Loudspeaker voice coil bobbin

Abstract

To provide a voice coil bobbin for a loudspeaker that drives a sound-emitting diaphragm in reciprocating motion along an axis.SOLUTION: A voice coil bobbin 2 extends axially along the axis and circumferentially about the axis and is configured to comprise perforations 6 to provide at least two rows 4a, 4b of arcuate spars 10 circumferentially disposed about the voice coil bobbin. Each of the arcuate spars 10 is adapted to flex axially in a cantilever manner in response to the voice coil bobbin being axially actuated to allow for a change in the axial length of the voice coil bobbin, and has a circumferential length that is at least 25% of the circumferential length of the perforations 6.SELECTED DRAWING: Figure 1a

Description

Technical Field

[0001] The present invention relates to the field of loudspeakers, and more particularly, to a voice coil bobbin of a loudspeaker and a loudspeaker incorporating such a voice coil bobbin.

Background Art

[0002] The structure and operation of a moving coil loudspeaker drive unit are known. A vibrating diaphragm is attached to a voice coil driver, which is usually placed in a magnetic field obtained by one or more permanent magnets. By passing an alternating current through the voice coil, a force is induced, causing the voice coil driver to move back and forth, vibrating the diaphragm and radiating sound waves. The voice coil driver usually includes a voice coil bobbin or former. A conductive wire is coiled around it, and the bobbin and the wire coil form an integral article that vibrates as one. The voice coil bobbin is usually (but not always) cylindrical. In applications where mass is important and space is limited, the voice coil bobbin is made of materials such as titanium or Nomex® (Nomex is a trademark of DuPont Safety & Construction, Inc. of Delaware, USA). A titanium voice coil bobbin is usually formed from a flat material strip rolled into a cylinder. Usually, the axial ends of both sides of the rolled strip are not joined, so an axial thin gap extending along the length of the voice coil bobbin remains, and the circumferential force across this gap cannot be balanced by symmetry. As a result, the "hoop" stiffness acting on the circumferential force due to axial symmetry is significantly reduced near the gap of the bobbin.

[0003] The use of a mechanical compliance member attached to or forming part of the voice coil bobbin of a loudspeaker has long been known as a means of adapting the frequency characteristics of the loudspeaker. In early configurations, multiple voice coils and external electrical circuits were used, but recent applications have been more streamlined. For example, a flexible and damping link between the speaker and the voice coil driver can, in conjunction with an electrical network, form the crossover network of a loudspeaker system. Alternatively, the voice coil driver can have a complete mechanical crossover formed by the link.

[0004] One simple configuration for introducing axial compliance into a voice coil driver is, as in Citation 1, to provide an axially extending mechanical compliance member between the voice coil and the diaphragm. This mechanical compliance member acts as a mechanical low-pass filter that absorbs energy from the frequency components of the vibration of the voice coil driver above the normal operating band. Such a configuration complicates the design and manufacture of the voice coil bobbin. The voice coil bobbin needs to include at least two different materials with different rigidities in order to function. Furthermore, such a design is not suitable when the bobbin requires particular rigidity and is made from, for example, titanium.

[0005] Another well-known configuration for introducing axial compliance into a voice coil driver was to provide one or more corrugations in the voice coil bobbin. The effect is to allow two portions of the voice coil bobbin on either side of the corrugation to flex in a bellows-like manner. The earliest patents covering such designs are Patent Documents 2 and 3, where multiple voice coils and electrical filters are intended to improve the frequency characteristics of the drive unit. In one embodiment, a driver is proposed that includes two coils, a low-mass coil rigidly coupled to the diaphragm and a larger high-mass coil coupled to the low-mass coil via a compliance member. The electrical filter circuit directs high-frequency current to the low-mass coil and low-frequency current to the high-mass coil. By forming a mechanical filter with the compliance member and the mass of the coils, at low frequencies the force of the high-mass coil displaces the diaphragm and the low-mass coil, while at high frequencies the low-mass coil is energized and displaces the diaphragm without displacing the high-mass coil.

[0006] There are significant difficulties in manufacturing a voice coil bobbin having corrugations, as follows. 1. Thermosetting materials and fiber-reinforced materials cannot be precisely formed. 2. Materials with corrugations formed in a flat sheet deform when wound around a cylinder for the bobbin, so it is impossible to form corrugations with the required accuracy in a cylindrical bobbin. 3. Due to the tendency of some materials to "spring back", it is difficult to manufacture the required precise shape. 4. The required size of the corrugations is too large to fit in some applications. 5. To adjust the compliance of the corrugations, expensive tool changes are required to modify the shape or size of the corrugations.

[0007] Particularly (but not limited to) for loudspeakers where mass is important and / or space is limited, such as compression drivers, a configuration is needed that introduces axial compliance into a relatively simple, easily manufacturable, and "tunable" voice coil. Further, considering a voice coil bobbin formed by a roll and having a narrow axial gap extending along the length of the voice coil bobbin, a mechanically axial compliance configuration that is relatively easily tunable is needed. One application that can benefit from introducing resonance is a compression driver where the mass typically provides a 6 dB / octave low-pass filter from 2 to 3 kHz. In many cases, the output level at the upper part of the response is lower than desired, and introducing resonance by making the bobbin axially compliant can result in a desirable response. This can be seen from the "lumped element" model of an exemplary driver using a titanium bobbin with a thickness of 0.025 mm, as shown in FIG. 2a. In this case, the resistive impedance of the plane wave tube provides some attenuation.

[0008] Patent Document 4 proposes introducing a compliance-providing portion in the form of a plurality of slit holes that extend evenly around the outer circumference of a voice coil bobbin between a diaphragm and a voice coil winding. Patent Document 4 discloses a first embodiment in which two rows of slit holes are provided in the circumferential direction and a second embodiment in which only one row of slit holes is provided. In any of the embodiments, the configuration of the slit holes is such that the total circumferential length of the slit holes in any one row is 50% or more of the circumferential length of the voice coil bobbin. Patent Document 4 states in paragraphs 0020 and 0024 referring to the three SPL curves in FIG. 3 that, compared with a conventional voice coil bobbin, in the first embodiment, the high-frequency resonance peak can be significantly reduced and the cutoff characteristics in the high-frequency range also rapidly attenuate, and in the second embodiment, compared with both the conventional voice coil bobbin and the first embodiment, the high-frequency resonance peak can be reduced and the cutoff characteristics in the high-frequency range are also improved. The inventor of Patent Document 4 is considered not to have understood the different mechanical features and characteristics of the embodiments described as contributing to compliance provision.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

[0010] The present invention is premised on the recognition that a relatively simple mechanical compliance configuration can be obtained by utilizing the effect of a cantilever that is relatively easily calculated, and that a voice coil driver with significantly improved overall performance compared to a conventional system can be formed by utilizing a cantilever of a predetermined configuration. Patent Document 4 discloses a first embodiment in which a cantilever exists and the cantilever is about 20% of the circumferential length of the slit hole, but also teaches that a second embodiment without a cantilever provides better performance than the first embodiment.

[0011] Accordingly, the present invention provides a voice coil bobbin for a loudspeaker compression driver that drives a diaphragm that radiates sound so as to reciprocate along an axis. The voice coil bobbin extends axially along the axis and circumferentially around the axis. The voice coil bobbin has at least two axially spaced rows of perforations that extend circumferentially around the axis or at least partially circumferentially. By rotating adjacent rows relative to each other, adjacent perforations overlap circumferentially, and an arcuate spar arranged circumferentially around the voice coil bobbin is formed between the adjacent perforations. Each arcuate spar is adapted to flex axially in a cantilever manner in response to the voice coil bobbin being driven axially to allow a change in the axial length of the voice coil bobbin, and the overlap between adjacent perforations of adjacent rows is such that the length of the arcuate spar is at least 25% of the circumferential length of the adjacent perforations.

[0012] In such a configuration, the spar forms a structural link that transmits 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 spar flexes like a spring, and the resulting restoring force during deflection causes the configuration to behave as a spring that links the coil and the diaphragm, similar to the pleats in the bobbin. By aligning the spurs in the circumferential direction, the flexibility is increased compared to the axial spurs. The bobbin and the spurs 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 predictable and circumferentially uniform.

[0013] Spurs are manufactured by making a plurality of perforations in a bobbin. This is by removing material from the bobbin. A portion of the bobbin is linked to another portion of the bobbin joined to a diaphragm via a circumferential array of flexible spurs. By varying the length, axial depth, position, orientation, or number of the spurs, the axial compliance can vary over a wide range, allowing the desired axial compliance to be achieved. The length of the spur may be 30%, 35%, or 40% of the circumferential length of the adjacent perforation. The longer the spur, the more it can bend under a given axial load and the more compliance can be introduced into the voice coil bobbin. The overlap should be less than 50%. Otherwise, continuous slots will merge with each other and create a clean cut in the bobbin. A maximum overlap of 40% is preferred so that the circumferential dimension of the axial extending portion between adjacent perforations is sufficiently rigid. Depending on the type of material to be removed, the manufacturing method can be press tool forming, laser cutting, precision photoetching, high-precision microjet water cutting, plasma cutting, or micro milling. Further, these spurs can be varied (e.g., in position, size, shape, or orientation) to easily compensate for various circumferential effects arising from the axial gap in which the bobbin is formed by a roll and / or to vary the axial rigidity at different points around the bobbin. Generally, the longer the spur, the larger the manufacturing tolerances to achieve an acceptable variation in responsiveness. This allows for the economical manufacture of the bobbin.

[0014] The perforations may extend circumferentially, or at least partially circumferentially, or have portions with at least a circumferential orientation component about the axis, and arcuate spurs are formed along at least a portion of each perforation. In this case, a row of perforations provides spurs that impart the necessary axial compliance to the bobbin. The circumferential row of perforations extending about the axis may be one, two, or any number, and the perforations are oriented and / or shaped to form arcuate spurs adapted to bend in a cantilever manner.

[0015] There are two circumferential rows of perforations that extend around the axis and are axially spaced such that arcuate spurs are formed between the perforations in adjacent rows of the voice coil bobbin. A configuration with such two rows of perforations is easy to manufacture and provides spurs that give a given axial mechanical compliance that can be calculated relatively easily using finite element method (FEM) analysis. Also, this arrangement is most easily tuned to accommodate non-axisymmetry (the presence of an axial gap) or to give an axially compliant that is itself non-axisymmetric.

[0016] The plurality of perforations may provide venting, or alternatively, at least some of the plurality of perforations may be filled with either a sound-absorbing damping material that attenuates the air flow through the perforations or a more flexible material than the material from which the voice coil bobbin is made, and / or, depending on the particular application, at least some of the plurality of perforations may be covered with a flexible material that does not allow air to pass through (and is more flexible than the material from which the voice coil bobbin is made) to prevent air flow through the perforations.

[0017] The plurality of perforations may be substantially the same shape, which ensures that all spurs are similar, makes manufacturing easier, and makes the calculation of the axial compliance effect of the spurs relatively easy. Alternatively, the plurality of perforations may be of different shapes, which can help tune the axial compliance circumferentially.

[0018] The plurality of perforations may be substantially the same size, which ensures that all spurs are similar, makes manufacturing easier, and makes the calculation of the axial compliance effect of the spurs relatively easy. Alternatively, the plurality of perforations may be of different sizes and / or different circumferential lengths, which can help tune the axial compliance circumferentially.

[0019] The plurality of perforations may be circumferentially spaced apart by substantially the same distance in the circumferential direction and / or axially spaced apart, whereby all the spurs are ensured to be similar, facilitating manufacturing and making the calculation of the axial compliance effect of the spurs relatively easy. Alternatively, the plurality of perforations may be spaced apart by different distances, which may help tune the axial compliance in the circumferential direction.

[0020] The plurality of perforations may be in a similar orientation, whereby all the spurs are ensured to be similar, facilitating manufacturing and making the calculation of the axial compliance effect of the spurs relatively easy. Alternatively, the plurality of perforations may be in different orientations, which may help adjust the axial compliance in the circumferential direction.

[0021] The voice coil bobbin may include two coaxial parts, each part forming the voice coil bobbin as described above and each including a plurality of perforations formed therein and extending circumferentially about the axis. Such a configuration is suitable when low mass is not as critical. Damping is obtained by incorporating a layer of viscoelastic film sandwiched and affixed between two concentric layers of the bobbin material. As a result, the mechanical resistance between the two parts linked by the flexing spurs damps the resonance.

[0022] The concentric parts may be displaced circumferentially and / or axially such that the perforations of the two parts are not aligned. Rotating the outer part relative to the inner part results in the greatest shear due to axial movement. The highest damping is obtained by rotating by half the angle between the flexing spurs, less rotation than this results in lower damping, and the mechanical resistance can be controlled to some extent. Also in this case, the viscoelastic material may be sandwiched and affixed between the two concentric parts.

[0023] The present invention also extends to voice coil drivers, compression drivers, and loudspeakers incorporating the voice coil bobbin described herein.

Brief Description of the Drawings

[0024] The present invention will now be described by way of example with reference to the following accompanying drawings.

[0025]

Fig. 1a

Fig. 1b

Fig. 2a

Fig. 2b

Fig. 2c

Fig. 3

Fig. 4a - 4b

Fig. 5

Fig. 6a - 6c

Embodiments for Carrying Out the Invention

[0026] Figure 1a shows a voice coil bobbin 2 having perforations 6 in two axially spaced-apart rows 4a, 4b. Each perforation 6 has the shape of a slot formed by two semi-circles joined by a straight edge, and the straight edge extends circumferentially. In this example, the bobbin is made of titanium with a thickness of 0.025 mm, rolled into a cylindrical shape with an approximate diameter of 34 mm, and there are 28 perforations / slots in each row. Each slot is approximately 2.2 mm in length, 0.2 mm in width, has a radius of 0.1 mm at each end, and is approximately 1.1 mm spaced from the next slot in the row. The formed bobbin has a substantially constant thickness along its axial length. As clearly shown in Figure 1b, between adjacent perforations 6 of each row, there is an axially extending portion 8, and the rows 4a, 4b rotate relative to each other such that each axially extending portion 8 aligns with the center of the nearest slot. Thereby, circumferentially extending spurs 10 are formed on both sides of each axially extending portion 8 between the ends of the slots in the two overlapping rows (multiple spurs 10 are shown in Figure 1 in dark hatching. However, these do not show the spurs that extend to the rounded ends of the actual perforations as shown in Figure 1b for clarity). Since each spur is formed on the surface of the cylinder, it is arc-shaped. In the illustrated embodiment, there are a total of 56 circumferential spurs (2 spurs per slot). Each spur has a circumferential length of 0.7 mm and an axial depth (i.e., the axial distance between the two rows 4a, 4b (the vertical direction in the drawing)) of 0.3 mm. The overlap (i.e., the length of each arc-shaped spur extending circumferentially) is, in this case, approximately 27% of the circumferential length of each perforation.

[0027] By varying the size of the plurality of slots, their circumferential spacing, and / or the distance between the rows, it is possible to vary the axial compliance of this configuration to suit specific requirements / applications. This axial compliance can be calculated relatively easily.

[0028] Figure 2a shows the SPL responses simulated by the lumped element model ("lumped model") and the finite element method ("FEM model") of a conventional cylindrical titanium bobbin with a diameter of 0.025 mm that drives a compression driver. This figure shows that the SPL responses of the lumped model and the FEM model are in good agreement except at very high frequencies where the acoustic and structural modes limit the bandwidth. The vertical line in the graph is 20 kHz, which is the upper limit of the operating band. The FEM model is limited to a frequency of 25 kHz due to computational constraints. In this case, the resistive impedance of the plane wave tube provides some attenuation.

[0029] Unlike a direct radiator that can achieve a linear response, a compression driver has a 6 dB / octave low-pass filter characteristic that extends up to the maximum operating frequency and exceeds 2 kHz. This 2 kHz first-order low-pass characteristic limits the high-frequency output of the compression driver. Introducing resonance towards the upper part of the desired operating bandwidth significantly boosts the output. As a result, the region of the response below the resonance is boosted. For example, adding a spring with a stiffness of 2 M / n to the lumped model between the coil and the diaphragm results in resonance at 21.8 kHz.

[0030] Figure 2b shows the response curves of simulations by the lumped model and the FEM model of the same compression driver driven by a voice coil bobbin incorporating 56 spurs with a length of 0.7 mm and an axial depth of 0.3 mm, while Figure 2c shows the response curves of simulations by the FEM model of a conventional unmodified bobbin without spurs (lower curve) and with spurs (upper curve). It can be seen that the output at 20 kHz is boosted from 117 dB to 129.5 dB for the unmodified bobbin due to the spurs with a circumferential length of 0.7 mm and an axial depth of 0.3 mm.

[0031] Figure 3 shows a schematic view of the voice coil bobbin of FIG. 1 in a compression driver - diaphragm assembly with a diaphragm as disclosed in our European Patent No. 2952014 specification / US Patent No. 9467782 specification. Different from diaphragm resonance with weak radiative coupling due to irregular movement of the diaphragm, increased axial movement at the drive point of the diaphragm couples as strongly as the movement caused by the voice coil. Thereby, a very high level of gain can be achieved over a relatively wide bandwidth.

[0032] FIG. 4a is an enlarged portion of a bobbin 2a similar to that of FIG. 1a but having perforations of different shapes. If the size of the perforations adjacent to the spurs is maintained constant, the shape of the perforations has little effect on the rigidity of the spurs. In this example, the "D" - shaped perforations exhibit approximately the same behavior as the race - track perforations of FIG. 1, with adjacent perforations in adjacent rows overlapping such that the length of the arcuate spur is approximately about 27% of the circumferential length of the adjacent perforations. If the shape of the perforation edges forming the circumferential spurs remains substantially constant / straight, the perforations can be of any shape (e.g., semi - circular, semi - oval, semi - elliptical).

[0033] FIG. 4b shows a portion of another voice coil bobbin 2' similar to that of FIG. 1b but having three rows 4a, 4b, 4c of perforations of similar size and shape, with a large degree of circumferential overlap between the perforations in adjacent rows (and a long arcuate spur extending circumferentially of the perforations), being approximately 33% of the circumferential length of the perforations. This results in a greater axial compliance of the voice coil bobbin than in the embodiment of FIG. 1.

[0034] FIG. 5 is an enlarged view of a part of the voice coil bobbin of FIG. 1 (wherein, here, the overlap between the perforations is such that the length of the arcuate spur is approximately 25% of the circumferential length of the adjacent perforation), and this time shows an axial gap 12 extending along the bobbin. By ensuring that the gap 12 exists between the slots and is preferably equidistant, and by bisecting the axial extension 8 of one row 4a of the plurality of rows and the slot 6' of the other row 4b of the plurality of rows, a bobbin with a flexing spur can be designed such that there is little variation in the local axial rigidity around the circumference of the bobbin. If necessary, the length and thickness of the spur adjacent to the gap of the bobbin may be adjusted to correct for the reduction in rigidity due to the change in the geometric shape.

[0035] The embodiments of FIGS. 1, 3, 4, and 5 are all compression drivers, but the present invention is also applicable to other types of loudspeakers. FIGS. 6a, 6b, and 6c each show a part of the voice coil bobbin 26 for a cone radiator. This voice coil bobbin 26 includes two axially concentric components, and each of the inner component 14 and the outer component 16 includes the bobbin 2 described above in connection with FIG. 1. The horn that radiates sound in such a loudspeaker has the same function as the diaphragm of a compression driver. Since such a loudspeaker has the same requirements for axial attenuation, it can be addressed according to the present invention. In FIG. 6a, the inner and outer components are shown separately for clarity, but in FIG. 6b, there is a highly viscoelastic film 18 of flexible material of the voice coil bobbin sandwiched between the two components that act as damping materials (the film 18 is also preferably adapted to bond the two components together). As a result, mechanical resistance occurs between the two components linked by the flexing spurs that damp resonance. FIG. 6c shows the two components 14, 16 of the bobbin of FIGS. 6a and 6b (the damping material is omitted for clarity), but the outer component is rotated circumferentially relative to the inner component. Thus, offsetting the spurs in the two components is effective in increasing the shear force, and thus the attenuation, resulting from the axial movement of the spurs in the two components. As shown in the drawings, rotating by half the angle between the flexing spurs results in the highest attenuation, and less (or more) rotation than this, without returning to the aligned position in FIG. 6a, results in lower attenuation, and thus the mechanical resistance can be controlled to some extent.

[0036] Of course, it is understood that many variations can be made to the above-described embodiments without departing from the scope of the present invention. For example, although the present invention has been mainly described with reference to a cylindrical voice coil (in the form of a substantially planar ring having a central hole), the present invention is equally applicable to non-circular configurations such as voice coils in the shape of an oval, ellipse, or racetrack (figure-eight, or rounded-corner triangle / square / polygon), or to any shape having a central hole that is symmetric in one or two orthogonal directions existing in a general plane perpendicular to the voice coil axis. The inner and outer components of the configuration in FIG. 6 may be offset axially, either in the same manner as the circumferential offset shown in FIG. 6c, or instead. In any of the illustrated embodiments, damping material may be provided in some or all of the plurality of perforations, and / or a flexible material that does not allow air passage may be provided to cover the inner or outer surface of any of the plurality of perforations. Although all of the described embodiments are of titanium, they may also be formed from a thermosetting or polyimide composite material.

[0037] Where different variant or alternative configurations are described, it should be understood that embodiments of the present invention can incorporate such variations and / or alternatives in any combination for different applications, and that the features of different embodiments can be combined to form further embodiments. For example, in a single-component bobbin, the perforations in each circumferential row may all include perforations of the same size, shape, and orientation, or any of these features may be varied within a row. Additionally or alternatively, the perforations in a row may be regularly spaced or irregularly spaced. In either case, the plurality of perforations may be of the same length or of different lengths. Any or all of these combinations can be similarly applied to a voice coil bobbin having three or more rows of perforations. The two-component bobbin may include any variant of the aforementioned single-component bobbin. For example, the inner component may be the bobbin shown in FIG. 1, and the outer component may be the bobbin shown in FIG. 4.

[0038] One skilled in the art will understand that, in this specification, when attributes, advantages, and / or applications are described in relation to only one embodiment, these attributes, advantages, and applications will equally apply to other embodiments that share the same or similar features as the described one embodiment, even if they are not explicitly stated in this specification for reasons of brevity.

Claims

1. 1. A voice coil bobbin for a loudspeaker that drives a sound-emitting diaphragm in a reciprocating motion along an axis, the voice coil bobbin extending axially along the axis and circumferentially about the axis, the voice coil bobbin having at least two axially spaced rows of perforations that extend circumferentially or at least partially circumferentially about the axis, adjacent rows being rotated relative to one another such that adjacent perforations circumferentially overlap and arcuate spurs circumferentially disposed about the voice coil bobbin are formed between the adjacent perforations, each arcuate spur adapted to flex axially in a cantilever manner in response to the voice coil bobbin being axially actuated to permit a change in an axial length of the voice coil bobbin, and an overlap between adjacent perforations in adjacent rows is such that a length of the arcuate spur is at least 25% of a circumferential length of the adjacent perforations.

2. 2. The voice coil bobbin of claim 1, wherein adjacent perforations in adjacent rows overlap such that a length of the arcuate spar is at least 30% of a circumferential length of the adjacent perforations.

3. 3. The voice coil bobbin of claim 1 or 2, wherein adjacent perforations in adjacent rows overlap such that a length of the arcuate spar is at least 35% of a circumferential length of the adjacent perforations.

4. 4. The voice coil bobbin of claim 1, 2 or 3, wherein adjacent perforations in adjacent rows overlap such that a length of the arcuate spar is at least 40% of a circumferential length of the adjacent perforations.

5. 5. A voice coil bobbin as claimed in claim 1, wherein at least some of the perforations are filled with a flexible, sound absorbing, damping material.

6. 6. The voice coil bobbin of claim 1, wherein at least some of the perforations are covered with an airtight flexible material.

7. 7. The voice coil bobbin of claim 1, wherein the perforations are substantially the same shape.

8. 8. The voice coil bobbin of claim 1, wherein the perforations are substantially the same size.

9. 7. The voice coil bobbin of claim 2, wherein the perforations are circumferentially and / or axially spaced at substantially the same distance.

10. 10. A voice coil bobbin comprising two axially concentric parts, each part forming a voice coil bobbin according to any one of claims 1 to 9, each including at least two rows of perforations formed therein and extending circumferentially about said axis.

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

12. 9. A voice coil bobbin as claimed in claim 7 or 8, comprising a viscoelastic material sandwiched between and affixed to said two concentric parts.

13. A voice coil driver comprising a voice coil bobbin according to any one of claims 1 to 12.

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

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