WO2001080600A1

WO2001080600A1 - An electro-acoustic transducer, a loudspeaker system comprising at least one such transducer, a method of manufacturing an electro-acoustic transducer and a method for producing an electro-acoustic transducer

Info

Publication number: WO2001080600A1
Application number: PCT/SE2001/000845
Authority: WO
Inventors: Erik Liljehag; Martin Löfgren; Gunnar Löfgren
Original assignee: Erik Liljehag; Loefgren Martin; Loefgren Gunnar
Priority date: 2000-04-18
Filing date: 2001-04-18
Publication date: 2001-10-25
Also published as: SE0001461L; SE0001461D0; AU2001248985A1

Abstract

A electro-acoustic transducer of ribbon type comprise a frame unit (10), at least two elongated magnet units (14), and at least one electrically conducting elongated membrane (13), wherein the frame unit (10) comprises at least two longitudinal supporting profiles (11a, 11b) of a non-ferro-magnetic material. The longitudinal supporting profiles (11a, 11b) are arranged in parallel with each other and spaced apart from each other, whereby two adjacent longitudinal supporting profiles (11a, 11b) form an elongated gap (12). The electrically conducting elongated membrane(s) (13) is/are provided in said gap(s) (12) and it(they) is/are electrically coupled to enable the passing of a drive current in the longitudinal direction of the membrane (13). The magnet units (14) are arranged with a pole of one polarity of a first magnet unit (14) facing a pole of opposite polarity of a second magnet unit (14), and they are supported in the longitudinal supporting profiles (11a, 11b). The invention also refers to a loudspeaker system comprising at least one such transducer, a method of manufacturing an electro-acoustic transducer and a method for producing an electro acoustic transducer.

Description

AN ELECTRO-ACOUSTIC TRANSDUCER, A LOUDSPEAKER SYSTEM COMPRISING AT LEAST ONE SUCH TRANSDUCER, A METHOD OF MANUFACTURING AN ELECTRO- ACOUSTIC TRANSDUCER AND A METHOD FOR PRODUCING AN ELECTRO- ACOUSTIC TRANSDUCER

Electro-acoustic transducer

Technical field of the invention

The present invention relates to an electro-acoustic transducer, in particular of the type that comprises a source of sound formed from an electrically conducting membrane in a homogenous magnet field with high flux.

Related art

Electro -acoustic transducers of this type usually are referred to as ribbon speakers, due to the ribbon shaped membrane. A ribbon speaker comprises an elongated, electrically conducting membrane, inserted between two elongated magnet elements. Such a speaker represents a linearly extended source of sound, having the ability to emit a high sound pressure. This type of electro- acoustic transducer can be used for all purposes where a natural sound is desired, such as for use in domestic Hi-Fi systems, in recording studios and in public address (PA) systems.

In conventional ribbon speakers, the magnet units comprise one or more magnets, supported by a frame structure (sometimes referred to as pole-pieces). The magnet units are either glued to the frame structure or clamped to it by a locking structure. One ribbon speaker of this type is disclosed in WO 99/55118, which is incorporated herein in its entirety by reference. As disclosed in WO 99/55118, electro-acoustic transducers of this type can, further, comprise two or more gaps with one membrane in each gap.

Another approach is to provide self-supporting elongated magnet elements, as disclosed in WO 96/07294 and US 4,049,926. However, such elongated magnet units tend to become very expensive and they are furthermore relatively fragile.

Ribbon speakers are normally considered to be high-cost speakers. This is mainly due to the large amount of magnetic material used, the relatively com- plex assembly procedure, and the small production volumes. Further, as a result of the magnetic material and because the pole pieces normally are made of iron, ribbon speakers tend to become quite heavy, which make them less attractive for use in mobile PA-systems. Another shortcoming concerning their use in mobile PA-systems, is that they tend to be quite fragile as the magnets which normally are glued to the frame structure might relatively easy come loose.

Summary of the invention

The object of the present invention therefore is to provide an electro-acoustic transducer of ribbon type, which is lightweight, easier to assemble, more robust and cheaper to produce, compared with the prior art transducers. This object of the invention has been achieved by the invention as defined in claim 1.

In the electro -acoustic transducer of ribbon type according to the invention the pole pieces are omitted and the magnet units are supported in longitudinal supporting profiles of a non-ferro-magnetic material, whereby the magnet units are more securely supported, and the mounting and positioning of the magnet units is simplified.

In one preferred embodiment of the invention, the frame unit comprising the longitudinal supporting profiles may be extruded as a unitary structure, the electro-acoustic transducer can thus be made extremely rigid and robust, while the production costs still are kept low.

In another preferred embodiment of the invention, the frame unit comprising the longitudinal supporting profiles is moulded, and the magnet units are placed in the mould prior to the injection of the casting material, such that the magnet units become permanently affixed in the longitudinal supporting profiles. The production costs is thus further reduced, as the assembly process will involve a minimum of parts.

Another object is to provide a method of manufacturing an electro-acoustic transducer of ribbon type as described above. This method involves less manufacturing steps and the step of mounting the magnets is greatly simplified, compared with the prior art. This object of the invention has been achieved by the invention as defined in claim 25. A third object of the present invention is to provide a loudspeaker system comprising an electro-acoustic transducer of ribbon type, which loudspeaker system fully utilises the benefits of the electro-acoustic transducer presented herein. This object of the invention has been achieved by the invention as defined in claim 21.

Such a loudspeaker system may be designed by integrating the frame unit of the electro-acoustic transducer in the loudspeaker front baffle or enclosure.

Brief description of the drawings

The invention will now be described with reference to the attached drawing figures, wherein:

Fig. la is shows a prior art ribbon speaker unit in perspective view.

Fig. lb is a top-view of the prior art ribbon speaker unit.

Fig. 2a is a schematic perspective view of an electro-acoustic transducer according to the invention seen from the back.

Fig. 2b is a top view of an electro-acoustic transducer according to the invention.

Fig. 3a is a top view of one possible shape of the cross-section of the longitudinal supporting profiles.

Fig. 3b is a top view of one possible shape of the cross-section of the longitudinal supporting profiles.

Fig. 3c is a top view of one possible shape of the cross- section of the longitudinal supporting profiles.

Fig. 4 is a close up perspective view of a support portion. Fig. 5a is a perspective view of an unmachined extruded profile used in one embodiment.

Fig. 5b is a perspective view of the extruded profile in fig. 5a after it is machined.

Fig 6a is a top view of one embodiment of the invention with an integrated resonance cavity.

Fig 6b is an exploded perspective view of one embodiment of the invention with an integrated resonance cavity.

Fig. 7 illustrates an embodiment having four support profiles.

Fig. 8a illustrates an embodiment with a semi-cylindrical shape which has five support profiles.

Fig. 8b illustrates an embodiment with a cylindrical shape which has fifteen support profiles.

Fig. 9a illustrates an embodiment where three membranes share the same rear cavity.

Fig. 9b illustrates an embodiment where three membranes have separate rear cavities.

Fig. 10a illustrates an embodiment wherein one electro-acoustic transducer according to the invention is integrated with a front baffle of a loudspeaker system.

Fig. 10b illustrates an embodiment wherein one electro-acoustic transducer according to the invention is integrated with an enclosure of a loudspeaker system.

Detailed description of the embodiments

A conventional ribbon speaker unit is shown in figures la and lb. This ribbon speaker unit 1 comprises two or more elongated pole pieces 2a, 2b arranged in par- allel with each other and spaced apart from each other, comprising magnet units 3a, 3b. Two adjacent pole pieces 2a, 2b form an elongated slit in which an elongated electrically conducting membrane 4 is moveably provided, said membrane 4 being electrically coupled such that a drive current can be passed in the longitudinal direction thereof. In this particular ribbon speaker, the magnets are glued in position on the pole pieces 2a, 2b.

The electro-acoustic transducer of ribbon type shown in the drawing figures 2a and 2b comprises one elongated frame unit 10, comprising two longitudinal supporting profiles 1 la, 1 lb of a non-ferro-magnetic material, between which there is formed a gap 12, in which there is provided an elongated, thin, ribbon- shaped membrane 13. The magnet assembly of the electro-acoustic transducer comprises the longitudinal supporting profiles 1 1a, 1 lb, in which there are provided magnet units 14, said magnet units 14 being arranged with a pole of one polarity of a first magnet unit 14 facing a pole of opposite polarity of a second magnet unit 14. The elongated frame unit 10 further comprises a top clamping unit 15a and a bottom clamping unit 15b, which both comprise closure units 17a, 17b for the longitudinal supporting profiles 1 1a, l ib, such that the magnet units 14 arranged therein are supported and arrested in all directions, and such that the elongated frame unit 10 becomes a rigid unit.

The membrane 13 is clamped in the gap 12 between the longitudinal supporting profiles 1 1a, 1 lb by the top clamping unit 15a and the bottom clamping unit 15b, without being so stretched in its longitudinal direction that the motion of the membrane 13 caused by a current running in longitudinal direction of the membrane is affected. The elongated frame unit 10 may have a substantial length e.g. up to 2 meters or more depending on the purpose.

The cross- sections of the longitudinal supporting profiles 1 1a, l ib are shaped such that the magnet units 14 are supported and arrested therein, and they may be closed, open or partially open. Examples of suitable cross-section shapes are shown in fig. 3a-3c. Further, the longitudinal supporting profiles 1 1a, 1 lb are designed such that only a small amount of material or no material is present between the magnet units 14 and the membrane 13, to achieve as high magnetic flux as possible in the gap 12. To prevent the magnet units 14 from vibrating in the longitudinal supporting profiles 11a, l ib, they can be further affixed by the addition of an adhesive substance, which may completely fill the space between the magnet units 14 and the longitudinal supporting profiles 1 la, 1 lb, such as epoxy resin or silicone rubber. The magnet units 14 comprise at least one permanent magnet or electromagnet. The closure units 17a, 17b may also be provided separate from the top clamping unit 15a and the bottom clamping unit 15b.

The membrane 13 has a somewhat smaller width than the width of the gap 12, and is provided to be centered between the longitudinal supporting profiles 1 1a, 1 lb. The membrane 13 typically is 2 mm narrower than the width of the gap 12. The membrane 13 preferably comprises a body of polymeric material, such as MYLAR® or KAPTON® and the like, which is provided with at least one surface layer of an electrically conducting material, e.g. aluminium, which may be deposited by evaporation or laminated thereto. The thickness of the membrane 13 is very small, e.g. of the order of 5 - 30 μm including the surface layer. The membrane 13 has a width of the order of 10 - 50 mm, and a length corresponding to the length of the elongated frame unit 10. The membrane 13 can also be comprised of a homogenous metal band, e.g. of copper, aluminium or silver. As previously is known, the membrane 13 could be pleated across its longitudinal direction, or have an imprinted pattern, e.g. of a honeycomb or leather structure.

If in addition the membrane 13 has a large length it can also be necessary to further provide transverse beamlike support portions 18 between the longitudinal supporting profiles 11a, l ib at intervals along their length. Further, the support portions 18 provide support between the longitudinal supporting profiles 11a, 1 lb of the frame unit 10. The support portions 18 may be fastened to the longitudinal supporting profiles 1 1a, 1 lb in several suitable ways, such as by screws, rivets, welding.

Fig. 4 is a close up view of one support portion 18, which bridges the gap 12. The membrane 13 is clamped to the support portion 18 by a support clamping unit 21. If the support portion 18 and /or the support clamping unit 21 are made of an electrically conducting material, an insulating unit 22 prevents electrical contact between the conducting membrane 13 and the support portion 18 and the clamping unit 21. The support clamping unit 21 is preferably fastened to the support portion 18 by one or more screws, but it may be fastened by other means, such as rivets, snap-lock structures or the like. The longitudinal supporting profiles 11a, l ib and the support portions 18 are preferably integrated with the frame unit 10. The frame unit 10 is preferably manufactured as an extruded profile, whereby a suitable material is extruded through a dye with the desired shape. Suitable materials are for example aluminium and other lightweight alloys, as well as polymeric and composite materials.

An example of an extruded profile where the longitudinal supporting profiles 1 la, 1 lb and the support portions 18 are integrated with the frame unit 10, is shown in figs. 5a and 5b. As shown in fig. 5a excess material between the integrated support portions 18, has to be removed from the extruded profile by a machining procedure. In fig. 5b the profile is shown, after the removal of the excess material between the integrated support portions 18.

Once the extruded frame unit 10 is produced, it is cut into the desired length and the bottom clamping unit 15b is mounted on one end of the extruded frame unit 10. Thereafter the magnet units 14 are placed in the longitudinal supporting profiles 1 la, 1 lb, arranged with opposite poles on either side of the gap 12. An adhesive substance is preferably added to prevent the magnets from vibrating. The top clamping unit 15a is then mounted on the other end of the extruded frame unit 10, and the elongated, thin, ribbon-shaped membrane 13 is clamped between the top clamping unit 15a and the bottom clamping unit 15b, such that it is arranged in the gap 12 between the longitudinal supporting profiles 1 1a, l ib. Finally, if support portions 18 are present, the support clamping units 21 are mounted.

Compared to the ribbon speaker unit disclosed in WO 99/55118, where the magnet units 3a, 3b have to be glued to the pole pieces 2a, 2b, the assembly process for the ribbon speaker unit according to the present invention is significantly facilitated. Furthermore, as the heavy pole pieces 2a, 2b are omitted the total weight of the ribbon speaker unit is reduced.

Alternatively, the frame unit 10 can be moulded. In a special embodiment of this kind, the magnet units 14 may be arranged in position in the mould prior to the injection of the casting material, such that the magnet units 14 become permanently affixed in the longitudinal supporting profiles 11a, 1 lb. This embodiment is extremely cheap to produce, and it is very suitable for large-scale production. In a further embodiment of this kind the top clamping unit 15a and the bottom clamping unit 15b are integrated in the frame unit 10, whereby the assembly process will involve even less parts.

In one embodiment of the invention, which is shown in fig. 6, the frame unit 10 further comprises a rear cavity 30 formed by a rear wall portion 31 connecting the two longitudinal supporting profiles 11a, l ib along the whole of their length, and a rear cavity top cover 32a and a rear cavity bottom cover 32b. This rear cavity 30 protects the membrane 13 in situations when the atmospheric pressure suddenly changes. The rear cavity 30 may also be used as a resonance cavity if suitably dimensioned, whereby the low frequency response of the ribbon speaker unit may be enhanced. The rear wall portion 31 is preferably integrated with the frame unit 10 in such a manner that only the rear cavity top cover 32a and the rear cavity bottom cover 32b have to be arranged at the top and bottom respectively. Said rear cavity top cover 32a and rear cavity bottom cover 32b may further be integrated with the top clamping unit 15a and the bottom clamping unit 15b, respectively. The shape of the rear cavity 30 should essentially be such that parallel surfaces do not occur, in order to reduce the risk for standing waves in the cavity. The ribbon speaker unit with the rear cavity 30 further, becomes extremely rigid, especially if integrated support portions 18 are present.

In figure 7 there is shown an embodiment with four longitudinal supporting profiles 11 forming three gaps 12, in each of which there is provided one membrane 13, respectively. In fig. 8a a similar embodiment is shown where the four ribbon membranes represent a semi- cylindrical radiating source, and in fig. 8b an embodiment of a cylindrical radiating source with fifteen ribbon membranes is shown. Embodiments of this type, with two or more membranes, may further comprise one or more rear cavities 30, such that several membranes share the same rear cavity 30, or that all membranes have their own rear cavity 30, as shown in fig. 9a and 9b, respectively.

The ribbon speaker unit 40 according to the present invention may further be integrated with a front baffle 41 of a speaker system, as shown in fig. 10a, wherein one or more low frequency speaker units 42 are mounted in the baffle together with the ribbon speaker unit 40. As shown in fig. 10b, the loudspeaker enclosure 43 may also be integrated with the ribbon speaker unit 40. In this way, a complete system is designed using as few parts as possible.

Above a number of embodiments have been described. However, it is obvious that the design of the frame unit or corresponding elements as well as the design of the longitudinal supporting profiles could be varied without deviating from the inventive idea, that is to provide an electro-acoustic transducer of ribbon type, which is lightweight, easier to assemble, more robust and cheaper to produce, compared with the prior art transducers.

Therefore the present invention should not be regarded as restricted to the above disclosed embodiments, but can be varied within the scope of the appended claims.

Claims

1. An electro-acoustic transducer comprising a frame unit (10), at least two elongated magnet units (14), and at least one electrically conducting elongated membrane (13), wherein

the frame unit (10) comprises at least two longitudinal supporting profiles (1 la, 1 lb) of a non-ferro-magnetic material,

the longitudinal supporting profiles (11a, 1 lb) are arranged in parallel with each other and spaced apart from each other, whereby two adjacent longitudinal supporting profiles (11a, l ib) form an elongated gap (12),

the frame unit (10) further comprises one or more support portions (18) for supporting the membrane (13), said support portions (18) being arranged between the longitudinal supporting profiles (1 1a, 1 lb) and distributed along their length

the magnet units (14) are supported by the longitudinal supporting profiles (1 la, 1 lb) and at least partially enclosed by said profiles such that the magnet units (14) are interlocked therein, and arranged with a pole of one polarity of a first magnet unit (14) facing a pole of opposite polarity of a second magnet unit (14),

the electrically conducting elongated membrane(s) (13) are provided in said gap(s) (12),

the membrane (13) is electrically coupled to enable the passing of a drive current in the longitudinal direction of the membrane (13), and

characterized in that the longitudinal supporting profiles (Ha, l ib) and the support portions (18) are integrated with the frame unit (10) to form a unitary structure.

2. The electro-acoustic transducer according to claim 1, characterized in that the cross-sections of the longitudinal supporting profiles (1 1a, 1 lb) are closed.

3. The electro-acoustic transducer according to claim 1 or 2, characterized in that the frame unit (10) further comprises at least one rear wall portion (31) interconnecting at least the two outermost longitudinal supporting profiles (1 1a, l ib) along the whole of their length, and a rear cavity top cover (32a) and a rear cavity bottom cover (32b) arranged to close a cavity (30) formed by said rear wall portion (31) at the top and bottom, respectively.

4. The electro-acoustic transducer according to claim 3, characterized in that the cavity (30) is a resonance cavity.

5. The electro-acoustic transducer according to claim 3 or 4, characterized in that the rear wall portion(s) (31) is/ are integrated with the frame unit (10) to form a unitary structure.

6. The electro-acoustic transducer according to any of the claims 1 to 5, characterized in that the frame unit (10) is arranged such that two or more membranes (13) face in different horizontal directions, so as to form a semi-cylindrical or a cylindrical radiating source.

7. The electro-acoustic transducer according to any of the claims 1 to 6, characterized in that the frame unit (10) is an extruded profile.

8. The electro-acoustic transducer according to any of the claims 1 to 6, characterized in that the frame unit (10) is a moulded structure.

9. The electro-acoustic transducer according to claim 8, characterized in that the magnet units (14) are integrated in the moulded structure.

10. The electro-acoustic transducer according to claims 8 or 9, characterized in that a top clamping unit (15a) and a bottom clamping unit (15b) are integrated in the moulded structure.

1 1. A loudspeaker system, characterized in that it comprise at least one electro-acoustic transducer according to any of the claims 1 to 10.

12. The loudspeaker system according to claim 1 1, characterized in that the frame unit(s) (10) of the electro-acoustic transducer(s) are integrated in a front baffle (41) of the loudspeaker system.

13. The loudspeaker system according to claim 1 1, characterized in that the frame unit(s) (10) of the electro-acoustic transducer(s) are integrated in the loudspeaker system enclosure.

14. Method of manufacturing an electro-acoustic transducer, comprising the steps of:

providing, as a unitary structure, a frame unit (10) comprising at least two longitudinal supporting profiles (Ha, l ib), and one or more support portions (18) being arranged between the longitudinal supporting profiles (1 1a, l ib) and distributed along their length,

arranging magnet units (14) in said longitudinal supporting profiles (1 la, 1 lb), such that the magnet units (14) are supported by the longitudinal supporting profiles (1 la, 1 lb) and at least partially enclosed by the profiles, said magnet units (14) being arranged with a pole of one polarity of a first magnet unit (14) facing a pole of opposite polarity of a second magnet unit (14), and

attaching elongated, thin, ribbon-shaped membrane (13) in the gap (12) between two adjacent longitudinal supporting profiles (1 la, 1 lb).

15. Method according to claim 14, further comprising the steps of:

providing at least one rear wall portion (31) interconnecting at least the two outermost longitudinal supporting profiles (11a, 1 lb) along the whole of their length,

providing a rear cavity top cover (32a) and a rear cavity bottom cover (32b), and arranging said rear cavity top cover (32a) and said rear cavity bottom cover (32b) to close a cavity (30) formed by said rear wall portion (31), at the top and bottom, respectively.

16. Method according claim 14 or 15, characterized in that the frame unit (10) and the rear wall portion (31) are provided as a unitary structure.

17. Method according to any of the claims 14 to 16, characterized in that the step of providing the frame unit (10) is performed by the steps of:

extruding a unmachined extruded frame unit profile, and

removing excess material between the integrated support portions 18, from the extruded profile by a machining procedure.

18. Method according to any of the claims 14 to 16, characterized in that the frame unit (10) is provided by moulding.

19. Method for producing an electro-acoustic transducer, comprising the steps of:

providing a mould for a frame unit (10), comprising sections representing two or more longitudinal supporting profiles (11a, l ib), arranging a magnet unit (14) in the mould at each said section representing the longitudinal supporting profile (1 la, 1 lb), said magnet units (14) being arranged with a pole of one polarity of a first magnet unit (14) facing a pole of opposite polarity of a second magnet unit (14),

injecting casting material into the mould, and

attaching an elongated, thin, ribbon-shaped membrane (13) in the gap (12) between the longitudinal supporting profiles (Ha, l ib).