Double Voice Coil Loudspeaker Transducer Unit

Abstract

The present invention discloses a loudspeaker driver comprising a magnet system having at least one gap where in each gap a voice coil assembly is arranged for movement in the gap, wherein either two distinct coils are arranged on the voice coil assembly, one above the other, and the magnet system comprises two pole pieces, one above the other, creating a pair of magnetized areas between said pole pieces and a yoke, such that a magnetic flux field is created between each pole piece and the yoke. In an alternative two concentric gaps are provided, where the voice coil assembly comprises two concentrically arranged sub-voice coils, where each sub-voice coil is provided with a distinct voice coil and the magnet assembly has two concentrically arranged magnet rings arranged with a yoke in the center, such that two concentric gaps are created, and that the voice coil assembly moves substantially orthogonal to the flux fields in the gap(s) and further that at least the part of each pole piece facing the gap(s) is made from a soft magnetic composite (SMC) material.

Claims

1. A loudspeaker driver comprising: a magnet system having at least one gap where in each gap a voice coil assembly is arranged for movement in the gap, wherein either two distinct coils are arranged on the voice coil assembly, one above the other, and the magnet system comprises two pole pieces, one above the other, creating a pair of magnetized areas between said pole pieces and a yoke, such that a magnetic flux field is created between each pole piece and the yoke, or where two concentric gaps are provided, where the voice coil assembly comprises two concentrically arranged sub-voice coils, where each sub-voice coil is provided with a distinct voice coil and the magnet assembly has two concentrically arranged magnet rings arranged with a yoke in the center, such that two concentric gaps are created, and that the voice coil assembly moves substantially orthogonal to the flux fields in the gap(s) and further that at least the part of each pole piece facing the gap(s) is made from a soft magnetic composite (SMC) material.

2. The loudspeaker driver according to claim 1, wherein the two distinct coils on the or each voice coil assembly are polarized in opposite directions.

3. The loudspeaker driver according to claim 1, wherein each pole piece has an extent a orthogonal to the flux field and where each voice coil when not polarized is arranged relative to the pole piece such that the extent of the voice coil extends a distance of a into the flux field.

4. The loudspeaker river according to claim 3, wherein when the voice coils are arranged on the same voice coil, the coils are arranged with a minimum distance between the voice coils.

5. The loudspeaker driver according to claim 3, wherein when the voice coils are arranged on the same voice coil, the coils are arranged with a maximum distance between the voice coils.

6. The loudspeaker according to claim 1, wherein the yoke is provided with flux focusing means, and where optionally also the pole pieces opposite the flux focusing means on the yoke are provided with flux focusing means.

7. The loudspeaker according to claim 6 wherein the flux focusing means is a taper or decreasing thickness towards the rim in the material from which the pole piece respectively yoke is manufactured.

8. The loudspeaker according to claim 1 wherein the windings are made with an electrically conductive wire having a four-sided cross-section.

9. The loudspeaker according to claim 1 wherein the concentrically arranged sub-voice coils are connected to a plate arranged orthogonal to the direction of movement of the coils.

Description

DESCRIPTION OF THE DRAWING

[0038] The invention will now be described with reference to the accompanying drawing.

[0039] In FIG. 1 is shown a section of a loudspeaker driver;

[0040] In FIG. 2 are illustrated two variations of an embodiment where the two voice coils are arranged in a different manner in the gap;

[0041] In the FIGS. 3 and 4 the respective inductance of various combinations of materials are illustrated as a function of the frequency;

[0042] In FIGS. 5a and 5b is illustrated the dual coil system provided with special flux-focusing means;

[0043] In FIG. 6 is illustrated a cross-section through a transducer unit having two concentric gaps and voice coils.

DETAILED DESCRIPTION OF THE INVENTION

[0044] In FIG. 1 is shown a section of a loudspeaker driver according to the invention. In the figure is illustrated part of the loudspeaker driver 1 where an air gap 10 is arranged between a yoke 12 and two pole pieces 14, 16. In this manner two distinct magnetic flux fields 20, 22 are created between each pole piece 14, 16 and the yoke 12. The voice coil assembly 30 has two distinct coils 32, 34 arranged on the voice coil where the two distinct coils 32, 34 are arranged to be positioned in separate flux fields 20, 22. The voice coils 32, 34 have been mounted such that they have opposite polarity whereby the self-induction in the two coils 32, 34 substantially cancels each other out. In this manner the system's self-induction is greatly reduced.

[0045] At least a part 14, 16 of each pole piece facing the gap is made from a soft magnetic composite (SMC) material. As SMC is more expensive than regular iron, the use of SMC is used with a view to associated cost and obtained performance. The entire pole piece and yoke may be manufactured from SMC.

[0046] The SMC material provides extremely low generation of eddy currents in the gap and as such particularly when using two distinct voice coils 32, 34 in the gap, the substantial reduction of eddy currents in the voice coils facilitate that the two coils do not interfere with each other such that they may be arranged very close to each other on the voice coil assembly 30. In this manner a powerful (due to the two coils) but very compact driver unit may be constructed.

[0047] In table 1 (see above) are listed conductivity characteristics for typical materials. As is evident from the table, SMC reduces eddy currents depending on the composition of the SMC material between 100-10,000 times with respect to the other materials listed and particularly with respect to ordinary iron the reduction is approximately 10,000 times. This is a substantial reduction for these types of systems.

[0048] In FIG. 2 is illustrated two variations of an embodiment where the two voice coils are arranged in a different manner in the gap 10 as compared to the embodiment described above with reference to FIG. 1. The pole pieces have a thickness orthogonal to the flux field of a.

[0049] In the embodiment illustrated on the right hand side in FIG. 2 the voice coils 32, 34 are displaced by a such that the upper voice coil 32 extends a into the flux field created by the pole piece 14 and the yoke 12. Likewise the voice coil 34 extends a into the flux field created by the pole piece 16 and the yoke 12.

[0050] In the variation illustrated on the left hand side, the voice coils 32, 34 likewise extend a into the flux field created by the pole piece 14, 16 and the yoke 12. Due to the fact that at least part of the pole pieces 14, 16 are made from an SMC material, the voice coils can be arranged in close proximity as illustrated on the left hand side variation of the embodiment illustrated in FIG. 2 without interfering with each other. By this arrangement it is furthermore achieved that substantially a constant length of voice coil 32, 34, 32, 34 is present in the flux field as the voice coil 30 moves up and down in the gap 20.

[0051] In FIG. 2 the pole pieces 14, 16 are not illustrated as having SMC material facing the air gap, but naturally at least part of each pole piece facing the gap may likewise be made from a soft magnetic composite. This is especially important when the benefits as explained above are to be achieved, particularly when the voice coils 32, 34 are arranged in close proximity as is the case in the variation on the left hand side of the embodiment illustrated in FIG. 2.

[0052] By arranging the voice coils as illustrated with FIG. 2 an almost perfect symmetry is achieved in that the voice coils will move such that as part of one coil leaves its respective flux field, the other coil is forced further into its respective flux field.

[0053] In the FIGS. 3, 4 and 5 the respective inductance of various combinations of material are illustrated as a function of the frequency.

[0054] Basically the use of SMC materials with respect to iron-based material is that SMC reduces self-inductance.

[0055] In FIG. 3 is illustrated the performance of a SMC-based transducer unit. The curves are the result of an extensive testing in a laboratory, and consequently reflect actual measurements derived from dual coil drivers.

[0056] The inductance increases from approx. 1000 Hz and upwards(midtone speakers towards tweeters). The upper curve 40 illustrates the aggregated inductance of the two coils separately, whereas the curve 42 illustrates the inductance of each coil separatelyi.e. the coils are identical, but wound in opposite directions.

[0057] The curve illustrates a drive unit built as described above with reference to FIGS. 1 and 2, where SMC material is used on the pole pieces and the yoke. It is clear that the generated inductance cancels out to a value lower than each separate coil (i.e. 1+1 equals more than 2). The two coils therefore have a beneficial relationship, resulting in a better dampening than what could otherwise be expected, when measuring the two coils separately.

[0058] A corresponding pattern is illustrated in FIG. 4, where the driver is made from traditional iron-based material. It appears that the inductance of this system cancels out only to a degree between the sum of the coils and each separate coil.

[0059] Overall the SMC cancels out with a dual coil arrangement as discussed above to about the same level of iron based materials, and therefore reaps the benefits of iron and the superior characteristics of SMC at the same time.

[0060] By using SMC the eddy-currents are greatly reduced as compared to irona factor 100 to 10000, due to the low conductivity of SMC as compared to ironsee table 1 above. The combination of very little eddy currents and the compact construction as suggested in the present invention, assures that the two coils' self-induction substantially is compensated/cancelled, and at the same time the coils will be exposed to (able to see) equal amounts of iron, and thereby generate a symmetry in the construction to the benefit of the resulting characteristics of the system.

[0061] Iron systems shield the two coils from each other due to the relatively high presence of eddy currents and particularly at higher frequencies the eddy current loss is significant, whereas with SMC based systems, and thereby inherent very low eddy currents the coils can see each other at all frequencies, assuring improved performance over the entire frequency range.

[0062] In FIG. 5a the dual coil system is provided with special flux-focusing means 46, 47, 48, 49, whereby the magnetic flux field in the gap 20 is more focused. Due to the relatively large distance between the coils (32, 34) on the voice coil (30), and the fact that the SMC materials can see each other (which is not the case in iron systems) the focused flux fields have a large effect as compared to comparable iron systems. On the other hand it is also desirable, with respect to the B-field, to provide a relatively thick magnet (50) between the two pole pieces (14,16), in order to space the pole pieces.

[0063] In FIG. 5b is schematically illustrated a plane view of a loudspeaker driver 1 comprising a yoke 12, surrounded by pole pieces 14,16, Between the yoke 12 and the pole pieces 14, 16 is provided the air gap 20 in which the voice coil (not illustrated) reciprocates in and out of the plane of the figure. The flux focusing means 46, 47, 48, 49 are in this embodiment in the shape of ring-shaped protrusions in intimate and conductive contact with the yoke and the pole pieces respectively, such that the magnetic flux from the yoke and pole pieces can be concentrated across the air gap.

[0064] In FIG. 6 is illustrated a cross-section through a transducer having two gaps 10, 10. The gaps 10, 10 are concentrically arranged around the yoke 12. In each circular gap 10, 10 is arranged a voice coil 32, 34. As was the case as explained with reference to FIG. 1 two distinct flux fields 20, 22 are created in the gaps 10, 10. On either side of the gaps 10, 10 is arranged SMC material. In practice the pole pieces 14, 16 are rings of SMC material arranged on top of ring magnets 60. The ring magnets 60 are in contact via an iron piece 61.

[0065] The voice coils 32, 34 are arranged in the gaps 10, 10 and held by a voice coil assembly plate 62, which either directly or indirectly is in contact with the loudspeaker membrane/cone (not illustrated).