Magnetic circuit

Abstract

A magnetic circuit (100) configured for use in a dual membrane driver (200) is presented. The magnetic circuit (100) comprises a first substantially cylindrically formed magnet arrangement (110) having a north pole (111) facing in a first direction (110'), the first magnet arrangement (110) being concentric with a first axis (X) and a second substantially cylindrically formed magnet arrangement (120) having a north pole (121) facing in a second direction (120') being different from the first direction (110'). The second magnet arrangement (120) is concentric with the first axis (X) and arranged radially and / or axially distanced from the first magnet arrangement (110) such that a first partial magnetic circuit (100a) is formed from the north pole (111) of the first magnet arrangement (110) to a south pole (122) of the second magnet arrangement (120) and a second partial magnetic circuit (100b) is formed from the north pole (121) of the second magnet arrangement (120) to a south pole (112) of the first magnet arrangement (110). The magnetic circuit (100) further comprises a first voice coil (141) concentric with the first axis (X) within the first partial magnetic circuit (100a), and a second voice coil (142) concentric with the first axis (X) within the second partial magnetic circuit (100b).

Description

[0001] MAGNETIC CIRCUIT

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to transducers, and specifically acoustic transducers.

[0004] BACKGROUND

[0005] Speakers are typically either loud or small, especially when it comes to bass performance. Designing speakers with strong bass response requires careful consideration of multiple factors, including acoustic performance, size, distortion, power handling, room acoustics, compatibility, cost, aesthetics etc. Generating powerful bass requires moving large amounts of air. To achieve this, speakers with larger drivers or multiple drivers may be necessary. However, increasing the size of the speaker and the enclosure can lead to practical limitations, as it may make the speaker bulky or difficult to integrate into different environments.

[0006] Further to this, moving large amounts of air induces vibrations in a structure of the speaker. Reducing these vibrations is challenging, costly and generally require a significant amount of volume, which may compromise design of the speaker.

[0007] SUMMARY

[0008] It is in view of the above considerations and others that the various embodiments of this disclosure have been made. The present disclosure therefore recognizes the fact that there is a need for alternatives to (e.g. improvement of) the existing art described above. It is an object of some embodiments to solve, mitigate, alleviate, or eliminate at least some of the above or other disadvantages.

[0009] An object of the present invention is therefore to provide a new type of magnetic circuit for an acoustic transducer which is improved over the prior art, which eliminates or at least mitigates one or more of the drawbacks discussed above. More specifically, an object of embodiments of the present invention is to provide a magnetic circuit for a dual opposing membrane acoustic driver that allows for a compact design using mainly standard components. These objects are achieved by a technique as set forth in the appended independent claims with advantageous embodiments defined in the dependent claims related thereto.

[0010] In a first aspect, a magnetic circuit configured for use in a dual membrane driver is presented. The magnetic circuit comprises a first substantially cylindrically formed magnet arrangement having a north pole facing in a first direction. The first magnet arrangement is concentric with a first axis. The magnetic circuit further comprises a second substantially cylindrically formed magnet arrangement having a north pole facing in a second direction that is different from the first direction, the second magnet arrangement is concentric with the first axis and arranged radially and / or axially distanced from the first magnet arrangement such that a first partial magnetic circuit is formed from the north pole of the first magnet arrangement to a south pole of the second magnet arrangement, and a second partial magnetic circuit is formed from the north pole of the second magnet arrangement to a south pole of the first magnet arrangement. The magnetic circuit further comprises a first voice coil concentric with the first axis within the first partial magnetic circuit, and a second voice coil concentric with the first axis within the second partial magnetic circuit.

[0011] In some variants, an outer diameter of the second voice coil is smaller than an inner diameter of the first voice coil. This is beneficial as the maximum allowable excursion, i.e. axial movement of the voice coils is increased.

[0012] In some variants, an outer diameter of the second magnet arrangement is smaller than an inner diameter of the first magnet arrangement such that an annular space extending at least partly through the magnetic circuit along the first axis is formed, wherein the first partial magnetic circuit and the second partial magnetic circuit are at least partly within the annular space. This is beneficial as it allows for a more compact design and significantly reduces stray magnetic fields.

[0013] In some variants, at least one of the first magnet arrangement or the second magnet arrangement is an axially magnetized magnet, wherein a magnetic pole member is connected to the north pole or the south pole of the at least one axially magnetized magnet. This is beneficial as the magnetic pole member assist in controlling the magnetic field and increases the magnetic flux at the magnet gap, i.e. the air gaps of the partial magnetic circuits. In some variants, the magnetic pole member is arranged to extend into the annular space. This is beneficial as it reduces the air gaps of the partial magnetic circuits and thereby increase the magnetic flux at the magnet gaps.

[0014] In some variants, both the first magnet arrangement and the second magnet arrangement are axially magnetized magnets. A first magnetic pole member is connected to the north pole or the south pole of the first magnet arrangement, and wherein a second magnetic pole member is connected to the corresponding one of the north pole or the south pole of the second magnet arrangement. This is beneficial as the magnetic pole member assist in controlling the magnetic field and increase the magnetic flux at the magnet gap, i.e. the air gaps of the partial magnetic circuits.

[0015] In some variants, the second magnet arrangement is arranged at least partly inside the first magnet arrangement along the first axis, and wherein the first voice coil is arranged radially outside of the second magnetic pole member, and wherein the second voice coil is arranged radially inside of the first magnetic pole member. This is beneficial as it allows for a more compact design and significantly reduced stray magnetic fields.

[0016] In some variants, the magnetic circuit further comprising a cylinder concentrically with the first axis and being arranged to connect the first magnetic pole member to the second magnetic pole member dividing the annular space in a first annular subspace between the first magnet arrangement and the cylinder and a second annular subspace between the cylinder and the second magnet arrangement. The first voice coil is arranged inside the first annular subspace and the second voice coil is arranged inside the second annular subspace. This is beneficial as the cylinder provides mechanical support for the magnetic circuit.

[0017] In some variants, the cylinder is a magnetic cylinder. This is beneficial as the magnetic cylinder will assists in controlling the magnetic field and increasing the magnetic flux at the magnet gap, i.e. the air gaps of the partial magnetic circuits.

[0018] In some variants, the cylinder is an electrically conducting cylinder. This is beneficial as the electrically conducting cylinder improves inductance of the voice coils.

[0019] In some variants, one of the first magnet arrangement or the second magnet arrangement is a radially magnetized magnet, and a cylinder is connected to the north pole or the south pole of the radially magnetized magnet and arranged concentrically with first axis inside the annular space dividing the annular space in a first annular subspace between the first magnet arrangement and the cylinder and a second annular subspace between the cylinder and the second magnet arrangement. The first voice coil is arranged inside the first annular subspace and the second voice coil is arranged inside the second annular subspace. Radial magnet arrangements are beneficial as they enable more efficient usage of the magnet material as magnetic fields need less routing.

[0020] In some variants, both the first magnet arrangement and the second magnet arrangement are radially magnetized magnets. Radial magnet arrangements are beneficial as they enable more efficient usage of the magnet material as magnetic fields need less routing.

[0021] In some variants, the cylinder is connected to the magnetic pole member. This is beneficial as the cylinder provides mechanical support for the magnetic circuit.

[0022] In some variants, an outer diameter of the second magnet arrangement is substantially equal to an outer diameter of the first magnet arrangement and / or an inner diameter of the second magnet arrangement is substantially equal to an inner diameter of the first magnet arrangement, wherein both the first magnet arrangement and the second magnet arrangement are radially magnetized magnets. This is advantageous as it significantly reduces stray magnetic fields.

[0023] In a second aspect, a dual membrane driver is presented. The dual membrane driver comprises a magnetic circuit of the first aspect, a first membrane being concentric with the first axis of the magnetic circuit, a second membrane being concentric with the first axis of the magnetic circuit and facing in an opposite direction of the first membrane. The first membrane is connected to the first voice coil and the second membrane is connected to the second voice coil.

[0024] In a third aspect, a speaker comprising the dual membrane driver according to the second aspect is presented. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Embodiments of the invention will be described in the following text; references being made to the appended diagrammatical drawings which illustrate nonlimiting examples of how the inventive concept can be reduced into practice.

[0026] Fig. l is a view of an exemplary magnetic circuit;

[0027] Fig. 2 is a cross-sectional side view of an exemplary magnetic circuit according to some variants of the present disclosure;

[0028] Fig. 3 A is a top planar view of an exemplary magnetic circuit according to some variants of the present disclosure;

[0029] Fig. 3B is a top planar view of an exemplary magnetic circuit according to some variants of the present disclosure;

[0030] Fig. 3C is a cross-sectional side view of the magnetic circuit in Fig, 3A;

[0031] Fig. 4 is a cross-sectional side view of an exemplary magnetic circuit according to some variants of the present disclosure;

[0032] Fig. 5 is a cross-sectional side view of an exemplary magnetic circuit according to some variants of the present disclosure;

[0033] Fig. 6 is a cross-sectional partial side view of an exemplary magnetic circuit according to some variants of the present disclosure;

[0034] Fig. 7 is a cross-sectional partial side view of an exemplary magnetic circuit according to some variants of the present disclosure;

[0035] Fig. 8 is a cross-sectional partial side view of an exemplary magnetic circuit according to some variants of the present disclosure;

[0036] Fig. 9 is a cross-sectional partial side view of an exemplary magnetic circuit according to some variants of the present disclosure;

[0037] Fig. 10 is a cross-sectional side view of an exemplary dual membrane driver according to some variants of the present disclosure;

[0038] Fig. 11 is a cross-sectional side view of an exemplary dual membrane driver according to some variants of the present disclosure;

[0039] Fig. 12A is front planar view of an exemplary speaker according to some variants of the present disclosure;

[0040] Fig. 12B is a back planar view of the speaker in Fig. 12A. DETAILED DESCRIPTION OF EMBODIMENTS

[0041] Hereinafter, certain embodiments will be described more fully with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention, such as it is defined in the appended claims, to those skilled in the art.

[0042] The term “coupled” is defined as connected, although not necessarily directly, and not necessarily mechanically. Similarly, the term “connected”, or “operatively connected”, is defined as connected, although not necessarily directly, and not necessarily mechanically. Two or more items that are “coupled” or “connected” may be integral with each other. The terms “a” and “an” are defined as one or more unless this disclosure explicitly requires otherwise. The terms “substantially”, “approximately” and “about” are defined as largely, but not necessarily wholly what is specified, as understood by a person of ordinary skill in the art. The terms “comprise” (and any forms thereof), “have” (and any forms thereof), “include” (and any form thereof) and “contain” (and any forms thereof) are open-ended linking verbs. As a result, a method that “comprises”, “has”, “includes” or “contains” one or more steps, possesses those one or more steps, but is not limited to possessing only those one or more steps.

[0043] As previously indicated, when designing speakers with strong bass response, there are several challenges that engineers and designers generally face. Generating powerful bass requires moving large amounts of air. To achieve this, speakers with larger drivers or multiple drivers may be necessary. However, increasing the size of the speaker and the enclosure may lead to practical limitations, as it may make the speaker bulky or difficult to integrate into different environments. Further to this, providing deep and impactful bass without compromising the overall frequency response can be challenging. It requires careful tuning of the driver, enclosure, and crossover components to ensure a smooth transition between the bass and midrange frequencies. Additionally, controlling distortion at high sound pressure level (SPL) is crucial, as excessive distortion can degrade the overall audio quality. Also, bass frequencies require more power compared to other frequencies due to the extended movement of membranes at low frequencies. This means that designing of speakers with strong bass response requires considering power handling capabilities and ensuring that the driver, voice coil, and amplifier can handle the increased load without introducing distortion or damage. In addition, designing speakers with strong bass response often involves the use of specialized components, such as larger drivers, robust enclosures, and advanced amplifiers. These components may increase manufacturing cost and lead times, making it challenging to strike a balance between performance and affordability. If the above was not enough, integrating powerful bass response into a visually appealing and compact form factor may be a challenge. Balancing the acoustic requirements with the design constraints, especially for portable or compact speaker systems, is a complex task.

[0044] The inventors behind the present disclosure have, through inventive thinking and challenging of the technical prejudice in speaker design, realized that by designing a dual membrane driver as one single magnetic circuit, at least some of the shortcomings and / or problems with the prior art are solved or at least reduced.

[0045] As will be explained in the following, the present disclosure relates to use of at least two magnets, with different magnetic orientation, to steer magnetic fields more efficiently to the desired locations (two magnet gaps). The two magnets are concentrically arranged and by doing this, a very compact and lightweight dual membrane driver is provided. The dual membrane driver will exhibit a strong force factor for two similar opposed membranes. It may be described as nesting two drivers in the same space, which, due to their common magnetic circuit, increases the efficiency of the respective magnetic circuits of each driver. As the magnet gaps are concentric, it is possible to use standard suspension solutions and voice coils which leads to fast prototyping for new driver designs.

[0046] For the present disclosure, magnetic circuits will be used as a framework to describe a flow of magnetic fields through various components and materials. It may be considered an analogy to an electrical circuit, where magnetic flux takes the place of electric current. In a magnetic circuit, magnetic flux is generated by a magnetic source. This flux flows through a closed path, known as the magnetic circuit, which may comprise different elements. These elements comprise ferromagnetic materials, air gaps, magnetic cores etc. For the present disclosure, the main components of a magnetic circuit are a magnetic source and an air gap. The magnetic source is a permanent magnet (magnet for short) and the air gap is a space or a region intentionally provided to facilitate the interaction with other components (e.g. voice coils). In some examples and embodiments, further components may form part of the magnetic circuit.

[0047] As is commonly known to the skilled person, behaviours of magnetic circuits are governed by fundamental principles, including Ampere's law, Faraday's law of electromagnetic induction, and the concept of magnetic flux. As mentioned, the magnetic flux is analogous to electric current, and just as electric circuits have resistance, magnetic circuits have reluctance. Reluctance is a measure of the opposition to the flow of magnetic flux and depends on the materials and dimensions of the magnetic circuit components. A magnetic circuit may be characterized by parameters such as magnetic flux, magnetic field strength, magnetomotive force (MMF), and magnetic flux density. These parameters are interconnected and may be described using mathematical equations, such as the magnetic circuit laws or the B-H curve, which relates the magnetic flux density (B) to the magnetic field strength (H) in a material.

[0048] In Fig. 1 an exemplary magnetic circuit 100 is shown. In Fig. 1, the magnetic circuit 100 is formed by a first magnet arrangement 110 and a second magnet arrangement 120. The first magnet arrangement 110 and the second magnet arrangement 120 are magnetic sources of the magnetic circuit 100. The first magnet arrangement 110 and the second magnet arrangement are separated by an air gap. The first magnet arrangement 110 comprises a north pole 111 and an opposite south pole 112. The north pole 111 of the first magnet arrangement 110 is arranged to face in a first direction 110’. Correspondingly, the second magnet arrangement 120 comprises a north pole 121 and an opposite south pole 122. The north pole 121 of the second magnet arrangement 120 is arranged to face in a second direction 120’. In Fig. 1, the first direction 110’ is opposite the second direction 120’. As a result of the opposite directions 110’, 120’, the magnetic circuit 100 is formed by a first partial magnetic circuit 110a between the north pole 111 of the first magnet arrangement 110 and the south pole 122 of the second magnet arrangement 120, and a second partial magnetic circuit 110b between the north pole 121 of the second magnet arrangement 120 and the south pole 112 of the first magnet arrangement 110. The first partial magnetic circuit 110a will comprise an air gap with a magnetic field (indicated by an arrow in Fig. 1) from the north pole 111 of the first magnet arrangement 110 to the south pole 122 of the second magnet arrangement 120. Correspondingly, the second magnetic circuit 110b will comprise an air gap with a magnetic field (indicated by an arrow in Fig. 1) from the north pole 121 of the second magnet arrangement 120 to the south pole 112 of the first magnet arrangement 110.

[0049] In the following, the north poles 111, 121 and the south poles 112, 122 will not be shown in the figures for reasons of clarity. Rather, the direction 110’, 120’ of the magnetization, i.e. the direction the north pole 111, 121, is facing will be shown. The skilled person will understand that the directions 110’, 120’ indicated are from a south pole 112, 122 to a north pole 111, 121 of the associated magnet arrangement 110, 120.

[0050] For the present disclosure, a magnet arrangement 110, 120 is an arrangement that comprise at least one magnet. In magnet arrangements 110, 120 comprising more than one magnet, all magnets will have a common magnetization direction and be arranged sufficiently close to each other such that the magnet arrangement 110, 120 will form one magnetic source in a magnetic circuit. In the following examples, the magnet arrangements 110, 120 are substantially cylindrically formed which means that the magnet arrangement 110, 120 may be formed by one single cylindrical magnet, or by a plurality of magnets arranged to for a substantially cylindrical magnet arrangement. A shape of the individual magnets forming a magnet arrangement 110, 120 may be any suitable shape. In some examples, a cross section of the individual magnets forming a magnet arrangement 110, 120 may be cylindrical, elliptical, square, rectangular, tetrahedral, or combinations thereof.

[0051] If Fig. 2 a cross-section of a magnetic circuit 100 is shown. The magnetic circuit 100 comprises a first magnet arrangement 110 and a second magnet arrangement 120. Both the first magnet arrangement 110 and the second magnet arrangement 120 are substantially cylindrical magnet arrangements 110, 120. The first magnet arrangement 110 and the second magnet arrangement 120 are arranged concentric with a first axis X. In Fig. 2, the first magnet arrangement 110 is substantially identical to the second magnet arrangement 120 when it comes to size, shape and magnetic field strength (magnetic flux density). Both magnet arrangements 110, 120 are radially magnetized. Radially magnetized magnet arrangements 110, 120 are advantageous as they enable a more efficient usage of the magnet material as magnetic fields requires less routing. The first direction 110’ of the first magnet arrangement 110, i.e. the direction in which the north pole 111 (not indicated in Fig. 2) of the first magnet arrangement 110 is facing, is towards the first axis X, i.e. inwards. The second direction 120’ of the second magnet arrangement 120, i.e. the direction in which the north pole 121 (not indicated in Fig. 2) of the second magnet arrangement 120 is facing, is away from the first axis X, i.e. outwards. In other words, the first direction 110’ and the second direction 120’ are different, and in Fig. 2, opposite. Due to the opposite directions 110’, 120’, as in Fig. 1, the first partial magnetic circuit 100a is provided between the north pole 111 of the first magnet arrangement 110 and the south pole 122 of the second magnet arrangement 120. This places the first partial magnetic circuit 110a inside the first and second magnet arrangements 110, 120. The second partial magnetic circuit 100b is provided between the north pole 121 of the second magnet arrangement 120 and the south pole 112 of the first magnet arrangement 110. This places the second partial magnetic circuit 110b outside the first and second magnet arrangements 110, 120. A first voice coil 141, concentric with the first axis X is arranged within the first partial magnetic circuit 100a. A second voice coil 142 concentric with the first axis X is arranged within the second partial magnetic circuit 100b. In Fig. 2, the first voice coil 141 is arranged radially inside the first and second cylindrical magnet arrangements 110, 120 and movable along the first axis X throughout the full axial extension of an air gap of the first partial magnetic circuit 100a. Similarly, in Fig. 2, the second voice coil 142 is arranged radially outside the first and second cylindrical magnet arrangements 110, 120 and movable along the first axis X throughout the full axial extension of an air gap of the second partial magnetic circuit 100b.

[0052] It should be mentioned that both the first voice coil 141 and the second voice coil 142 may be arranged in the same partial magnetic circuit 100a, 100b. The arrangement shown in Fig. 2 is advantageous as the axial movement (excursion capability) of the voice coils 141, 142 is not hindered by the other voice coil 141, 142. If, for instance, both voice coils 141, 142 are driven towards each other, the voice coils 141, 142 would collide and their respective axial movements would be limited. The voice coils 141, 142 may be driven in opposite phases to avoid this, such that the voice coils 141, 142 would move in the same axial direction. However, such a setup would significantly reduce the amount of sound pressure produced and cause severe vibrations as reaction forces of membranes connected to the voice coils 141, 142 will not cancel each other out but rather oscillate in unison. Although the example of Fig. 2 is advantageous, the other examples given above are nonetheless to be considered working embodiments of the present disclosure.

[0053] With reference to Figs. 3 A-C an exemplary embodiment will be presented wherein the first and second cylindrical magnet arrangements 110, 120 are formed with different diameters such that one of the first or second cylindrical magnet arrangements 110, 120 fits radially inside the other of first and second cylindrical magnet arrangement 110, 120. In Fig. 3A, a top view of a magnetic circuit 100 is shown. In Fig. 3A, an inner diameter 1 lOi of the first magnet arrangement 110 is greater than an outer diameter 120o of the second magnet arrangement 120. In Fig. 3A, a radial width of the first magnet arrangement 110, i.e. a difference between an outer diameter 1 lOo and the inner diameter 1 lOi of the first magnet arrangement 110, is the same as a radial width of the second magnet arrangement 120, i.e. a difference between the outer diameter 120o and an inner diameter 120i of the second magnet arrangement 110. This is but one example, and the radial widths of the magnet arrangements 110, 120 may very well be different. In some examples, the radial width of an inner magnet arrangement, in Fig. 3 A the second magnet arrangement 120, is advantageously greater than the radial width of an outer magnet arrangement, in Fig. 3 A the first magnet arrangement 110, in order to provide equal magnetic field strengths from both magnet arrangements 110, 120.

[0054] As the first magnet arrangement 110 and the second magnet arrangement 120 are concentric with the first axis X, the top view Fig. 3 A indicate that the second magnet arrangement 120 is inside the first magnet arrangement 110. It should be mentioned that the magnet arrangements 110, 120 may be axially distanced such there is no radial overlap between the first magnet arrangement 110 and the second magnet arrangement 120. Regardless of a mutual arrangement of the first magnet arrangement 110 and the second magnet arrangement 120 along the first axis X, the first magnet arrangement 110 and the second magnet arrangement 120 are arranged such that an annular space 130 extending at least partly through the magnetic circuit 100 along the first axis X is formed.

[0055] In all Figs. 3A-C, the voice coils 141, 142 are arranged inside the annular space 130. In Fig. 3A, the voice coils 141, 142 are formed with similar diameters as in the arrangement mentioned (but not shown) in reference to Fig. 2 above. In an advantageous arrangement, a diameter 14 li of the first voice coil 141 is different from a diameter 142o of the second voice coil 142. In Fig. 3B, an inner diameter 14 li of the first voice coil 141 is greater than an outer diameter 142o of the second voice coil 142. This allows the excursion capability (axial movement) of the voice coils 141, 142 to increase as the voice coils 141, 142 are free to move the full axial extension of their respective partial magnetic circuit 100a, 100b without physically interfering with each other, i.e. colliding.

[0056] In Fig. 3C, a cross-sectional side view of the magnetic circuit in Fig. 3A is shown. In Fig. 3C, the substantially cylindrical magnet arrangements 110, 120 are axially magnetized with their respective directions 110’, 120’ being axially opposite. The magnetic circuit 100 is formed from the first partial magnetic circuit 100a and the second partial magnetic circuit 100b. The first partial magnetic circuit 100a extends from the north pole 111 of the first magnet arrangement 110 to the south pole 122 of the second magnet arrangement 120. The first voice coil 141 is arranged in the first partial magnetic circuit 110a and movable along the first axis X. The second partial magnetic circuit 100b extend from the north pole 121 of the second magnet arrangement 120 to the south pole 112 of the first magnet arrangement 110. The second voice coil 142 is arranged in the second partial magnetic circuit 110b and movable along the first axis X. The partial magnetic circuits 100a, 100b extend at least partly through the annular space 130 and the voice coils 141, 142 are axially movable within the annular space 130.

[0057] A distance between the north pole 111 of the first magnet arrangement 110 and the south pole 122 of the second magnet arrangement 120 and a distance between the north pole 121 of the second magnet arrangement 120 and a south pole 112 of the first magnet arrangement 110 will affect the reluctance of the partial magnetic circuits 100a, 100b. An increased distance will increase the reluctance and in order to e.g. reduce a required current of a voice coil 141, 142 to move a specific axial distance, the reluctance of the partial magnetic circuits 100a, 100b and the magnetic circuit 100 is advantageously reduced.

[0058] In order to decrease reluctance of the magnetic circuit 100 and to direct the magnetic fields of the partial magnetic circuits 100a, 100b, the magnetic circuit 100 shown in Fig. 4, comprises magnetic pole members 114, 115, 124, 125. A magnetic pole member 114, 115, 124, 125 is a magnetic member provided at a pole 111, 112, 121, 122 of a magnet arrangement 110, 120. Specifically with an axially magnetized magnet arrangement 110, 120, the pole member 114, 115, 124, 125 will provide a radial guide for the magnetic field, effectively concentrating the magnetic field and increasing the magnetic flux of the associated partial magnetic circuit 100a, 100b. In Fig. 4, a first magnetic pole member 114 is connected to the south pole 112 of the first magnet arrangement 110. A first magnetic pole member 124 is connected to the south pole 122 of the second magnet arrangement 120. A second magnetic pole member 115 is connected to the north pole 111 of the first magnet arrangement 110. A second magnetic pole member 125 is connected at the north pole 121 of the second magnet arrangement 120. In Fig. 4, the first partial magnetic circuit 100a extends from the north pole 111 of the first magnet arrangement 110, via the second magnetic pole member 115 of the first magnet arrangement 110, through the annular space 130 to the first magnetic pole member 124 of the second magnet arrangement 120 and onwards to the south pole 122 of the second magnet arrangement 120. Similarly, the second partial magnetic circuit 100b extends from the north pole 121 of the second magnet arrangement 120, via the second magnetic pole member 125 of the second magnet arrangement 120, through the annular space 130 to the first magnetic pole member 114 of the first magnet arrangement 110 and onwards to the south pole 112 of the first magnet arrangement 110.

[0059] In Fig. 4, a distance between opposing radial surfaces of respective pole members 114, 115, 124, 125 of each partial magnetic circuit 100a, 100b is reduced compared to a distance between axial surfaces of the respective magnet arrangements 110, 120 of each partial magnetic circuit 100a, 100b. This reduces the reluctance of the partial magnetic circuits 100a, 100b and stray magnetic fields are reduced.

[0060] In Fig. 4, the highest magnetic flux of each partial magnetic circuit 100a, 100b will be in the radial portion of the annular space 130 between the respective pole members 114, 115, 124, 125 of each partial magnetic circuit 100a, 100b. This portion of the annular space 130 and the partial magnetic circuit 100a, 100b may be referred to as a magnet gap. To this end, the voice coils 141, 142 are advantageously arranged radially between the respective pole members 114, 115, 124, 125 of each partial magnetic circuit 100a, 100b. Advantageously, an axial extension of the voice coils 141, 142 is sufficiently greater than an axial extension of the associated pole members 114, 115, 124, 125 such that a portion of the voice coil 141, 142 will always be provided between the respective pole members 114, 115, 124, 125 for their full axial movement, excursion. This arrangement is commonly referred to as an overhung arrangement as the voice coils 141, 142 extend outside the associated magnet gap.

[0061] In order to further reduce the reluctance and increase the magnetic flux of the magnet gap, the pole members 114, 115, 124, 125 may be configured to extend radially into the annular space 130. This is shown in Fig. 5 wherein the second pole member 115 connected to the north pole 111 of the first magnet arrangement 110 is configured to extend radially into the annular space 130 towards the south pole 122 of the second magnet arrangement 120. Similarly, the second pole member 125 connected to the north pole 121 of the second magnet arrangement 110 is configured to extend radially into the annular space 130 towards the south pole 112 of the first magnet arrangement 110. This effectively reduces a radial distance of the magnet gap, decreasing the reluctance of the magnetic circuit 100 and increasing the magnetic flux of the magnet gaps.

[0062] In Fig. 4 and Fig. 5, all poles 111, 112, 121, 122 are provided with pole members 114, 115, 124, 125. This is to exemplify the concept and examples where only one, two or three poles 111, 112, 121, 122 are provide with pole members 114, 115, 124, 125 are well within the scope of the present disclosure. Analogously, in Fig. 5, the second pole members 115, 125 extend into the annular space 130. This is but one example and examples where only one, three, or all four pole members 111, 112, 121, 122 extend into the annular space 130 are well within the scope of the present disclosure.

[0063] In Fig. 6, a partial view of a magnetic circuit 100 according to one example is shown. The magnetic circuit 100 in Fig. 6 is assumed to be symmetrical around the first axis X. In Fig. 6, the first magnet arrangement 110 and the second magnet arrangement 120 are axially magnetized magnet arrangements. A magnetic pole member 114, 115, 124, 125 is connected to each of the poles 111, 112, 121, 122 of the magnet arrangements 110, 120. In Fig. 6, the second pole members 115, 125 connected to the north poles 111, 121 of the magnet arrangements 110, 120 are configured to extend radially into the annular space 130. The first pole members 114, 124 connected to the south poles 112, 122 of the magnet arrangements 110, 120 are configured with axial extension larger than an axial extension of the second pole members 115, 125. As a result, the magnetic field of the first partial magnetic circuit 100a will provide a comparably high magnetic flux at the radial surface of the second pole member 115 connected to the north pole 111 of the first magnet arrangement 110 that faces the annular space 130. The magnetic field of the first partial magnetic circuit 100a will spread towards a radial surface of the first pole member 124 connected to the south pole 122 of the second magnet arrangement 120 that faces the annular space. The corresponding is true for the second partial magnetic circuit 100b. These comparably axially spread magnet fields provides an axially extended magnet gap. This allows for the voice coils 141, 142 to be configured with a reduced axial extension such that the entire voice coil 141, 142 is always within the magnet gap.

[0064] In Fig. 6, an optional cylinder 150 is arranged concentrically with the first axis X. The cylinder 150 is arranged in the annular space 130 and divide the annular space 130 in a first annular subspace 131 and a second annular subspace 132. The first annular subspace 131 is formed between the first magnet arrangement 110 and the cylinder 150 and a second annular subspace 132 is formed between the cylinder 150 and the second magnet arrangement 120. The first voice coil 141 is arranged inside the first annular subspace 131 and the second voice coil 142 is arranged inside the second annular subspace 132. The cylinder 150 may be a cylindrical pipe, a cylindrical member or any suitable arrangement being cylindrical around the first axis X. The cylinder 150 is advantageously a structural piece providing mechanical support for the magnetic circuit 100. The cylinder 150 is advantageously at least mechanically connected to the second pole members 115, 125 to mechanically stabilize the magnetic circuit 100.

[0065] In some examples, the cylinder 150 is a magnetic cylinder 150. In such examples, the cylinder 150 will act as second pole members 115, 125 of both the first and second magnet arrangements 110, 120. For an underhung design the centre piece may be made ferritic and therefore form a part of the magnetic circuit. Assuming that the cylinder 150 of Fig. 6 is a magnetic cylinder, the magnetic field of the second partial magnetic circuit 110b would be axially spread along the cylinder 150. That is to say, the second partial magnetic circuit 110b is provided from the north pole 121 of the second magnet arrangement 120, to the magnetic cylinder 150, to the first pole member 114 of the first magnet arrangement 110 and to the south pole 112 of the first magnet arrangement 110. Correspondingly, the first partial magnetic circuit 110a is provided from the north pole 111 of the first magnet arrangement 110, to the magnetic cylinder 150, to the first pole member 124 of the second magnet arrangement 120 and to the south pole 122 of the second magnet arrangement 120.

[0066] In some examples the cylinder 150 may be an electrically conducting cylinder 150. In such examples, the cylinder 150 may be considered a shorting ring. This will improve the inductance of the magnetic circuit 100.

[0067] The arrangement of the voice coils 141, 142 shown in Fig. 6 may be referred to as an underhung arrangement. However, if the first pole members 114, 124 would have been axially thin in relation to an axial extension of the voice coils 141, 142, such arrangement may be referred to as on overhung arrangement. In the underhung arrangement shown in Fig. 6, the cylinder 150 is advantageously a magnetic cylinder 150.

[0068] In Fig. 6, the second pole members 115, 125 extends into the annular space 130 and an axial extension of the first pole member 114, 124 exceeds an axial extension of the second pole members 115, 125. This is just one example, in other examples, pole members 114, 115, 124, 125 extending into the annular space 130 are configured with an axial extension similar to, or greater than, the axial extension of the other pole members 114, 115, 124, 125. However, the shown arrangement is advantageous as the axial movement of the voice coils 141, 142 as a function of an axial extension of the magnetic circuit 100 is greater. In other words, the magnetic circuit 100, and an associated speaker, may be more compact. Further to this, the pole members 114, 115, 124, 125 extending into the annular space are not required to be connected to the north poles 111, 121 of the magnet arrangements 110, 120, but may very well be connected to the south poles 112, 122 of the magnet arrangements 110, 120. As previously mentioned, both magnet arrangements 110, 120 or both poles 111, 112, 121, 122 of the magnet arrangements 110, 120 are not required to be provided with pole members 114, 115, 124, 125.

[0069] It is not a requirement that both magnet arrangements 110, 120 are magnetized along the same axis, i.e. axially or radially. In Fig. 7, a cross-sectional partial view of an exemplary magnetic circuit 100 is shown. The magnetic circuit 100 in Fig. 7 is assumed to be symmetrical around the first axis X. In Fig. 7, the first magnet arrangement 110 is axially magnetized and the second magnet arrangement 120 is radially magnetized. A first pole member 114 is connected to the south pole 112 of the first magnet arrangement 110 and a second pole member 115 is connected to the north pole 111 of the first magnet arrangement. The second pole member 115 of the first magnet arrangement 110 extends radially into the annular space 130. A first pole member 124 is connected to the south pole 122 of the radially magnetized second magnet arrangement 120. The first pole member 114 of the second magnet arrangement 120 is arranged to extend along the first axis X and along the annular space 130. A cylinder 150 is connected to the north pole 121 of the second magnet arrangement 120 and arranged in the annular space 130 dividing the annular space 130 in a first annular subspace 131 and a second annular subspace 132 as described in reference to Fig. 6. In Fig. 7, the first partial magnetic circuit 100a is provided from the north pole 111 of the first magnet arrangement 110, via the second pole member 115 of the first magnet arrangement, through the annular space 130, to the first pole member 124 of the second magnet arrangement and to the south pole 122 of the second magnet arrangement 120. The second partial magnetic circuit 110b is provided from the north pole 121 of the second magnet arrangement 120, through the cylinder 150 providing mechanical support for the magnetic circuit 100 to the first pole member 114 of the first magnet arrangement 110 and to the south pole 112 of the first magnet arrangement 110. The first voice coil 141 is arranged in the first partial magnetic circuit 100a in the second subspace 132 of the annular space 130. The second voice coil 142 is arranged in the second partial magnetic circuit 100b in the first subspace 131 of the annular space 130.

[0070] In Fig. 8, a cross-sectional partial view of an exemplary magnetic circuit 100 is shown. The magnetic circuit 100 in Fig. 8 is assumed to be symmetrical around the first axis X. The magnetic circuit of Fig. 8 corresponds to the magnetic circuit 100 of Fig. 7 but with the difference that the first magnet arrangement 110 is radially magnetized and the second magnet arrangement 120 is axially magnetized.

[0071] In Fig. 9, a cross-sectional partial view of an exemplary magnetic circuit 100 is shown. The magnetic circuit 100 in Fig. 9 is assumed to be symmetrical around the first axis X. As in Fig. 2, both the first magnet arrangement 110 and the second magnet arrangement 120 are radially magnetized. A first pole member 114 is connected to the south pole 112 of the first magnet arrangement 110 and arranged to extend along the first axis X. A corresponding first pole member 124 is connected to the south pole 122 of the second magnet arrangement 120. A cylinder 150 is connected between the north poles 111, 121 of the magnet arrangements 110, 120 to provide mechanical support for the magnetic circuit 100. In Fig. 9, the first partial magnetic circuit 100a is provided from the north pole 111 of the first magnet arrangement 110 through the second subspace 132 of the annular space 130, to the first pole member 124 of the second magnet arrangement 120 and to the south pole 122 of the second magnet arrangement 120. The second partial magnetic circuit 110b is provided from the north pole 121 of the second magnet arrangement 120 through the first sub space 131 of the annular space 130 to the first pole member 114 of the first magnet arrangement 110 and to the south pole 112 of the first magnet arrangement 110. The first voice coil 141 is arranged in the first partial magnetic circuit 100a in the second subspace 132 of the annular space 130. The second voice coil 142 is arranged in the second partial magnetic circuit 100b in the first subspace 131 of the annular space 130.

[0072] As exemplified above, the magnetic circuit 100 of the present disclosure may be formed in numerous different ways. Mutual dimensions and arrangement of the magnet arrangements 110, 120 or the voice coils 141, 142 may be chosen freely as long as the magnet arrangements 110, 120 and the voice coils 141, 142 are all concentric with the first axis X. Further, the north poles 111, 121 of the magnet arrangements 110, 120 face different directions 110’, 120’. However, as seen in e.g. Fig. 8, the directions 110’, 120’ are not necessarily opposite.

[0073] In Fig. 10, a cross-sectional view of an exemplary dual membrane driver 200 is shown. The dual membrane driver 200 comprises the magnetic circuit 100 described with reference to Fig. 5. The dual membrane driver 200 comprises a first membrane 220a and a second membrane 220b, both being concentric with the first axis X and arranged at opposite axial ends of the magnetic circuit 100. The membranes 220a, 220b face in opposite directions. The first membrane 220a is connected to the first voice coil 141 and the second membrane 220b is connected to the second voice coil 142. When currents are passed through the voice coils 141, 142, the magnetic field induced in the voice coils 141, 142 will cause the voice coils 141, 142 to move axially in the constant magnetic field provided by the magnetic circuit 100. As the voice coils 141, 142 move, the membranes 220a, 220b will be moved shifting air and causing sound corresponding to the currents passed through the voice coils 141, 142.

[0074] As mentioned, the magnetic circuit 100 of the present disclosure allows for the use of standard components when designing the dual membrane driver 200. To this end, the dual membrane driver 200 may comprise standard baskets 210a, 210b, standard surrounds 230a, 230b, standard voice coils 141, 142 and standard spiders 240a, 240b.

[0075] In Fig. 11, a cross-sectional view of a preferred example of an exemplary dual membrane driver 200 is shown. The dual membrane driver 200 of Fig. 11 is identical to the dual membrane driver 200 of Fig. 10 but with the difference that it comprises the magnetic circuit 100 described in reference to Fig. 2.

[0076] The skilled person will understand that a dual membrane driver 200 according to the present disclosure may comprise any magnetic circuit 100, or any feature of magnetic circuits 100, presented herein.

[0077] In Fig. 12A, a front planar view of a speaker 300 is shown. In Fig. 12B, a corresponding back planar view of the speaker 300 is shown. The speaker 300 comprises a dual membrane driver 200 as presented herein. The speaker 300 comprises a housing 310 with opening for the membranes 220a, 220b of the dual membrane driver 200.

[0078] The skilled person will appreciate that the present disclosure is focused on magnetic circuits 100 for use in dual membrane drivers 200. For this reason, structural members have been omitted from the disclosure for reasons of brevity. The skilled person is, after digesting the teachings of the present disclosure, fully capable of forming a magnetic circuit 100, a dual membrane driver 200 and a speaker 300 as presented herein.

[0079] It should be mentioned that a prior art magnetic circuit for a single membrane driver generally comprise an axially oriented magnet that creates a radial magnet field for the voice coil. Historically, a dual membrane driver is generally provided by stacking two such magnetic circuits back to back along a common axis. This adds weight, cost, and increase use of rare earth magnets.

[0080] As mentioned, the magnetic circuit 100 of the present disclosure utilize at least two magnet arrangement 110, 120, with different orientation from a magnetization perspective. This is provided in order to steer the magnetic fields more efficiently to the desired locations (the two magnet gaps). By doing this, a very compact and lightweight dual membrane driver is obtained. This dual membrane driver offers a strong force factor for two similar opposed membranes. It is in essence nesting two driver motors in the same space, which at the same time increases an efficiency of both membrane drivers. As the magnet gaps are concentric it is possible to use standard suspension solutions and voice coils which leads to fast prototyping and reduced cost for new driver designs. The front of each magnet is used to provide flux in one of the magnet gaps, while the rear is used to steer the magnet field from other magnet in the correct direction, increasing the flux in that magnets gap. All the magnetic circuits of the present disclosure reduce stray magnetic fields and increase the flux in the magnet gap. This is provided by the symbiotic relationship between the two magnet arrangements 110, 120. It should be mentioned that further magnet arrangements may be added to tighter control the magnetic field.

[0081] Modifications and other variants of the described embodiments will come to mind to one skilled in the art having benefit of the teachings presented in the foregoing description and associated drawings. Therefore, it is to be understood that the embodiments are not limited to the specific example embodiments described in this disclosure and that modifications and other variants are intended to be included within the scope of this disclosure. Furthermore, although specific terms may be employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. Therefore, a person skilled in the art would recognize numerous variations to the described embodiments that would still fall within the scope of the appended claims. Furthermore, although individual features may be included in different claims (or embodiments), these may possibly advantageously be combined, and the inclusion of different claims (or embodiments) does not imply that a combination of features is not feasible and / or advantageous. In addition, singular references do not exclude a plurality. Finally, reference signs in the claims are provided merely as a clarifying example and should not be construed as limiting the scope of the claims in any way.

Claims

CLAIMS1. A magnetic circuit (100) configured for use in a dual membrane driver (200), the magnetic circuit (100) comprising: a first substantially cylindrically formed magnet arrangement (110) having a north pole (111) facing in a first direction (110’), the first magnet arrangement (110) being concentric with a first axis (X), a second substantially cylindrically formed magnet arrangement (120) having a north pole (121) facing in a second direction (120’) being different from the first direction (110’), the second magnet arrangement (120) being concentric with the first axis (X) and arranged radially and / or axially distanced from the first magnet arrangement (110) such that a first partial magnetic circuit (100a) is formed from the north pole (111) of the first magnet arrangement (110) to a south pole (122) of the second magnet arrangement (120) and a second partial magnetic circuit (100b) is formed from the north pole (121) of the second magnet arrangement (120) to a south pole (112) of the first magnet arrangement (110), a first voice coil (141) concentric with the first axis (X) within the first partial magnetic circuit (100a), and a second voice coil (142) concentric with the first axis (X) within the second partial magnetic circuit (100b).

2. The magnetic circuit (100) of claim 1, wherein an outer diameter (142o) of the second voice coil (142) is smaller than an inner diameter ( 141 i) of the first voice coil (141).

3. The magnetic circuit (100) of claim 1 or 2, wherein an outer diameter (120o) of the second magnet arrangement (120) is smaller than an inner diameter (1 lOi) of the first magnet arrangement (110) such that an annular space (130) extending at least partly through the magnetic circuit (100) along the first axis (X) is formed,wherein the first partial magnetic circuit (100a) and the second partial magnetic circuit (100b) are at least partly within the annular space (130).

4. The magnetic circuit (100) of claim 3, wherein at least one of the first magnet arrangement (110) or the second magnet arrangement (120) is an axially magnetized magnet, wherein a magnetic pole member (114, 115, 124, 125) is connected to the north pole (111, 121) or the south pole (121, 122) of the at least one axially magnetized magnet.

5. The magnetic circuit (100) of claim 4, wherein the magnetic pole member (114, 115, 124, 125) is arranged to extend into the annular space (130).

6. The magnetic circuit (100) of claim 4 or 5 wherein both the first magnet arrangement (110) and the second magnet arrangement (120) are axially magnetized magnets, wherein a first magnetic pole member (114, 115) is connected to the north pole (111) or the south pole (112) of the first magnet arrangement (110), and wherein a second magnetic pole member (124, 125) is connected to the corresponding one of the north pole (121) or the south pole (122) of the second magnet arrangement (120).

7. The magnetic circuit (100) of any one of claims 4 to 6, wherein the second magnet arrangement (120) is arranged at least partly inside the first magnet arrangement (110) along the first axis (X), and wherein the first voice coil (141) is arranged radially outside of the second magnetic pole member (124, 125), and wherein the second voice coil (142) is arranged radially inside of the first magnetic pole member (114, 115).

8. The magnetic circuit (100) of any one of claims 4 to 6, further comprising a cylinder (150) concentrically with the first axis (X) and being arranged to connect the first magnetic pole member (114, 115) to the second magnetic pole member (124, 125) dividing the annular space (130) in a first annular subspace(131) between the first magnet arrangement (110) and the cylinder (150) and a second annular subspace (132) between the cylinder (150) and the second magnet arrangement (120), and wherein the first voice coil (141) is arranged inside the first annular subspace (131) and the second voice coil (142) is arranged inside the second annular subspace (132).

9. The magnetic circuit (100) of any one of claims 3 to 5, wherein one of the first magnet arrangement (110) or the second magnet arrangement (120) is a radially magnetized magnet, and wherein a cylinder (150) is connected to the north pole (111, 121) or the south pole (112, 122) of the radially magnetized magnet and arranged concentrically with first axis (X) inside the annular space (130) dividing the annular space (130) in a first annular subspace (131) between the first magnet arrangement (110) and the cylinder (150) and a second annular subspace (132) between the cylinder (150) and the second magnet arrangement (120), and wherein the first voice coil (141) is arranged inside the first annular subspace (131) and the second voice coil (142) is arranged inside the second annular subspace (132).

10. The magnetic circuit (100) of claim 9, wherein both the first magnet arrangement (110) and the second magnet arrangement (120) are radially magnetized magnets.

11. The magnetic circuit (100) of claims 5 and 9, wherein the cylinder (150) is connected to the magnetic pole member (114, 115, 124, 125).

12. The magnetic circuit (100) of any one of claims 8 to 11, wherein the cylinder (150) is a magnetic cylinder (150).

13. The magnetic circuit (100) of any one of claims 8 to 12, wherein the cylinder (150) is an electrically conducting cylinder (150).

14. The magnetic circuit (100) of claim 1 or 2, wherein an outer diameter (120o) of the second magnet arrangement (120) is substantially equal to an outer diameter (1 lOo) of the first magnet arrangement (110) and / or an inner diameter (120i) of the second magnet arrangement (120) is substantially equal to an inner diameter (1 lOi) of the first magnet arrangement (110), wherein both the first magnet arrangement (110) and the second magnet arrangement (120) are radially magnetized magnets.

15. A dual membrane driver (200) comprising the magnetic circuit (100) of any one of claims 1 to 14, a first membrane (220a) being concentric with the first axis(X) of the magnetic circuit (100), a second membrane (220b) being concentric with the first axis (X) of the magnetic circuit (100) and facing in an opposite direction of the first membrane (220a), wherein the first membrane (220a) is connected to the first voice coil (141) and the second membrane (220b) is connected to the second voice coil (142).

16. A speaker (300) comprising a dual membrane driver (200) of claim 15.

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