 25% of the circumferential length of the adjacent perforations.

[0016] In this arrangement, the beam forms a structural link that transfers force between the portion of the bobbin around which the voice coil is wound and the portion of the bobbin attached to the diaphragm. The beam bends in a spring-like manner and generates a restoring force when deflected, causing the arrangement to act as a spring that links the coil and diaphragm in a manner similar to a fold on the bobbin. The circumferential alignment of the beam provides increased flexibility compared to an axial beam. The bobbin and beam preferably have a constant radial thickness regardless of the axial position along the length of the bobbin; this makes the axial deformation of the bobbin both predictable and circumferentially constant.

[0017] The beams are manufactured by making a plurality of perforations in the bobbin, removing material from the bobbin so that one portion of the bobbin is joined to another portion of the bobbin joined to the diaphragm by means of a circumferential array of bending beams. The axial compliance can be varied over a wide range of values ​​by varying the length, axial depth, position, orientation or number of beams, allowing the desired axial compliance to be achieved. The length of the beams can be 30%, 35% or 40% of the circumferential length of adjacent perforations; the longer the beam, the more it can bend under a given axial load, and the greater the compliance introduced into the voice coil bobbin. The overlap must be less than 50%, otherwise the consecutive grooves will merge into each other and a clear break will be formed in the bobbin; a maximum overlap of 40% is preferred so that the circumferential dimension of the portion extending axially between adjacent perforations is sufficiently rigid. Compression molding, laser cutting, precision photolithography, high-precision micro-jet waterjet cutting, plasma cutting or micro-milling are all possible manufacturing methods, depending on the type of material to be removed. Furthermore, the beams may be varied (e.g., in position, size, shape, or orientation) to readily compensate for the circumferential effects of variations caused by axial play (where the bobbin is formed by rolling), and / or to vary the axial stiffness of the bobbin at different points around its circumference. Generally, the longer the beams, the greater the manufacturing tolerances to achieve acceptable response variations; this allows for economical manufacture of the bobbin.

[0018] The perforations may extend circumferentially or at least partially circumferentially, or at least have a portion with a circumferentially directed component about the axis, with the arched beam being formed along at least a portion of each perforation. In this case, a single row of perforations may provide the beam to give the spool the required axial compliance. There may be one, two or any number of rows of circumferential perforations extending about the axis, the perforations being oriented and / or shaped to form an arched beam suitable for bending in a cantilever manner.

[0019] There are two rows of circumferential through-holes extending around the axis, and the through-holes are axially spaced apart so that the voice coil bobbin between the through-holes in adjacent rows forms an arched beam. This arrangement with two rows of through-holes is both easy to manufacture and provides a beam that imparts axial mechanical compliance that can be relatively easily calculated using finite element method (FEM) analysis; it is also most easily adjusted to accommodate non-axisymmetry (presence of axial play) or to provide axial compliance that is itself non-axisymmetric.

[0020] Depending on the particular application, the perforations may provide ventilation; alternatively, at least some of the perforations may be filled with a damping material (which is sound absorbing and more flexible than the material from which the voice coil bobbin is made) to provide damping of air flow through the perforations, and / or at least some of the perforations may be covered with a flexible material (which is air-impermeable (and more flexible than the material from which the voice coil bobbin is made)) to prevent air flow through the perforations.

[0021] The perforations may have substantially the same shape, which ensures that all beams are similar, thereby facilitating ease of manufacture, and allowing the axial compliance effects of the beams to be calculated relatively easily. Alternatively, the perforations may have different shapes, which may help to adjust the axial compliance in the circumferential direction.

[0022] The perforations may be of substantially the same size, which ensures that all beams are similar, thereby facilitating manufacture and allowing the axial compliance effects of the beams to be calculated relatively easily. Alternatively, the perforations may be of different sizes and / or different circumferential lengths, which may help adjust axial compliance circumferentially.

[0023] The perforations may be spaced approximately the same distance circumferentially and / or axially, which ensures that all beams are similar, thereby facilitating ease of manufacture, and allowing the axial compliance effects of the beams to be relatively easily calculated. Alternatively, the perforations may be spaced different distances apart, which may help adjust axial compliance circumferentially.

[0024] The perforations may be similarly oriented, which ensures that all beams are similar, thereby facilitating ease of manufacture, and allowing the axial compliance effects of the beams to be calculated relatively easily. Alternatively, the perforations may be differently oriented, which may help to adjust the axial compliance in the circumferential direction.

[0025] The voice coil bobbin may comprise two axially concentric parts, each forming a voice coil bobbin as described above, and each comprising a plurality of perforations formed therein and extending circumferentially about the axis. Such an arrangement is suitable where low mass is not so critical. Damping may be provided by incorporating a layer of viscoelastic film sandwiched between and attached to two concentric layers of bobbin material. This creates a mechanical resistance between the two parts joined by the flexure beam, thereby damping resonance.

[0026] The concentric sections can be displaced circumferentially and / or axially so that the perforations in the two sections are not aligned. Rotating the outer section relative to the inner section provides the maximum shear force due to axial movement. Rotating the bending beams half an angle between each other provides the highest damping, less rotation provides less damping, thereby allowing some control of the mechanical resistance. Likewise, a viscoelastic material can be sandwiched between and attached to the two concentric sections.

[0027] The invention extends to voice coil drivers, compression drivers and loudspeakers incorporating a voice coil bobbin as described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will now be described by way of example and with reference to the accompanying drawings, in which:

[0029] Figure 1a is a schematic illustration of one embodiment of a voice coil bobbin according to the present invention, and Figure 1b yes Figure 1a an enlarged view of a portion of a voice coil bobbin;

[0030] Figure 2a , Figure 2b and Figure 2c is a plane wave tube simulated SPL response curve of a conventional voice coil bobbin and a voice coil bobbin according to the present invention;

[0031] Figure 3 is a schematic diagram of the voice coil bobbin of FIG. 1 in a compression driver diaphragm assembly such as in our EP2952014 / US9467782;

[0032] Figure 4a and Figure 4b is an enlarged schematic diagram of a portion of an alternative embodiment of a voice coil bobbin;

[0033] Figure 5 is an enlarged view of a portion of the voice coil bobbin of FIG. 1 showing an axial gap extending along the bobbin;

[0034] Figure 6a , Figure 6b and Figure 6c is an enlarged schematic diagram of a portion of an alternative embodiment of a voice coil bobbin where there are two concentric bobbin sections. DETAILED DESCRIPTION

[0035] Figure 1a A voice coil bobbin 2 is shown having two rows 4a, 4b of axially spaced apart perforations 6, each perforation 6 having the shape of a slot formed by two semicircles joined by straight sides extending circumferentially. In this example the bobbin is 0.025mm thick titanium, rolled into a cylinder of approximately 34mm diameter, and there are 28 perforations / slots in each row; each slot is approximately 2.2mm long, 0.2mm wide, has a radius of 0.1mm at each end, and is spaced approximately 1.1mm from the next slot in the row. The bobbin formed has a substantially constant thickness along its axial length. As Figure 1b As can be seen more clearly in FIG. 1 , between adjacent perforations 6 in each row are axially extending portions 8, and the rows 4a, 4b are rotated relative to each other so that each axially extending portion 8 is aligned with the middle of the nearest slot; this forms circumferentially extending beams 10 on either side of each axially extending portion 8, between the overlapping ends of the slots in the two rows (the beams 10 are also shown in dark shading in FIG. 1 , but for clarity these do not show beams extending to the rounded ends of the perforations, which is the actual situation, as shown in FIG. Figure 1b ). Each beam is arched because it is formed on the surface of a cylinder. In the embodiment shown, there are 56 circumferential beams in total (two beams per slot); the circumferential length of each beam is 0.7 mm, and the axial depth (i.e. the axial distance between the two rows 4a, 4b (vertical in the figure)) is 0.3 mm. In this case, the overlap (i.e. the length of each circumferentially extending arched beam) is approximately 27% of the circumferential length of each perforation.

[0036] By varying the size of the slots, their circumferential separation and / or the distance between rows, the axial compliance of this arrangement can be varied to suit specific requirements / applications and can be calculated relatively easily.

[0037] Figure 2a The SPL responses of a lumped element model ("Lumped Model") and a finite element method ("FEM Model") simulation of a 0.025 mm conventional cylindrical titanium bobbin driving a compression driver are shown. The figure shows a good match between the SPL responses of the lumped model and the FEM model except for the highest frequencies where the acoustic and structural modes limit the bandwidth. The vertical line on the graph is at 20 kHz, the upper limit of the operating frequency band. Due to computational limitations, the frequency of the FEM model is limited to 25 kHz. In this case, the resistive impedance of the plane wave tube provides some damping.

[0038] Unlike a direct radiator where a linear response is a possible result, a compression driver has a 6 dB / octave low pass filter characteristic above 2 kHz, extending up to the highest operating frequency. This 2 kHz first order low pass characteristic limits the high frequency output of the compression driver. Introducing a resonance into the upper portion of the desired operating bandwidth can provide a significant output boost, creating a region of boosted response at that resonance. For example, adding a spring with a stiffness of 2M / n between the coil and the diaphragm to the lumped model results in a resonance at 21.8 kHz.

[0039] Figure 2b shows the lumped and FEM model simulated response curves of the same compression driver driven by a voice coil bobbin incorporating 56 beams of 0.7 mm length by 0.3 mm axial depth, while Figure 2c The response curves simulated by the FEM model of a conventional unmodified bobbin without a beam (lower curve) and with a beam (upper curve) are shown. It can be seen that with a circumferential length of the beam of 0.7 mm and an axial depth of 0.3 mm, the output at 20 kHz is improved from 117 dB to 129.5 dB relative to the unmodified bobbin.

[0040] Figure 3 The voice coil bobbin 2 of Figure 1 is shown in a compression driver diaphragm assembly with a diaphragm such as disclosed in our EP2952014 / US9467782. Unlike diaphragm resonances which are weakly coupled due to irregular motion of the diaphragm, the increased axial motion at the driving point of the diaphragm is coupled as strongly as the motion due to the voice coil. This allows very high gain levels to be achieved over a relatively wide frequency bandwidth.

[0041] Figure 4a An enlarged portion of the spool 2a is shown, which is similar to Figure 1a , but the perforation shape is different; assuming the size of the perforations of adjacent beams remains constant, the shape of the perforations has a small effect on the stiffness of the beam. In this example, the 'D' shaped perforations behave in almost exactly the same way as the racetrack perforations of Figure 1, and the overlap between adjacent perforations in adjacent rows is such that the length of the arched beam is approximately 27% of the circumferential length of the adjacent perforations. The perforations can be of any shape (e.g., semi-circular, semi-oval, semi-elliptical) as long as the shape of the perforation edges forming the circumferential beam remains substantially constant / straight.

[0042] Figure 4b A portion of another voice coil bobbin 2' is shown, which is similar to Figure 1b 1 embodiment, but having three rows 4a, 4b, 4c of similarly sized and shaped perforations, and wherein the circumferential overlap between the perforations in adjacent rows is greater (and the circumferentially extending arched beams are longer), approximately 33% of the circumferential length of the perforations, which provides the voice coil bobbin with a greater amount of axial compliance than the embodiment of FIG. 1 .

[0043] Figure 5 An enlarged view of a portion of the voice coil bobbin of FIG. 1 is shown (but here the overlap between the perforations is such that the length of the arched beam is approximately 25% of the circumferential length of the adjacent perforations), now showing an axial gap 12 extending along the bobbin. By ensuring that the gap 12 is between the slots, preferably equidistant and bisects the axially extending portions 8 in one row 4a and the slots 6' in the other row 4b, a bobbin with curved beams can be designed so that there is a small variation in local axial stiffness around the circumference of the bobbin. If necessary, the length and thickness of the beams in the bobbin adjacent the gaps can be adjusted to correct for any reduction in stiffness due to variations in geometry.

[0044] Figure 1 Figure 3 , Figure 4 and Figure 5 The embodiments shown are all compression drivers, but the invention is also applicable to other types of speakers. Figure 6a , Figure 6b and Figure 6c Each shows a portion of a voice coil bobbin 26 for a conical radiator, the voice coil bobbin 26 comprising two axially concentric parts, the inner part 14 and the outer part 16 each comprising a bobbin 2 as described above with respect to Figure 1. The sound radiating horn in such a loudspeaker functions similarly to the diaphragm of a compression driver, and such loudspeakers have the same axial damping requirements, which can be addressed according to the present invention. Figure 6a In the figure, for the sake of clarity, the inner part and the outer part are shown separately. Figure 6b In the embodiment, a viscoelastic membrane 18, which is more flexible than the material of the voice coil bobbin, is sandwiched between the two parts, which acts as a damping material (preferably, the membrane 18 is also suitable for attaching the two parts together); this creates a mechanical resistance between the two parts connected by the bending beam, thereby weakening the resonance. Figure 6c Show Figure 6a and Figure 6b The two parts 14, 16 of the spool are shown in Figure 1 (damping material omitted for clarity), but the outer part is rotated circumferentially relative to the inner part. Offsetting the beams in the two parts in this way effectively increases the shear forces, and therefore the damping due to the axial motion of the beams in the two parts. As shown in the figure, a half angle rotation between the bending beams provides the highest damping, and less (or more) rotation than this, but not back to Figure 6a The aligned position in provides less damping, thus allowing some control over the mechanical resistance.

[0045] Of course, it will be appreciated that many variations may be made to the above-described embodiments without departing from the scope of the invention. For example, the invention is described primarily with reference to a cylindrical voice coil (in the form of a generally planar ring with a central hole); however, the invention is equally applicable to non-circular arrangements such as oval, elliptical or racetrack (figure 8, or triangular / square / polygonal with rounded corners) voice coils, or any shape that is symmetrical in one or two orthogonal directions lying in a general plane perpendicular to the voice coil axis and having a central hole. In addition Figure 6c In addition to or in lieu of the circumferential offset shown in Figure 6c 6, the inner and outer portions of the arrangement of FIG6 may also be axially offset. In any of the illustrated embodiments, damping material may be provided in some or all of the perforations, and / or a gas impermeable flexible material may be provided covering the inner or outer surface of any perforation. The depicted embodiments are all titanium, but may also be formed of thermoset or polyimide composite materials.

[0046] Where different variations or alternative arrangements are described above, it will be appreciated that embodiments of the invention may incorporate such variations and / or alternatives in any combination for different applications, such that features of different embodiments may be combined to form additional embodiments. For example, in a single-part bobbin, each row of circumferential perforations may include perforations that are all of the same size, shape, and orientation, or any of these features may vary within a row; additionally or alternatively, the perforations in a row may be regularly spaced, or they may be irregularly spaced, and in either case, the perforations may be of the same length or of different lengths. Any or all of these combinations may equally apply to voice coil bobbins having three or more rows of perforations. A two-part bobbin may include any variation of the foregoing single-part bobbin; for example, the inner portion may be a bobbin as shown in FIG. 1 , and the outer portion may be a bobbin as shown in FIG. 4 .

[0047] Those skilled in the art will understand that although the properties, advantages and / or applications are described above only with respect to one embodiment, these properties, advantages and applications are also applicable to other embodiments that share the same or similar features as the one described, although this is not explicitly stated herein for reasons of brevity.

Claims

1. A voice coil bobbin for a loudspeaker for driving a sound radiating diaphragm to reciprocate along an axis, the voice coil bobbin extending axially along the axis and extending circumferentially around the axis, the voice coil bobbin having at least two rows of axially spaced perforations, the perforations extending circumferentially or at least partially circumferentially around the axis, adjacent rows rotated relative to each other so that adjacent perforations overlap circumferentially to form arched beams circumferentially arranged around the voice coil bobbin therebetween, each arched beam being adapted to bend in a cantilever manner in an axial direction in response to the voice coil bobbin being axially driven, and allowing the axial length of the voice coil bobbin to vary, wherein The overlap between adjacent perforations in adjacent rows is such that the length of the arched beam is at least 25% of the circumferential length of the adjacent perforations.

2. The voice coil bobbin according to claim 1, wherein: The overlap between adjacent perforations in adjacent rows is such that the length of the arched beam is at least 30% of the circumferential length of the adjacent perforations.

3. The voice coil bobbin according to claim 1 or claim 2, wherein: The overlap between adjacent perforations in adjacent rows is such that the length of the arched beam is at least 35% of the circumferential length of the adjacent perforations.

4. The voice coil bobbin according to claim 1, 2 or claim 3, wherein: The overlap between adjacent perforations in adjacent rows is such that the length of the arched beam is at least 40% of the circumferential length of the adjacent perforations.

5. The voice coil bobbin according to any one of claims 1 to 4, wherein: At least some of the perforations are filled with a flexible sound absorbing damping material.

6. The voice coil bobbin according to any one of claims 1 to 5, wherein: At least some of the perforations are covered with a flexible, air-impermeable material.

7. The voice coil bobbin according to any one of claims 1 to 6, wherein: The perforations have substantially the same shape.

8. The voice coil bobbin according to any one of claims 1 to 7, wherein: The perforations are of substantially the same size.

9. The voice coil bobbin according to any one of claims 2 to 6, wherein: The perforations are circumferentially and / or axially spaced approximately the same distance apart.

10. A voice coil bobbin comprising two axially concentric parts, each forming a voice coil bobbin according to any one of the preceding claims and each comprising at least two rows of perforations formed therein and extending circumferentially around an axis.

11. The voice coil bobbin according to claim 7, wherein: The two axially concentric parts are displaced circumferentially and / or axially such that the perforations in the two parts are not aligned.

12. A voice coil bobbin according to claim 7 or claim 8, comprising a viscoelastic material sandwiched between and attached to the two concentric parts.

13. A voice coil actuator comprising a voice coil bobbin according to any one of the preceding claims.

14. A loudspeaker comprising a voice coil bobbin according to any one of claims 1 to 12.

Images